Riddles of Philosophy
Part II
GA 18
II. Darwinism and World Conception
[ 1 ] If the thought of the teleological structure of nature was to be reformed in the sense of a naturalistic world conception, the purpose-adjusted formation of the organic world had to be explained in the same fashion as the physicist or the chemist explains the lifeless processes. When a magnet attracts iron shavings, no physicist will assume that there is a force at work in the magnet that aims toward the purpose of the attraction. When hydrogen and oxygen form water as a compound, the chemist does not interpret this process as if something in both substances had been actively striving toward the purpose of forming water. An explanation of living beings that is guided by a similar naturalistic mode of thinking must conclude that organisms become purpose-adjusted without anything in nature planning this purpose-conformity. This conformity comes to pass without being anywhere intended. Such an explanation was given by Charles Darwin. He took the point of view that there is nothing in nature that plans the design. Nature is never in a position to consider whether its products are adequate to a purpose or not. It produces without choosing between what is adequate to a purpose and what is not.
[ 2 ] What is the meaning of this distinction anyhow? When is a thing in conformity with a purpose? Is it not when it is so arranged that the external circumstances correspond to its needs, to its life conditions? A thing is inadequate to purpose when this is not the case. What will happen if, while a complete absence of plan in nature characterizes the situation, formations of all degrees of purpose-conformity, from the most to the least adequately adapted form, come into existence? Every being will attempt to adapt its existence to the given circumstances. A being well-adjusted to life will do so without much difficulty; one less adequately endowed will succeed only to a lesser degree. The fact must be added to this that nature is not a parsimonious housekeeper in regard to the production of living beings. The number of germs is prodigious. The abundant production of germs is backed up by inadequate means for the support of life. The effect of this will be that those beings that are better adapted to the acquisition of food will more easily succeed in their development. A well-adapted organic being will prevail in the strife for existence over a less adequately adjusted one. The latter must perish in this competition. The fit, that is to say, the one adapted to the purpose of life, survives; the unfit, that is, the one not so adapted, does not. This is the “struggle for life.” Thus, the forms adequate to the purpose of life are preserved even if nature itself produces, without choice, the inadequate side by side with the adequate. Through a law, then, that is as objective and as devoid of any wise purpose as any mathematical or mechanical law of nature can be, the course of nature's evolution receives a tendency toward a purpose-conformity that is not originally inherent in it.
[ 3 ] Darwin was led to this thought through the work of the social economist Malthus entitled Essay on the Principle of Population (1798). In this essay the view is advanced that there is a perpetual competition going on in human society because the population grows at a much faster pace than the supply of food. This law that Malthus had stated as valid for the history of mankind, was generalized by Darwin into a comprehensive law of the whole world of life.
[ 4 ] Darwin now set out to show how this struggle for existence becomes the creator of the various forms of living beings and that thereby the old principle of Linnaeus was overthrown, that “we have to count as many species in the animals and vegetable kingdoms as had been principally created.” The doubt against this principle was clearly formed in Darwin's mind when, in the years 1831–36, he was on a journey to South America and Australia. He tells how this doubt took shape in him.
When I visited the Galapagos Archipelago during my journey on H.M.S. Beagle, at a distance of about 500 miles from the shores of South America, I saw myself surrounded by strange species of birds, reptiles and snakes, which exist nowhere else in the world. Almost all of them bore the unmistakable stamp of the American continent. In the song of the mocking-thrush, in the sharp scream of the vultures, in the large candlestick-like opuntias I noticed distinctly the vicinity of America; and yet these islands were separated from the continent by many miles and were very different in their geological constitution and their climate. Even more surprising was the fact that most of the inhabitants of each of the individual islands of the small archipelago were specifically different although closely related. I often asked myself how these strange animals and men had come into being. The simplest way seemed to be that the inhabitants of the various islands were descended from one another and had undergone modifications in the course of their descent, and that all inhabitants of the archipelago were descendants of those of the nearest continent, namely, America, where the colonization naturally would have its origin. But it was for a long time an unexplainable problem to me how the necessary modification could have been obtained.
The answer to this question is contained in the naturalistic conception of the evolution of the living organism. As the physicist subjects a substance to different conditions in order to study its properties, so Darwin, after his return, observed the phenomena that resulted in living beings under different circumstances. He made experiments in breeding pigeons, chickens, dogs, rabbits and plants. Through these experiments it was shown that the living forms continuously change in the course of their propagation. Under certain circumstances some living organisms change so much after a few generations that in comparing the newly bred forms with their ancestors, one could speak of two completely different species, each of which follows its own design of organization. Such a variability of forms is used by the breeder in order to develop organisms through cultivation that answer certain demands. A breeder can produce a species of sheep with an especially fine wool if he allows only those specimens of his flock to be propagated that have the finest wool. The quality of the wool is then improved in the course of the generations. After some time, a species of sheep is obtained which, in the formation of its wool, has progressed far beyond its ancestors. The same is true with other qualities of living organisms. Two conclusions can be drawn from this fact. The first is that nature has the tendency to change living beings; the second, that a quality that has begun to change in a certain direction increases in that direction, if in the process of propagation of organic beings those specimens that do not have this quality are excluded. The organic forms then assume other qualities in the course of time, and continue in the direction of their change once this process has begun. They change and transmit the changed qualities to their descendants.
[ 5 ] The natural conclusion from this observation is that change and hereditary transmission are two driving principles in the evolution of organic beings. If it is to be assumed that in the natural course of events in the world, formations that are adapted to life come into being side by side with those not adapted as well as others, it must also be supposed that the struggle for life takes place in the most diversified forms. This struggle effects, without a plan, what the breeder does with the aid of a preconceived plan. As the breeder excludes the specimen from the process of propagation that would introduce undesired qualities into the development, so the struggle for life eliminates the unfit. Only the fit survive in evolution. The tendency for perpetual perfection enters thus into the evolutionary process like a mechanical law. After Darwin had seen this and after he had thereby laid a firm foundation to a naturalistic world conception, he could write the enthusiastic words at the end of his work, The Origin of Species, which introduced a new epoch of thought:
Thus, from the war of nature, from famine and death the most exalted object which we are capable of conceiving, namely, the production of the higher animals, directly follows. There is grandeur in this view of life, with its several powers having been originally breathed by the Creator into a few forms or into one; and that, whilst this planet has gone cycling on according to the fixed law of gravity, from so simple a beginning endless forms most beautiful and most wonderful have been and are being evolved.
At the same time one can see from this sentence that Darwin does not derive his conception from any anti-religious sentiment but merely from the conclusions that for him follow from distinctly significant facts. It was not hostility against the needs of religious experience that persuaded him to a rational view of nature, for he tells us distinctly in his book how this newly acquired world of ideas appeals to his heart.
Authors of the highest eminence seem to be fully satisfied with the view that each species has been independently created. To my mind it accords better with what we know of the laws impressed in matter by the Creator that the production and extinction of the past and present inhabitants of the world should have been due to secondary causes, like those determining the birth and death of the individual. When I view all beings not as special creations, but as the linear descendants of some few beings which lived long before the first bed of the Cambrian system was deposited, they seem to me to become ennobled. . . . Hence, we may look with some confidence to a secure future of great length. And as natural selection works solely by and for the good of each being, all corporeal and mental endowments will tend to progress toward perfection.
[ 6 ] Darwin showed in great detail how the organisms grow and spread, how, in the course of their development, they transmit their properties once they are acquired, how new organs are produced and change through use or through lack of use, how in this way the organic beings are adjusted to their conditions of existence and how finally through the struggle for life a natural selection takes place by means of which an ever increasing variety of more and more perfect forms come into being.
[ 7 ] In this way an explanation of teleologically adjusted beings seems to be found that requires no other method for organic nature than that which is used in inorganic nature. As long as it was impossible to offer an explanation of this kind it had to be admitted, if one wanted to be consistent, that everywhere in nature where a purpose-adjusted being came into existence, the intervention of an extraneous power had to be assumed. In every such case one had to admit a miracle.
[ 8 ] Those who for decades before the appearance of Darwin's work had endeavored to find a naturalistic world and life conception now felt most vividly that a new direction of thought had been given. This feeling is expressed by David Friedrich Strauss in his book, The Old and the New Faith (1872).
One sees this is the way it must go; this is where the new banner is waving sprightly in the wind. It is a real joy in the sense of the loftiest joys of intellectual advance. We philosophers and critical theologians talked and talked to discredit the idea of a miracle. Our decree had no effect whatever, because we did not know how to demonstrate this idea as a superfluous one, because we did not know how to avoid it for we did not know of any energy of nature with which we could replace it where it seemed to be most necessary to be assumed. Darwin has demonstrated this energy of nature, this procedure of nature; he has opened the door through which a fortunate posterity will throw out the miracle once and for all times. Everyone who knows how much depends on miracles will praise him for that deed as one of the greatest benefactors of the human race.
[ 9 ] Through Darwin's idea of fitness it is possible to think the concept of evolution really in the form of a natural law. The old doctrine of involution, which assumes that everything that comes into existence has been there in a hidden form before (compare pages in Part 1 Chapter IX), had been deprived of its last hope with this step. In the process of evolution as conceived by Darwin, the more perfect form is in no way contained in the less perfect one, for the perfection of a higher being comes into existence through processes that have nothing whatsoever to do with the ancestors of this being. Let us assume that a certain evolutionary series has arrived at the marsupials. The form of the marsupials contains nothing at all of a higher, more perfect form. It contains only the ability to change at random in the course of its propagation. Certain circumstances then come to pass that are independent of any “inner” latent tendency of development of the form of the marsupials but that are such that of all possible variations (mutations) the pro-simians survive. The forms of the marsupials contained that of the pro-simians no more than the direction of a rolling billiard ball contains the path it will take after it has been deflected from its original course by a second billiard ball.
[ 10 ] Those accustomed to an idealistic mode of thinking had no easy time in comprehending this reformed conception of evolution. Friedrich Theodor Vischer, a man of extraordinary acumen and subtlety of spirit who had come from Hegel's school, writes as late as 1874 in an essay:
Evolution is an unfolding from a germ that proceeds from attempt to attempt until the picture that the germ contained latently as a possibility has become real. But once this is accomplished it stops and holds on to the form that is found, keeping it as a permanent one. Every concept as such would lose its firm outline if we were to consider the types that have existed on our planet for so many thousands of years as forever variable and above all if we were so to consider our own human type. We should then be unable any longer to trust our thoughts, the laws conceived by our thinking, our feelings, the pictures of our imagination, all of which are nothing but the clarifying imitations of forms of nature as it is known to us. Everything becomes questionable.
[ 11 ] In another passage in the same essay he says:
I still find it a little hard, for instance, to believe that we should owe our eye to the process of seeing, our ear to that of hearing. The extraordinary weight that is given to the process of natural selection is something I am not quite satisfied with.
[ 12 ] If Vischer had been asked whether or not he imagined that hydrogen and oxygen contained within themselves in a latent form a picture of water to make it possible for the latter to develop from the former, he would undoubtedly have answered, “No, neither in oxygen nor in hydrogen is there anything contained of the water that is formed; the conditions for the formation of this substance are given only when hydrogen and oxygen are combined under certain circumstances.” Is the situation then necessarily different when, through the two factors of the marsupials and the external conditions, the pro-simians came into being? Why should the pro-simians be contained as a possibility, as a scheme, in the marsupials in order to be capable of being developed from them? What comes into being through evolution is generated as a new formation without having been in existence in any previous form.
[ 13 ] Thoughtful naturalists felt the weight of the new teleological doctrine no less than Strauss. Hermann Helmholtz belongs, without doubt, among those who, in the eighteen-fifties and sixties, could be considered as representatives of such thoughtful naturalists. He stresses the fact that the wonderful purpose-conformity in the structure of living organisms, which becomes increasingly apparent as science progresses, challenges the comparison of all life processes to human actions. For human actions are the only series of phenomena that have a character that is similar to the organic ones. The fitness of the arrangements in the world of organisms does, according to our judgment, in most cases indeed far surpass what human intelligence is capable of creating. It therefore cannot surprise us that it has occurred to people to seek the origin of the structure and function of the world of living beings in an intelligence far superior to that of man. Helmholtz says:
Before Darwin one could admit two kinds of explanations for the fact of organic purpose adjustment, both of which depended on an interference of a free intelligence in the course of natural phenomena. One either considered, according to the vitalistic theory, the life-processes as perpetually guided by a life-soul; or one saw in each species an act of a supernatural intelligence through which it was supposed to have been generated. . . . Darwin's theory contains an essentially new creative thought. It shows that a purpose-adjustment of the form in the organisms can come to pass also without interference of an intelligence through the random effect of a natural law. This is the law of the transmission of individual peculiarities from the parents to the descendants, a law that was long known and recognized but was merely in need of a definite demarcation.
[ 14 ] Helmholtz now is of the opinion that such a demarcation is given by the principle of natural selection in the struggle for existence. A scientist who, like Helmholtz, belongs to the most cautious naturalists of that time, J. Henle, said in a lecture, “If the experiences of artificial breeding were to be applied to the hypothesis of Oken and Lamarck, it would have to be shown how nature proceeds in order to supply the mechanism through which the experimental breeder obtains his result. This is the task Darwin set for himself and that he pursued with admirable industry and acumen.”
[ 15 ] The materialists were the ones who felt the greatest enthusiasm of all from Darwin's accomplishment. They had long been convinced that sooner or later a man like him would have to come along who would throw a philosophical light on the vast field of accumulated facts that was so much in need of a leading thought. In their opinion, the world conception for which they had fought could not fail after Darwin's discovery. Darwin approached his task as a naturalist. At first he moved within the limits reserved to the natural scientist. That his thoughts were capable of throwing a light on the fundamental problems of world conception, on the question of man's relation to nature, was merely touched upon in his book:
[ 16 ] In the future I see open fields for far more important researches. Psychology will be securely based on the foundation . . ., of the necessary acquirement of each mental power and capacity by gradation. Much light will be thrown on the origin of man and his history.
For the materialists, this question of the origin of man became, in the words of Buechner, a matter of most intimate concern. In lectures he gave in Offenbach during the winter of 1866–67, he says:
Must the theory of transformation also be applied to our own race? Must it be extended to man, to us? Shall we have to submit to an application of the same principles or rules that have caused the life of all other organisms for the explanation of our own genesis and origin? Or are we—the lords of creation—an exception?
[ 17 ] Natural science clearly taught that man could not be an exception. On the basis of exact anatomical investigations the English physiologist, T. H. Huxley, wrote in his book, Man's Place in Nature (1863):
The critical comparison of all organs and their modification in the series of the monkeys leads us to one and the same result, that the anatomical differences that separate man from the gorilla and the chimpanzee are not as great as the differences that separate the anthropoid apes from the lower species of monkeys.
Could there still be a doubt in the face of such facts that natural evolution had also produced man—the same evolution that had caused the series of organic beings as far as the monkey through growth, propagation, inheritance, transmutation of forms and the struggle for life?
[ 18 ] During the course of the century this fundamental view penetrated more and more into the mainstream of natural science. Goethe, to be sure, had in his own way been convinced of this, and because of this conviction he had most energetically set out to correct the opinion of his contemporaries, which held that man lacked an intermaxillary bone in his upper jaw. All animals were supposed to have this bone; only man, so one thought, did not have it. In its absence one saw the proof that man was anatomically different from the animals, that the plan of his structure was to be thought along different lines. The naturalistic mode of Goethe's thinking inspired him to undertake elaborate anatomical studies to abolish this error. When he had achieved this goal he wrote in a letter to Herder, convinced that he had made a most important contribution to the knowledge of nature; “I compared the skulls of men and animals and I found the trail, and behold, there it is. Now I ask you not to tell, for it must be treated as a secret. But I want you to enjoy it with me, for it is like the finishing stone in the structure of man; now it is complete and nothing is lacking. Just see how it is!”
[ 19 ] Under the influence of such conceptions the great question of philosophy of man's relation to himself and to the external world led to the task of showing by the method of natural science what actual process had led to the formation of man in the course of evolution. Thereby the viewpoint from which one attempted to explain the phenomena of nature changed. As long as one saw in every organism including man the realization of a purposeful design of structure, one had to consider this purpose also in the explanation of organic beings. One had to consider that in the embryo the later organism is potentially indicated. When this view was extended to the whole universe, it meant that an explanation of nature fulfilled its task best if it showed how the later stages of evolution with man as the climax are prepared in the earlier stages.
[ 20 ] The modern idea of evolution rejected all attempts of science to recognize the potential later phases in the earlier stages. Accordingly, the later phase was in no way contained in the earlier one. Instead, what was gradually developed was the tendency to search in the later phases for traces of the earlier ones. This principle represented one of the laws of inheritance. One can actually speak of a reversal of the tendency of explanation. This reversal became important for ontogenesis, that is, for the formation of the ideas concerning the evolution of the individual being from the egg to maturity. Instead of showing the predisposition of the later organs in the embryo, one set out to compare the various stages that an organism goes through in the course of its individual evolution from the egg to maturity with those of other forms of organisms. Lorenz Oken was already moving in this direction. In the fourth volume of his General History of Nature for All Classes of Readers he wrote:
Years ago, through my physiological investigations, I arrived at the view that the developmental stages of the chicken in the egg have much similarity with different classes of animals. In the beginning it shows only the organs of infusoria, thereupon gradually assuming those of the polyps, jellyfish, shellfish, snails and so forth. Conversely, then, I also had to consider the classes of animals as evolutionary stages that proceeded parallel to the developmental stages of the chicken. This view of nature challenged me to the most minute observation of those organs that are added as new forms to every higher class of animal, as well as of the ones that are developed one after the other during the developmental process. It is, of course, not easy to establish a complete parallelism with such a difficult object as a chick egg because its development is so incompletely known. But to prove that the parallelism actually exists is indeed not difficult. It is most distinctly shown in the transformation of the insects, which is nothing more than the development of the young going on before our eyes outside the egg, and actually in so slow a tempo that we can observe and investigate every embryonic stage at our leisure.
Oken compares the stages of transformation of the insects with the other animals and finds that the caterpillars have a great similarity with worms, and the cocoons with crustaceous animals. From such similarities this ingenious thinker draws the conclusion that “there is, therefore, no doubt that we are here confronted with a conspicuous similarity that justifies the idea that the evolutionary history in the egg is nothing but a repetition of the history of the creation of the animal classes.” It came as a natural gift to this brilliant man to apprehend a great idea for which he did not even need the evidence of supporting facts. But it also lies in the nature of such subtle ideas that they have no great effect on those who work in the field of science. Oken appears like a comet on the firmament of German philosophy. His thought supplies a flood of light. From a rich treasure of ideas he suggests leading concepts for the most divergent facts. His method of formulating factual connections, however, was somewhat forced. He was too much preoccupied with the point he wanted to make. This attitude also prevailed in his treatment of the law of the repetition of certain animal forms in the ontogeny of others mentioned above.
[ 21 ] In contrast to Oken, Karl Ernst von Baer kept to the facts as firmly as possible when he spoke, in his History of the Evolution of Animals (1828), of the observations that had led Oken to his idea:
The embryos of the mammals, birds, lizards and snakes, and probably also those of the turtles, in their earlier stages are extraordinarily similar to one another in their whole formation as well as in their individual parts. These embryos are so similar in fact that they can often only be distinguished by their sizes. I have in my possession two little embryos in alcohol that I forgot to label, and now I cannot possibly determine to what class they belong. They could be lizards, little birds or young mammals, so similar is the head and trunk formation of these animals. The extremities are still completely absent in these embryos and, even if they were there, at the first stages of their development they would not tell us anything because the feet of lizards and mammals, the wings and feet of birds, as well as the hands and feet of men, all develop from the same original form.
Such facts of embryological development excited the greatest interest of those thinkers who tended toward Darwinism. Darwin had proven the possibility of change in organic forms and, through transformation, the species now in existence might possibly be descended from a few original forms, or perhaps only one. Now it was shown that in their first phases of development the various living organisms are so similar to each other that they can scarcely be distinguished from one another, if at all. These two ideas, the facts of comparative embryology and the idea of descent, were organically combined in 1864 by Fritz Müller (1821–97) in his thoughtful essay, Facts and Arguments for Darwin. Müller is one of those high-minded personalities who needs a naturalistic world conception because they cannot breathe spiritually without it. Also, in regard to his own action, he would feel satisfaction only when he could feel that his motivation was as necessary as a force of nature. In 1852 Müller settled in Brazil. For twelve years he was a teacher at the gymnasium in Desterro on the island of Santa Catharina, not far from the coast of Brazil. In 1867 he had to give up this position. The man of the new world conception had to give way to the reaction that, under the influence of the Jesuits, took hold of his school. Ernst Haeckel has described the life and activity of Fritz Müller in the Jenaische Zeitschrift fur Naturwissenschaft (Vol. XXXI N.F. XXIV 1897).
Darwin called Müller the “prince of observers,” and the small but significant booklet, Facts and Arguments for Darwin, is the result of a wealth of observations. It deals with a particular group of organic forms, the crustaceans, which are radically different from one another in their maturity but are perfectly similar at the time when they leave the egg. If one presupposes, in the sense of Darwin's theory of descent, that all crustacean forms have developed from one original type, and if one accepts the similarity in the early stages as an inherited element of the form of their common ancestor, one has thereby combined the ideas of Darwin with those of Oken pertaining to the repetition of the history of the creation of the animal species in the evolution of the individual animal form. This combination was accomplished by Fritz Müller. He thereby brought the earlier forms of an animal class into a certain law-determined connection with the later ones, which, through transformation, have formed out of them. The fact that at an earlier stage the ancestral form of a being now living has had a particular form caused its descendants at a later time to have another particular form. By studying the stages of the development of an organism one becomes acquainted with its ancestors whose nature has caused the characteristics of the embryonic forms. Phylogenesis and ontogenesis are, in Fritz Müller's book, connected as cause and effect. With this step a new element had entered the Darwinian trend of ideas. This fact retains its significance even though Müller's investigations of the crustaceans were modified by the later research of Arnold Lang.
[ 22 ] Only four years had passed since the appearance of Darwin's Origin of the Species when Müller's book was published as its defense and confirmation. Müller had shown how, with one special class of animals, one should work in the spirit of the new ideas. Then, in 1866, seven years after the Origin of the Species, a book appeared that completely absorbed this new spirit. Using the ideas of Darwinism on a high level of scientific discussion, it threw a great deal of light on the problems of the interconnection of all life phenomena. This book was Ernst Haeckel's General Morphology of Organisms. Every page reflected his attempt to arrive at a comprehensive synopsis of the totality of the phenomena of nature with the help of new thoughts. Inspired by Darwinism, Haeckel was in search of a world conception.
[ 23 ] Haeckel did his best in two ways to attempt a new world conception. First, he continually contributed to the accumulation of facts that throw light on the connection of the entities and energies of nature. Second, with unbending consistency he derived from these facts the ideas that were to satisfy the human need for explanation. He held the unshakable conviction that from these facts and ideas man can arrive at a fully satisfactory world explanation. Like Goethe, Haeckel was convinced in his own way that nature proceeds in its work “according to eternal, necessary and thereby divine laws, so that not even the deity could change it.” Because this was clear to him, he worshipped his deity in these eternal and necessary laws of nature and in the substances in which they worked. As the harmony of the natural laws, which are with necessity interconnected, satisfies reason, according to his view, so it also offers to the feeling heart, or to the soul that is ethically or religiously attuned, whatever it may thirst for. In the stone that falls to the ground attracted by gravity there is a manifestation of the same divine order that is expressed in the blossom of a plant and in the human spirit that created the drama of Wilhelm Tell.
[ 24 ] How erroneous is the belief that the feeling for the wonderful beauty of nature is destroyed by the penetration of reason into laws of nature is vividly demonstrated in the work of Ernst Haeckel. A rational explanation of nature had been declared to be incapable of satisfying the needs of the soul. Wherever man is disturbed in his inner life through knowledge of nature, it is not the fault of knowledge but of man himself. His sentiments are developed in a wrong direction. As we follow a naturalist like Haeckel without prejudice on his path as an observer of nature, we feel our hearts beat faster. The anatomical analysis, the microscopic investigation does not detract from natural beauty but reveals a great deal more of it. There is no doubt that there is an antagonism between reason and imagination, between reflection and intuition, in our time. The brilliant essayist, Ellen Key, is without doubt right in considering this antagonism as one of the most important phenomena of our time (compare Ellen Key, Essays, S. Fischer Verlag, Berlin, 1899). Whoever, like Ernst Haeckel, digs deep into the treasure mine of facts, boldly emerges with the thoughts resulting from these facts and climbs to the heights of human knowledge, can see in the explanation of nature only an act of reconciliation between the two contesting forces of reflection and intuition that “alternate in forcing each other into submission” (Ellen Key). Almost simultaneously with the publication of the book in which Haeckel presented with unflinching intellectual honesty his world conception derived from natural science, that is, with the appearance of his Riddles of the Universe in 1899, he began a serial publication called Artforms of Nature. In it he gives pictures of the inexhaustible wealth of wonderful formations that nature produces and that surpass “by far all artistic forms created by man” in beauty and in variety. The same man who introduces our mind to the law-determined order of nature leads our imagination to the beauty of nature.
[ 25 ] The need to bring the great problems of world conception into direct contact with scientific, specialized research led Haeckel to one of the facts concerning which Goethe said that they represent the significant points at which nature yields the fundamental ideas for its explanation of its own accord, meeting us halfway in our search. This was realized by Haeckel as he investigated how Oken's thesis, which Fritz Müller had applied to the crustaceans, could be fruitfully applied to the whole animal kingdom. In all animals except the Protista, which are one-celled organisms, a cup- or jug-shaped body, the gastrula, develops from the zygote with which the organism begins its ontogenesis. This gastrula is an animal form that is to be found in the first stages of development of all animals from the sponges to man. It consists merely of skin, mouth and stomach. There is a low class of zoophytes that possess only these organs during their lives and therefore resemble gastrulae. This fact is interpreted by Haeckel from the point of view of the theory of descent. The gastrula form is an inherited form that the animal owes to the form of its common ancestor. There had been, probably millions of years before, a species of animals, the gastrae, that was built in a way similar to that of the lower zoophytes still living today—the sponges, polyps, etc. From this animal species all the various forms living today, from the polyps, sponges, etc., to man, repeat this original form in the course of their ontogenies.
[ 26 ] In this way an idea of gigantic scope had been obtained. The path leading from the simple to the complicated, to the perfect form in the world of organisms, was thereby indicated in its tentative outline. A simple animal form develops under certain circumstances. One or several individuals of this form change to another form according to the conditions of life to which they are exposed. What has come into existence through this transmutation is again transmitted to descendants. There are then two different forms, the old one that has retained the form of the first stage, and a new one. Both of these forms can develop in different directions and into different degrees of perfection. After long periods of time an abundant wealth of species comes into existence through the transmission of the earlier form and through new formations by means of the process of adaptation to the conditions of life.
[ 27 ] In this manner Haeckel connects today's processes in the world of organisms with the events of primeval times. If we want to explain some organ of an animal of the present age, we look back to the ancestors that had developed this organ under the circumstances in which they lived. What has come into existence through natural causes in earlier times has been handed down to our time through the process of heredity. Through the history of the species the evolution of the individual receives its explanation. The phylogenesis, therefore, contains the causes for the ontogenesis. Haeckel expresses this fact in his fundamental law of biogenetics: “The short ontogenesis or development of the individual is a rapid and brief repetition, an abbreviated recapitulation of the long process of phylogenesis, the development of the species.”
[ 28 ] Through this law every attempt at explanation through special purposes, all teleology in the old sense, has been eliminated. One no longer looks for the purpose of an organ; one looks for the causes through which it has developed. A given form does not point to a goal toward which it strives, but toward the origin from which it sprang. The method of explanation for the organic phenomena has become the same as that for the inorganic. Water is not considered the aim of oxygen, nor is man considered the purpose of creation. Scientific research is directed toward the origin of, and the actual cause for, living beings. The dualistic mode of conception, which declares that the organic and the inorganic has to be explained according to two different principles, gives way to a monistic mode of conception, to a monism that has only one uniform mode of explanation for the whole of nature.
[ 29 ] Haeckel characteristically points out that through his discovery the method has been found through which every dualism in the above-mentioned sense must be overcome.
Phylogenesis is the mechanical cause of ontogenesis. With this statement our basically monistic conception of organic evolution is clearly characterized, and on the truth of this principle depends primarily the truth of the gastraea theory. . . . Every naturalist, who in the field of biogenesis is not satisfied with a mere admiration of strange phenomena but strives for an understanding of their significance, will, in the future, either have to side with or against this principle. It marks at the same time the complete break that separates the older teleological and dualistic morphology from the new mechanical and monistic one. If the physiological functions of inheritance and adaptation have been proven to be the only causes of the process of organic formation, then every kind of teleology, of dualistic and metaphysical mode of conception has thereby been eliminated from the field of biogenesis; the sharp contrast between the leading principles is clearly marked. Either a direct and causal connection between ontogeny and phylogeny exists or it does not. There is no third possibility! Either epigenesis and descent, or pre-formation and creation! (Compare alsoin Part 1 Chapter IX of this book.)
After Haeckel had absorbed Darwin's view of the origin of man he defended forcefully the conclusion that must be drawn from it. It was impossible for him just to hint hesitatingly, like Darwin, at this “problem of all problems.” Anatomically and physiologically man is not distinguishable from the higher animals. Therefore, the same origin must be attributed to him as to them. Haeckel boldly defended this opinion and the consequences that followed from it for the conception of the world. There was no doubt for him that in the future the highest manifestations of man's life, the activities of his spirit, were to be considered under the same viewpoint as the function of the simplest living organism. The observation of the lowest animals, the protozoa, infusoria, rhizopods, taught him that these organisms had a soul. In their motions, in the indications of the sensations they show, he recognized manifestations of life that only had to be increased and perfected in order to develop into man's complicated actions of reason and will.
[ 30 ] Beginning with the gastraea, which lived millions of years ago, what steps does nature take to arrive at man? This was the comprehensive question as stated by Haeckel. He supplied the answer in his Anthropogenesis, which appeared in 1874. In its first part, this book deals with the history of the individual (ontogenesis), in the second part, with that of the species (phylogenesis). He showed point by point how the latter contains the causes of the former. Man's position in nature had thereby been determined according to the principles of the theory of descent. To works like Haeckel's Anthropogenesis, the statement that the great anatomist, Karl Gegenbaur, made in his Comparative Anatomy (1870) can be justly applied. He wrote that in exchange for the method of investigation Darwin gave to science with his theory he received in return clarity and firmness of purpose. In Haeckel's view, the method of Darwinism had also supplied science with the theory of the origin of man.
[ 31 ] What actually was accomplished by this step can be appreciated in its full measure only if one looks at the opposition with which Haeckel's comprehensive application of the principles of Darwinism was received by the followers of idealistic world conceptions. It is not even necessary to quote those who, blindly believing in the traditional opinion, turned against the “monkey theory,” or those who believed that all finer, higher morality would be endangered if men were no longer convinced that they had a “purer, higher origin.” Other thinkers, although quite open-minded with regard to new truths, found it difficult to accept this new truth. They asked themselves the question, [ 32 ] “Do we not deny our own rational thinking if we no longer look for its origin in a general world reason over us, but in the animal kingdom below?” Mentalities of this sort eagerly attacked the points where Haeckel's view seemed to be without support of the facts. They had powerful allies in a number of natural scientists who, through a strange bias, used their factual knowledge to emphasize the points where actual experience was still insufficient to prove the conclusions drawn by Haeckel. The typical, and at the same time the most impressive, representative of this viewpoint of the naturalists was Rudolf Virchow (1821–1902). The opposition of Virchow and Haeckel can be characterized as follows. Haeckel puts his trust in the inner consistency of nature, concerning which Goethe is of the opinion that it is sufficient to make up for man's inconsistency. Haeckel, therefore, argues that if a principle of nature has been verified for certain cases, and if we still lack the experience to show its validity in other cases, we have no reason to hold the progress of our knowledge back. What experience denies us today, it may yield tomorrow. Virchow is of the opposite opinion. He wants to yield as little ground as possible to a comprehensive principle. He seems to believe that life for such a principle cannot be made hard enough. The antagonism between these two spirits was brought to a sharp point at the Fiftieth Congress of German naturalists and doctors in 1877. Haeckel read a paper there on the topic, The Theory of Evolution of Today in Its Relation to Science in General.
[ 33 ] In 1894 Virchow felt that he had to state his view in the following way. “Through speculation one has arrived at the monkey theory; one could just as well have ended up with an elephant theory or a sheep theory.” What Virchow demanded was incontestable proof of this theory. As soon as something turned up that fitted as a link in the chain of the argumentation, Virchow attempted to invalidate it with all means at his disposal.
[ 34 ] Such a link in the chain of proof was presented with the bone remnants that Eugen Dubois had found in Java in 1894. They consisted of a skull and thigh bone and several teeth. Concerning this find, an interesting discussion arose at the Congress of Zoologists at Leyden. Of twelve zoologists, three were of the opinion that these bones came from a monkey and three thought they came from a human being; six, however, believed they presented a transitional form between man and monkey. Dubois shows in a convincing manner in what relation the being whose bone remnants were under discussion stood to the present monkey, on the one hand, and to man of today, on the other. The theory of evolution of natural science must claim such intermediary forms. They fill the holes that exist between numerous forms of organisms. Every new intermediary form constitutes a new proof for the kinship of all living organisms. Virchow objected to the view that these bone remnants came from such an intermediary form. At first, he declared that it was the skull of a monkey and the thigh bone of a man. Expert paleontologists, however, firmly pronounced, according to the careful report, on the finding, that the remnants belonged together. Virchow attempted to support his view that the thigh bone could be only that of a human being with the statement that a certain growth in the bone proved that it must have had a disease that could only have been healed through careful human attention. The paleontologist, Marsch, [e.Ed: perhaps American paleontologist, Othniel Charles Marsh (1831–1899)] however, maintained that similar bone extuberances occurred in wild animals as well. A further statement of Virchow's, that the deep incision between the upper rim of the eye socket and the lower skull cover of the alleged intermediary form proved it to be the skull of a monkey was then contradicted by the naturalist Nehring, who claimed that the same formation was found in a human skull from Santos, Brazil. Virchow's objections came from the same turn of mind that also caused him to consider the famous skulls of Neanderthal, Spy, etc., as pathological formations, while Haeckel's followers regarded them as intermediary forms between monkey and man.
[ 35 ] Haeckel did not allow any objections to deprive him of his confidence in his mode of conception. He continued his scientific work without swerving from the viewpoints at which he had arrived, and through popular presentations of his conception of nature, he influenced the public consciousness. In his book, Systematic Phylogenesis, Outline of a Natural System of Organisms on the Basis of the History of Species (1894–96), he attempted to demonstrate the natural kinship of organisms in a strictly scientific method. In his Natural History of Creation, which, from 1868–1908, appeared in eleven editions, he gave a popular explanation of his views. In 1899, in his popular studies on monistic philosophy entitled, The Riddles of the Universe, he gave a survey of his ideas in natural philosophy by demonstrating without reserve the many applications of his basic thoughts. Between all these works he published studies on the most diverse specialized researches, always paying attention at the same time to the philosophical principles and the scientific knowledge of details.
[ 36 ] The light that shines out from the monistic world conception is, according to Haeckel's conviction, to “disperse the heavy clouds of ignorance and superstition that have heretofore spread an impenetrable darkness over the most important one of all problems of human knowledge, that is, the problem concerning man's origin, his true nature and his position in nature.” This is what he said in a speech given August 26, 1898 at the Fourth International Congress of Zoologists in Cambridge, On Our Present Knowledge Concerning the Origin of Man. In what respect his world conception forms a bond between religion and science, Haeckel has shown in an impressive way in his book, Monism as a Bond between Religion and Science, Credo of a Naturalist, which appeared in 1892.
[ 37 ] If one compares Haeckel with Hegel, one can see distinctly the difference in the tendencies of world conception in the two halves of the nineteenth century. Hegel lives completely in the idea and accepts only as much as he needs from the world of facts for the illustration of his idealistic world picture. Haeckel is rooted with every fiber of his being in the world of facts, and he derives from this world only those ideas toward which these facts necessarily tend. Hegel always attempts to show that all beings tend to reach their climax of evolution in the human spirit; Haeckel continuously endeavors to prove that the most complicated human activities point back to the simplest origins of existence. Hegel explains nature from the spirit; Haeckel derives the spirit from nature. We can, therefore, speak of a reversal of the thought direction in the course of the century. Within German intellectual life, Strauss, Feuerbach and others began this process of reversal. In their materialism the new direction found a provisional extreme expression, and in Haeckel's thought world it found a strictly methodical-scientific one. For this is the significant thing in Haeckel, that all his activity as a research worker is permeated by a philosophical spirit. He does not at all work toward results that for some philosophical motivation or other are considered to be the aim of his world conception or of his philosophical thinking. What is philosophical about him is his method. For him, science itself has the character of a world conception. His very way of looking at things predestines him to be a monist. He looks upon spirit and nature with equal love. For this reason he could find spirit in the simplest organism. He goes even further than that. He looks for the traces of spirit in the inorganic particles of matter:
Every atom possesses an inherent quantity of energy and in this sense is animate. Without assuming a soul for the atom, the simplest and most general phenomena of chemistry are unexplainable. Pleasure and displeasure, desire and aversion, attraction and repulsion must be a common property of all material atoms. For the motion of the atoms, which must take place in the formation and dissolution of every chemical compound can only be explained if we assume that they have sensation and will. On this assumption the generally accepted chemical doctrine of affinity is really based.
As he traces spirit down to the atom so he follows the purely material mechanism of events up to the most lofty accomplishments of the spirit:
The spirit and soul of man are also nothing else but energies that are inseparably bound to the material substratum of our bodies. As the motion of our flesh is bound to the form elements of our muscles, so our mind's power of thinking is bound to the form elements of our brains. Our spiritual energies are simply functions of these physical organs just as every energy is a function of a material body.
[ 38 ] One must not confuse this mode of conception with one that dreams souls in a hazy mystical fashion into the entities of nature and then assumes that they are more or less similar to that of man. Haeckel is a strict opponent of a world conception that projects qualities and activities of man into the external world. He has repeatedly expressed his condemnation of the humanization of nature, of anthropomorphism, with a clarity that cannot be misunderstood. If he attributes animation to inorganic matter, or to the simplest organisms, he means by that nothing more than the sum of energy manifestations that we observe in them. He holds strictly to the facts. Sensation and will are for him no mystical soul energies but are nothing more than what we observe as attraction and repulsion. He does not mean to say that attraction and repulsion are really sensation and will. What he means is that attraction and repulsion are on the lowest stage what sensation and will are on a higher one. For evolution is for him not merely an unwrapping of the higher stages of the spiritual out of the lower forms in which they are already contained in a hidden fashion, but a real ascent to new formations, an intensification of attraction and repulsion into sensation and will (compare prior comments in this Chapter).
This fundamental view of Haeckel agrees in a certain way with that of Goethe. He states in this connection that he had arrived at the fulfillment of his view of nature with his insight into the “two great springs of all nature,” namely, polarity and intensification (Polarität und Steigerung), polarity “belonging to matter insofar as we think of it materially, intensification insofar as we think of it spiritually. The former is engaged in the everlasting process of attraction and repulsion, the latter in a continual intensification. As matter can never be and act without spirit, however, nor spirit without matter, so matter can also be intensified and the spirit will never be without attraction and repulsion.”
[ 39 ] A thinker who believes in such a world conception is satisfied to explain by other such things and processes, the things and processes that are actually in the world. The idealistic world conceptions need, for the derivation of a thing or process, entities that cannot be found within the realm of the factual. Haeckel derives the form of the gastrula that occurs in the course of animal evolution from an organism that he assumes really existed at some time. An idealist would look for ideal forces under the influence of which the developing germ becomes the gastrula. Haeckel's monism draws everything he needs for the explanation of the real world from the same real world. He looks around in the world of the real in order to recognize in which way the things and processes explain one another. His theories do not have the purpose for him, as do those of the idealist, to find a higher element in addition to the factual elements, but they merely serve to make the connection of the facts understandable. Fichte, the idealist, asked the question of man's destination. He meant by that something that cannot be completely presented in the form of the real, the factual; something that reason has to produce as an addition to the factually given existence, an element that is to make the real existence of man translucent by showing it in a higher light. Haeckel, the monistic contemplator of the world, asks for the origin of man, and he means by that the factual origin, the lower organism out of which man had developed through actual processes.
[ 40 ] It is characteristic that Haeckel argues for the animation of the lower organisms. An idealist would have resorted to rational conclusions. He would present necessities of thought. Haeckel refers to what he has seen.
Every naturalist, who, like me, has observed for many years the life activities of the one-celled protozoa, is positively convinced that they, too, possess a soul. This cellular soul consists also of a sum of sensations, perceptions and will activities; sensation, thinking and will of our human souls differ from those of the cellular soul only in degree.
The idealist attributes spirit to matter because he cannot accept the thought that spirit can develop from mere matter. He believes that one would have to deny the spirit if one does not assume it to exist before its appearance in forms of existence without organs, without brains. For the monist, such thoughts are not possible. He does not speak of an existence that is not manifested externally as such. He does not attribute two kinds of properties to things: those that are real and manifested in them and those that in a hidden way are latent in them only to be revealed at a higher stage of development. For him, there is what he observes, nothing else, and if the object of observation continues its evolution and reaches a higher stage in the course of its development, then these later forms are there only in the moment when they become visible.
[ 41 ] How easily Haeckel's monism can be misunderstood in this direction is shown by the objections that were made by the brilliant thinker, Bartholomaeus von Carneri (1821–1909), who made lasting contributions for the construction of an ethics of this world conception. In his book, Sensations and Consciousness, Doubts Concerning Monism (1893), he remarks that the principle, “No spirit without matter, but also no matter without spirit,” would justify our extending this question to the plant and even to the next rock we may stumble against, and to attribute spirit also to them. Without doubt such a conclusion would lead to a confusion of distinctions. It should not be overlooked that consciousness arises only through the cell activity in the cerebrum. “The conviction that there is no spirit without matter, that is to say, that all spiritual activity is bound to a material activity, the former terminating with the latter, is based on experience, while there is no experience for the statement that there is always spirit connected with matter.” Somebody who would want to attribute animation to matter that does not show any trace of spirit would be like one who attributed the function to indicate time not to the mechanism of a watch but to the metal out of which it is made.
[ 42 ] Properly understood, Haeckel's view is not touched by Carneri's criticism. It is safe from this criticism because Haeckel holds himself strictly within the bounds of observation. In his Riddles of the Universe, he says, “I, myself, have never defended the theory of atom-consciousness. I have, on the contrary, expressly emphasized that I think the elementary psychic activities of sensation and will, which are attributed to the atoms, as unconscious.” What Haeckel wants is only that one should not allow a break in the explanation of natural phenomena. He insists that one should trace back the complicated mechanism by which spirit appears in the brain, to the simple process of attraction and repulsion of matter.
Haeckel considers the discovery of the organs of thought by Paul Flechsig to be one of the most important accomplishments of modern times. Flechsig had pointed out that in the gray matter of the brain there are to be found the four seats of the central sense organs, or four “inner spheres of sensation,” the spheres of touch, smell, sight and hearing. “Between the sense centers lie thought centers, the ‘real organs of mental life.’ They are the highest organs of psychic activity that produce thought and consciousness. . . . These four thought centers, distinguished from the intermediate sense centers by a peculiar and highly elaborate nerve structure, are the true organs of thought, the only organs of our consciousness. Recently, Flechsig has proved that man has some especially complicated structures in some of these organs that cannot be found in the other mammals and that explain the superiority of human consciousness.” (Riddles of the Universe, Chapt. X.)
[ 43 ] Passages like these show clearly enough that Haeckel does not intend to assume, like the idealistic philosophers, the spirit as implicitly contained in the lower stages of material existence in order to be able to find it again on the higher stages. What he wanted to do was to follow the simplest phenomena to the most complicated ones in his observation, in order to show how the activity of matter, which in the most primitive form is manifested in attraction and repulsion, is intensified in the higher mental operations.
[ 44 ] Haeckel does not look for a general spiritual principle for lack of adequate general laws explaining the phenomena of nature and mind. So far as his need is concerned, his general law is indeed perfectly sufficient. The law that is manifested in the mental activities seems to him to be of the same kind as the one that is apparent in the attraction and repulsion of material particles. If he calls atoms animated, this has not the same meaning that it would have if a believer in an idealistic world conception did so. The latter would proceed from the spirit. He would take the conceptions derived from the contemplation of the spirit down into the simplest functions of the atoms when he thinks of them as animated. He would explain thereby the natural phenomena from entities that he had first projected into them. Haeckel proceeds from the contemplation of the simplest phenomena of nature and follows them up to the highest spiritual activities. This means that he explains the spiritual phenomena from laws that he has observed in the simplest natural phenomena.
[ 45 ] Haeckel's world picture can take shape in a mind whose observation extends exclusively to natural processes and natural entities. A mind of this kind will want to understand the connection within the realm of these events and beings. His ideal would be to see what the processes and beings themselves reveal with respect to their development and interaction, and to reject rigorously everything that might be added in order to obtain an explanation of these processes and activities. For such an ideal one is to approach all nature as one would, for instance, proceed in explaining the mechanism of a watch. It is quite unnecessary to know anything about the watchmaker, about his skill and about his thoughts, if one gains an insight into the mechanical actions of its parts. In obtaining this insight one has, within certain limits, done everything that is admissible for the explanation of the operation of the watch. One ought to be clear about the fact that the watch itself cannot be explained if another method of explanation is admitted, as, for instance, if somebody thought of some special spiritual forces that move the hour and minute hands according to the course of the sun. Every suggestion of a special life force, or of a power that works toward a “purpose” within the organisms, appears to Haeckel as an invented force that is added to the natural processes. He is unwilling to think about the natural processes in any other way than by what they themselves disclose to observation. His thought structure is to be derived directly from nature.
In observing the evolution of world conception, this thought structure strikes us, as it were, as the counter-gift from the side of natural science to the Hegelian world conception, which accepts in its thought picture nothing from nature but wants everything to originate from the soul. If Hegel's world conception said that the self-conscious ego finds itself in the experience of pure thought, Haeckel's view of nature could reply that the thought experience is a result of the nature processes, is, indeed, their highest product. If the Hegelian world conception would not be satisfied with such a reply, Haeckel's naturalistic view could demand to be shown some inner thought experience that does not appear as if it were a mirror reflection of events outside thought life. In answer to this demand, a philosophy would have to show how thought can come to life in the soul and can really produce a world that is not merely the intellectual shadow of the external world. A thought that is merely thought, merely the product of thinking, cannot be used as an effective objection to Haeckel's view. In the comparison mentioned above, he would maintain that the watch contains nothing in itself that allows a conclusion as to the personality, etc., of the watchmaker. Haeckel's naturalistic view tends to show that, as long as one is merely confronted with nature, one cannot make any statement concerning nature except what it records. In this respect this naturalistic conception is significant as it appears in the course of the development of world conception. It proves that philosophy must create a field for itself that lies in the realm of spontaneous creativity of thought life beyond the thoughts that are gained from nature.
Philosophy must take the step beyond Hegel that was pointed out in a previous chapter. It cannot consist of a method that moves in the same field with natural science. Haeckel himself probably felt not the slightest need to pay any attention to such a step of philosophy. His world conception does bring thoughts to life in the soul, but only insofar as their life has been stimulated by the observation of natural processes. The world picture that thought can create when it comes to life in the soul without this stimulus represents the kind of higher world conception that would adequately complement Haeckel's picture of nature. One has to go beyond the facts that are directly contained in the watch if one wants to know, for instance, something about the form of the watchmaker's face. But, for this reason, one has no right to demand that Haeckel's naturalistic view itself should not speak as Haeckel does when he states what positive facts he has observed concerning natural processes and natural beings.
Darwinismus und Weltanschauung
[ 1 ] Sollte der Zweckmäßigkeitsgedanke eine Reform im Sinne einer naturgemäßen Weltanschauung erfahren, so mußten die zweckmäßigen Gebilde der belebten Natur in derselben Art erklärt werden, wie der Physiker, der Chemiker die unbelebten Vorgänge erklären. Wenn ein Magnetstab Eisenspäne an sich zieht, so denkt kein Physiker daran, daß in dem Stab eine auf das Ziel, den Zweck des Anziehens hinarbeitende Kraft wirke. Wenn Wasserstoff und Sauerstoff zu Wasser sich verbinden, so deutet das der Chemiker nicht so, als wenn in den beiden Materien etwas wirkte, dem der Zweck der Wasserbildung vorschwebt. Eine von eben solcher naturgemäßen Sinnesart beherrschte Erklärung der Lebewesen muß sich sagen: Die Organismen werden zweckmäßig, ohne daß etwas in der Natur auf diese Zweckmäßigkeit abzielt. Die Zweckmäßigkeit entsteht, ohne daß sie irgendwo als solche veranlagt wäre. Eine solche Erklärung des Zweckmäßigen hat Charles Darwin gegeben. Er stellte sich auf den Standpunkt, anzuerkennen, daß nichts in der Natur das Zweckmäßige will. Es kommt für die Natur gar nicht in Betracht, ob das, was in ihr entsteht, zweckmäßig ist oder nicht. Sie bringt also wahllos das Unzweckmäßige und das Zweckmäßige hervor.
[ 2 ] Was ist überhaupt zweckmäßig? Doch das, was so eingerichtet ist, daß seinen Bedürfnissen, seinen Lebensbedingungen die äußeren Verhältnisse des Daseins entsprechen. Unzweckmäßig dagegen ist, bei dem solches nicht der Fall ist. Was wird geschehen, wenn bei der vollständigen Planlosigkeit der Natur von dem Zweckmäßigsten bis zu dem Unzweckmäßigsten alle Grade von mehr oder minder Zweckmäßigem entstehen? Jedes Wesen wird suchen, sein Dasein in Gemäßheit der gegebenen Verhältnisse zu gestalten. Dem Zweckmäßigen gelingt das ohne weiteres, dem mehr oder weniger Zweckmäßigen nur in geringem Grade. Nun kommt eines hinzu: die Natur ist keine sparsame Wirtin in bezug auf die Hervorbringung der Lebewesen. Die Zahl der Keime ist eine ungeheure. Dieser Überfülle in der Produktion der Keime steht nur ein beschränktes Maß der Mittel des Lebens gegenüber. Die Folge wird sein, daß diejenigen Wesen ein leichteres Spiel für ihre Entwickelung haben, die zweckmäßiger für die Aneignung der Lebensmittel gebildet sind. Strebt ein zweckmäßiger eingerichtetes neben einem unzweckmäßiger eingerichteten Wesen nach Erhaltung seines Daseins, so wird das Zweckmäßigere dem Unzweckmäßigeren den Rang ablaufen. Das Letzte muß neben dem Ersten zugrunde gehen. Das Tüchtige, das heißt das Zweckmäßige, erhält sich, das Untüchtige, das heißt das Unzweckmäßige, erhält sich nicht. Das ist der «Kampf ums Dasein». Er bewirkt, daß Zweckmäßiges sich erhält, auch wenn in der Natur wahllos das Unzweckmäßige neben dem Zweckmäßigen entsteht. Durch ein Gesetz, das so objektiv, so weisheitlos ist, wie nur ein mathematisches oder mechanisches Naturgesetz sein kann, erhält der Gang der Naturentwickelung die Tendenz zur Zweckmäßigkeit, ohne daß diese Tendenz irgendwie in die Natur gelegt wäre.
[ 3 ] Darwin wurde auf diesen Gedanken durch das Werk des Nationalökonomen Malthus geführt «Über die Bedingungen und die Folgen der Volksvermehrung». In diesem ist ausgeführt, daß innerhalb der menschlichen Gesellschaft ein unaufhörlicher Wettkampf stattfindet, weil die Bevölkerung in viel rascherem Maße wächst als die Nahrungsmittelmenge. Dieses hier für die Menschheitsgeschichte aufgestellte Gesetz verallgemeinerte Darwin zu einem umfassenden Gesetz der ganzen Lebewelt.
[ 4 ] Darwin wollte nun zeigen, wie dieser Kampf ums Dasein zum Schöpfer der mannigfaltigen Formen lebender Wesen wird, wie durch ihn der alte Linnésche Grundsatz umgestoßen wird, daß wir «Spezies im Tier- und Pflanzenreich so viele zählen, als verschiedene Formen im Prinzip geschaffen sind». Die Zweifel an diesem Grundsatz bildeten sich bei Darwin klar aus, als er sich im Sommer 1831 auf einer Reise nach Südamerika und Australien befand. Er teilt mit, wie diese Zweifel bei ihm sich festsetzten: «Als ich während der Fahrt des Beagle den Galapagosarchipel, der im Stillen Ozean etwa fünfhundert englische Meilen von der südamerikanischen Küste entfernt liegt, besuchte, sah ich mich von eigentümlichen Arten von Vögeln, Reptilien und Schlangen umgeben, die sonst nirgends in der Welt existieren. Doch trugen sie fast alle amerikanisches Gepräge an sich. Im Gesang der Spottdrossel, in dem scharfen Geschrei des Aasgeiers, in den großen, leuchterähnlichen Opuntien bemerkte ich deutlich die Nachbarschaft mit Amerika; und doch waren diese Inseln durch so viele Meilen vom Festlande entfernt und wichen in ihrer geologischen Konstitution, in ihrem Klima weit von ihm ab. Noch überraschender war die Tatsache, daß die meisten Bewohner jeder einzelnen Insel dieses kleinen Archipels spezifisch verschieden waren, wenn auch untereinander nahe verwandt. Ich habe mich damals oft gefragt, wie diese eigentümlichen Tiere und Menschen entstanden seien. Die einfachste Art schien zu sein, daß die Bewohner der verschiedenen Inseln voneinander abstammen und im Verlauf ihrer Abstammung Modifikationen erlitten hätten, und daß alle Bewohner des Archipels von denen des nächsten Festlandes, nämlich Amerika, von welchem die Kolonisation natürlich herrühren würde, abstammen. Es blieb mir aber lange ein unerklärliches Problem, wie der notwendige Modifikationsgrad erreicht worden sein könne.» In der Antwort auf dieses Wie liegt die naturgemäße Auffassung der Entwickelung des Lebendigen. Wie der Physiker einen Stoff in verschiedene Verhältnisse bringt, um seine Eigenschaften kennen zu lernen, so beobachtete Darwin nach seiner Heimkehr die Erscheinungen, die sich am lebendigen Wesen in verschiedenen Verhältnissen ergeben. Er machte Züchtungsversuche mit Tauben, Hühnern, Hunden, Kaninchen und Kulturgewächsen. Durch sie zeigte sich, wie die lebenden Formen im Verlaufe ihrer Fortpflanzung sich fortwährend verändern. In gewissen Verhältnissen verändern sich gewisse Lebewesen nach wenigen Generationen so, daß man, falls man die neuentstandenen Formen mit ihren Ahnen vergleicht, von zwei ganz verschiedenen Spezies sprechen könnte, von denen jede nach einem eigenen Organisationsplan sich richtet. Solche Veränderlichkeit der Formen benutzt der Züchter, um Kulturorganismen zur Entwickelung zu bringen, die gewissen Absichten entsprechen. Er kann eine Schafsorte mit besonders feiner Wolle züchten, wenn er nur diejenigen Individuen seiner Herde sich fortpflanzen läßt, die die feinste Wolle haben. Innerhalb der Nachkommenschaft sucht er wieder die Individuen heraus, die mit der feinsten Wolle ausgestattet sind. Die Feinheit der Wolle steigert sich dann im Laufe der Generationen. Man erlangt nach einiger Zeit eine Schafspezies, die in der Bildung der Wolle sich sehr weit von ihren Vorfahren entfernt. Ein Gleiches ist bei anderen Eigenschaften der Lebewesen der Fall. Es folgt zweierlei aus dieser Tatsache. Einmal, daß in der Natur die Tendenz liegt, die Lebewesen zu wandeln; und dann, daß eine Eigenschaft, die nach einer gewissen Richtung sich zu wandeln angefangen hat, sich nach dieser Richtung steigert, wenn bei der Fortpflanzung der Lebewesen diejenigen Individuen ferngehalten werden, welche diese Eigenschaft noch nicht haben. Die organischen Formen nehmen also im Laufe der Zeit andere Eigenschaften an und halten sich in der Richtung ihrer einmal eingeschlagenen Verwandlung. Sie verwandeln sich und vererben gewandelte Eigenschaften. auf ihre Nachkommen.
[ 5 ] Die natürliche Folgerung aus dieser Beobachtung ist, daß Wandlung und Vererbung zwei in der Entwickelung der Lebewesen treibende Prinzipien sind. Nimmt man nun an, daß in naturgemäßer Weise in der Welt die Wesen sich so wandeln, daß Zweckmäßiges neben Unzweckmäßigem und mehr oder minder Zweckmäßigem entsteht, so muß man auch einen Kampf der mannigfaltigen gewandelten Formen voraussetzen. Dieser Kampf bewirkt planlos, was der Züchter planvoll macht. Wie dieser diejenigen Individuen von der Fortpflanzung ausschließt, die in die Entwickelung dasjenige hineinbringen würden, was. er nicht will, so beseitigt der Kampf ums Dasein das Unzweckmäßige. Es bleibt nur das Zweckmäßige für die Entwickelung. In diese wird dadurch, wie ein mechanisches Gesetz, die Tendenz zur steten Vervollkommnung gelegt. Darwin durfte, nachdem er dieses erkannt und damit der naturgemäßen Weltanschauung ein sicheres Fundament gelegt hatte, an das Ende seines eine neue Epoche des Denkens einleitenden Werkes «Die Entstehung der Arten» die enthusiastischen Worte setzen: «Aus dem Kampf der Natur, aus Hunger und Tod geht daher das Höchste, was wir zu erfassen vermögen, die Produktion der höheren Tiere hervor. Es liegt etwas Großartiges in dieser Ansicht vom Leben, wonach es mit allen seinen verschiedenen Kräften von dem Schöpfer aus wenig Formen, oder vielleicht nur einer, ursprünglich erschaffen wurde; und daß, während dieser Planet gemäß den bestimmten Gesetzen der Schwerkraft im Kreise sich bewegt, aus einem schlichten Anfang eine endlose Zahl der schönsten und wundervollsten Formen entwickelt wurden und noch entwickelt werden.» Zugleich ist aus diesem Satze zu ersehen, daß Darwin nicht durch irgendwelche antireligiöse Empfindungen, sondern allein aus den Folgerungen heraus, die sich ihm aus den deutlich sprechenden Tatsachen ergeben haben, zu seiner Anschauung gelangt ist. Bei ihm war es gewiß nicht der Fall, daß Feindseligkeit gegen die Bedürfnisse des Gefühls ihn zu einer vernünftigen Naturansicht bestimmte, denn er sagt uns in seinem Buche deutlich, wie die gewonnene Ideenwelt zu seinem Herzen spricht: «Sehr hervorragende Schriftsteller scheinen von der Ansicht, daß jede der Arten unabhängig erschaffen wurde, völlig befriedigt zu sein. Meiner Meinung nach stimmt es besser mit den, soweit wir es wissen, der Materie vom Schöpfer eingeprägten Gesetzen überein, daß das Hervorbringen und Erlöschen der früheren und jetzigen Bewohner der Erde, ebenso wie die Bestimmungen über Geburt und Tod eines Individuums, von sekundären Ursachen abhängig sind. Betrachte ich alle Wesen nicht als Sonderschöpfungen, sondern als lineare Abkömmlinge einiger weniger Wesen, die schon lange, bevor die jüngeren geologischen Schichten abgelagert waren, lebten, so scheinen sie mir dadurch veredelt zu sein ... Wir dürfen vertrauensvoll einer Zukunft von großer Länge entgegensehen. Und da die natürliche Zuchtwahl nur durch und für das Gute jedes Wesens wirkt, so werden alle körperlichen und geistigen Begabungen der Vollkommenheit zustreben.»
[ 6 ] An einer Fülle von Tatsachen zeigte Darwin, wie die Organismen wachsen und sich fortpflanzen, wie sie im Verlaufe ihrer Fortentwickelung einmal angenommene Eigenschaften vererben, wie neue Organe entstehen und sich durch Gebrauch oder Nichtgebrauch wandeln, wie sich also die Geschöpfe an ihre Daseinsbedingungen anpassen; und endlich wie der Kampf ums Dasein eine natürliche Auswahl (Zuchtwahl) trifft, wodurch mannigfaltige, immer vollkommenere Formen entstehen .
[ 7 ] Damit scheint eine Erklärung zweckmäßiger Wesen gefunden, die es nicht nötig macht, in der organischen Natur anders zu verfahren als in der unorganischen Solange man eine solche Erklärung nicht geben konnte, mußte man, wenn man folgerichtig sein wollte, zugeben, daß überall da, wo innerhalb der Natur ein Zweckmäßiges entsteht, eine der Natur fremde Macht eingreift. Damit war im Grunde für jeden solchen Fall ein Wunder zugegeben.
[ 8 ] Diejenigen, die sich jahrzehntelang vor dem Erscheinen des Darwinschen Werkes um eine naturgemäße Welt- und Lebensansicht bemühten, empfanden nunmehr in der allerlebhaftesten Weise, daß eine neue Richtung des Denkens gegeben war. Eine solche Empfindung hat 1872 David Friedrich Strauß in seinem «Alten und neuen Glauben» mit den Worten zum Ausdruck gebracht: «Man sieht, dahin ... muß es gehen, wo die Fähnlein lustig im Winde flattern. Ja lustig, und zwar im Sinne der reinsten erhabensten Geistesfreude. Wir Philosophen und kritischen Theologen haben gut reden gehabt, wenn wir das Wunder in Abgang dekretierten; unser Machtspruch verhallte ohne Wirkung, weil wir es nicht entbehrlich zu machen, keine Naturkraft nachzuweisen wußten, die es an den Stellen, wo es bisher am meisten für unerläßlich galt, ersetzen konnte. Darwin hat diese Naturkraft, dieses Naturverfahren nachgewiesen, er hat die Tür geöffnet, durch welche eine glücklichere Nachwelt das Wunder auf Nimmerwiederkehr hinauswerfen wird. Jeder, der weiß, was am Wunder hängt, wird ihn dafür als einen der größten Wohltäter des menschlichen Geschlechts preisen.»
[ 9 ] Durch Darwins Zweckmäßigkeitsidee ist es möglich, den Begriff der Entwickelung wirklich in naturgesetzlicher Weise zu denken. Der alten Einschachtelungslehre, die annimmt, daß alles, was entsteht, in verborgener Form schon früher vorhanden war (vgl. Seite 286 des ersten Bandes dieses Buches), waren damit ihre letzten Hoffnungen geraubt. Innerhalb eines im Sinne Darwins gedachten Entwickelungsvorgangs ist das Vollkommene in keiner Weise in dem Unvollkommenen schon enthalten. Denn die Vollkommenheit eines höheren Wesens entsteht durch Vorgänge, die mit den Vorfahren dieses Wesens schlechterdings gar nichts zu tun haben. Man denke: eine gewisse Entwickelungsreihe sei bei den Beuteltieren angelangt. In der Form der Beuteltiere liegt nichts, rein gar nichts von einer höheren, vollkommeneren Form. Es liegt in ihr nur die Fähigkeit, sich im weiteren Verlaufe ihrer Fortpflanzung wahllos zu verwandeln. Es treten nun Verhältnisse ein, die von jeder «inneren» Entwickelungsanlage der Beuteltierform unabhängig sind, die aber solche sind, daß sich von allen möglichen Wandelformen aus den Beuteltieren die Halbaffen erhalten. Es war in der Beuteltierform so wenig die Halbaffenform enthalten, wie in der Richtung einer rollenden Billardkugel der Weg enthalten ist, den sie einschlägt, nachdem sie von einer zweiten Kugel gestoßen worden ist.
[ 10 ] Denen, die an eine idealistische Denkweise gewöhnt waren, wurde die Auffassung dieses reformierten Entwickelungsbegriffes nicht leicht. Der aus Hegels Schule hervorgegangene, äußerst scharfsinnige und feine Geist Friedrich Theodor Vischer schreibt noch 1874 in einem Aufsatze: «Entwickelung ist ein Herauswickeln aus einem Keime, welches von Versuch zu Versuch fortschreitet, bis das Bild, das als Möglichkeit im Keime lag, wirklich geworden ist, dann aber stillstehend die gefundene Form als bleibende festhält. Überhaupt jeder Begriff kommt ins Schwanken, wenn wir die Typen, die nun seit so vielen Jahrtausenden auf unserem Planeten bestehen, und vor allem, wenn wir unseren eigenen Menschentypus für immer noch veränderlich halten sollen. Wir können dann unseren Gedanken, ja unseren Denkgesetzen, unseren Gefühlen, den Idealbildern unserer Phantasie, die doch nichts anderes sind als läuternde Nachbildungen von Formen der uns bekannten
[ 11 ] Natur: wir können keinem dieser festen Halte unserer Seele mehr trauen. Alles ist in Frage gestellt.» Und an einer anderen Stelle desselben Aufsatzes lesen wir: «Es wird mir zum Beispiel immer noch etwas schwer, zu glauben, daß man das Auge vom Sehen, das Ohr vom Hören bekomme. Das ungemeine Gewicht, das auf die Zuchtwahl gelegt wird, will mir auch nicht einleuchten.»
[ 12 ] Wenn Vischer gefragt worden wäre, ob er sich vorstellt, daß im Wasserstoff und Sauerstoff ein Bild des Wassers im Keime liege, damit dieses sich aus ihnen herausentwickeln könne, so würde er ohne Zweifel geantwortet haben: Nein; weder im Sauerstoff noch im Wasserstoff liegt etwas vom Wasser; die Bedingungen zur Entstehung dieses Stoffes sind erst in dem Augenblicke vorhanden, in dem Wasserstoff und Sauerstoff unter gewissen Verhältnissen zusammentreten. Braucht es nun anders zu sein, wenn aus dem Zusammenwirken der Beuteltiere mit den äußeren Daseinsbedingungen die Halbaffen entstehen ? Warum sollen die Halbaffen schon als Möglichkeit als, Bild in den Beuteltieren verborgen liegen, damit sie sich aus ihnen herausentwickeln können? Was durch Entwickelung entsteht, entsteht neu, ohne daß es vorher in irgendeiner Form vorhanden gewesen ist.
[ 13 ] Besonnene Naturforscher empfanden das Gewicht der neuen Zweckmäßigkeitslehre nicht weniger als Denker wie Strauß. Ohne Zweifel gehört Hermann Helmholtz zu denen, die in den fünfziger und sechziger Jahren als Repräsentanten solcher besonnenen Naturforscher gelten konnten. Er betont, wie die wunderbare und vor der wachsenden Wissenschaft immer reicher sich entfaltende Zweckmäßigkeit im Aufbau und in den Verrichtungen der Lebewesen geradezu herausfordert die Lebensvorgänge mit menschlichen Handlungen zu vergleichen. Denn diese sind die einzige Reihe von Erscheinungen, die einen ähnlichen Charakter wie die organischen Phänomene tragen. Ja, die zweckmäßigen Einrichtungen in der Qrganismenwelt übersteigen für unser Beurteilungsvermögen zumeist das weit, was menschliche Intelligenz zu schaffen vermag. Es ist also nicht zu verwundern, wenn man darauf verfallen ist, Bau und Tätigkeit der Lebewelt menschlichen weit überlegene Intelligenz zurückzuführen. «Man mußte daher» - sagt Helmholtz - «vor Darwin nur zwei Erklärungen der organischen Zweckmäßigkeit zugeben, welche aber beide auf Eingriffe freier Intelligenz in den Ablauf der Naturerscheinungen zurückführten. Entweder betrachtete man, der vitalistischen Theorie gemäß, die Lebensprozesse als fortdauernd geleitet durch eine Lebensseele; oder man griff für jede lebende Spezies auf einen Akt übernatürlicher Intelligenz zurück, durch den sie entstanden sein sollte ... Darwins Theorie enthält einen wesentlich neuen schöpferischen Gedanken. Sie zeigt, wie eine Zweckmäßigkeit der Bildung in den Organismen auch ohne alle Einmischung von Intelligenz durch das blinde Walten eines Naturgesetzes entstehen kann. Es ist dies das Gesetz der Forterbung der individuellen Eigentümlichkeiten von den Eltern auf die Nachkommen; ein Gesetz, was längst bekannt und anerkannt war und nur eine bestimmte Abgrenzung zu erhalten brauchte.» Helmholtz ist nun der Ansicht, daß durch das Prinzip der natürlichen Zuchtwahl im Kampf ums Dasein eine solche Abgrenzung des Gesetzes gegeben worden sei.
[ 14 ] Und ein Forscher, der nicht weniger als Helmholtz zu den vorsichtigsten gehörte, J. Henle, führt in einem Vortrag aus: «Sollten die Erfahrungen der künstlichen Züchtung auf die Oken-Lamarcksche Hypothese Anwendung finden, so mußte gezeigt werden, wie die Natur es anfängt, um von sich aus die Veranstaltungen zu treffen, mittels deren der Experimentator sein Ziel erreicht. Dies ist die Aufgabe, welche Darwin sich gestellt und mit bewundernswertem Eifer und Scharfsinn verfolgt hat.»
[ 15 ] Die größte Begeisterung unter allen empfanden die Materialisten über Darwins Tat. Ihnen war ja längst klar, daß ein solcher Mann über kurz oder lang kommen mußte, der das aufgehäufte, nach einem leitenden Gedanken drängende Tatsachengebiet philosophisch beleuchtete. Nach ihrer Meinung konnte, nach Darwins Entdeckung, der Weltanschauung, für die sie sich eingesetzt hatten, der Sieg nicht ausbleiben.
[ 16 ] Darwin ist als Naturforscher an seine Aufgabe herangetreten. Er hat sich zunächst innerhalb der Grenzen eines solchen gehalten. Daß seine Gedanken auf die Grundfragen der Weltanschauung, auf das Verhältnis des Menschen zur Natur, ein helles Licht werfen können, das wird in seinem grundlegenden Buch nur gestreift: «In der Zukunft sehe ich ein offenes Feld für weit wichtigere Forschungen. Die Psychologie wird sich sicherlich auf ... die Grundlage stützen: die Notwendigkeit, jede geistige Kraft und Fähigkeit stufenweise zu erwerben. Viel Licht mag auch noch über den Ursprung des Menschen und seine Geschichte verbreitet werden.» Diese Frage nach dem Ursprung des Menschen wurde den Materialisten, nach Büchners Ausdruck, geradezu zur Herzensangelegenheit. Er sagte in den Vorlesungen, die er in dem Winter 1866/67 in Offenbach hielt: «Muß die Umwandlungstheorie auch auf unser eigenes Geschlecht, auf den Menschen oder auf uns selbst angewendet werden? Müssen wir uns gefallen lassen, daß dieselben Prinzipien oder Regeln, welche die übrigen Organismen in das Leben gerufen haben, auch für unsere eigene Entstehung und Herkunft gelten sollen? Oder machen wir - die Herren der Schöpfung - eine Ausnahme?»
[ 17 ] Die Naturwissenschaft lehrte deutlich, daß der Mensch keine Ausnahme machen könne. Auf Grund genauer anatomischer Untersuchungen konnte der englische Naturforscher Huxley 1863 in seinen «Zeugnissen für die Stellung des Menschen in der Natur» den Satz aussprechen: «Die kritische Vergleichung aller Organe und ihrer Modifikationen innerhalb der Affenreihe führt uns zu diesem einen und demselben Resultate, daß die anatomischen Verschiedenheiten, welche den Menschen vom Gorilla und Schimpansen trennen, nicht so groß sind, als die Unterschiede, welche diese Menschenaffen von den niedrigeren Affenarten scheiden.» Konnte man solchen Tatsachen gegenüber noch zweifeln, daß die naturgemäße Entwickelung, die durch Wachstum und Fortpflanzung, durch Erblichkeit, Veränderlichkeit der Formen und Kampf ums Dasein die Reihe der organischen Wesen bis zum Affen herauf hat entstehen lassen, zuletzt auf dem ganz gleichen Wege auch den Menschen erzeugt hat?
[ 18 ] Die Grundanschauung drang eben im Laufe des Jahrhunderts immer tiefer ein in den Bestand der naturwissenschaftlichen Erkenntnisse, von der Goethe - allerdings auf seine Art - durchdrungen war, und wegen welcher er mit aller Energie daran ging, die Meinung seiner Zeitgenossen zu berichtigen, daß dem Menschen in der oberen Kinnlade ein sogenannter Zwischenkieferknochen fehle. Alle Tiere sollen diesen Knochen haben, nur der Mensch nicht, dachte man. Und darin sah man den Beweis, daß der Mensch anatomisch von den Tieren sich unterscheide, daß. er, seinem Bauplan nach, anders gedacht sei. Die naturgemäße Denkart Goethes forderte von ihm, daß er zur Hinwegschaffung dieses Irrtums emsige anatomische Studien betrieb. Und als ihm sein Ziel gelungen war, schrieb er im Vollgefühl davon, daß er etwas getan, was der Erkenntnis der Natur im höchsten Maße förderlich sei, an Herder: «Ich verglich ... Menschen- und Tierschädel, kam auf die Spur, und siehe, da ist es! Nun bitt' ich dich, laß dich nichts merken; denn es muß geheim behandelt werden. Es soll dich auch recht herzlich freuen; denn es ist wie der Schlußstein zum Menschen, fehlt nicht, ist auch da! Aber wie!»
[ 19 ] Unter dem Einflusse solcher Vorstellungen wurde die große Weltanschauungsfrage nach dem Verhältnis des Menschen zu sich selbst und zur Außenwelt zu der Aufgabe, auf naturwissenschaftlichem Wege zu zeigen, welches die tatsächlichen Vorgänge sind, die im Laufe der Entwickelung zur Bildung des Menschen geführt haben. Damit änderte sich der Gesichtspunkt, von dem aus man die Naturerscheinungen zu erklären suchte. Solange man in jedem Organismus, und damit auch im Menschen, einen zweckmäßigen Bauplan verwirklicht sah, mußte man bei der Erklärung der Wesen diesen Zweck ins Auge fassen. Man mußte eben darauf Bedacht nehmen, daß im Embryo sich der spätere Organismus in der Anlage vorher verkündigt. Aufs ganze Weltall ausgedehnt, bedeutete dies, daß diejenige Naturerklärung ihre Aufgabe am besten erfülle, die zeigt, wie die Natur auf den früheren Stufen ihrer Entwickelung sich darauf vorbereitet, die späteren, und, auf dem Gipfel, den Menschen zu erzeugen.
[ 20 ] Die moderne Entwickelungsidee verwarf alle Neigung der Erkenntnis, in dem Früheren bereits das Spätere zu sehen. Für sie war ja in keiner Weise das Spätere im Früheren enthalten. Dagegen bildete sich in ihr immer mehr der Grundsatz aus, in dem Späteren das Frühere zu suchen. Dieser Grundsatz bildete ja ein Bestandstück des Prinzips der Vererbung. Man darf geradezu von einer Umkehrung der Richtung des Erklärungsbedürfnisses sprechen. Wichtig wurde diese Umkehrung für die Ausbildung der Gedanken über die Entwickelung des einzelnen organischen Individuums vom Ei bis zum reifen Zustande, für die sogenannte Keimesgeschichte (Ontogenie). Statt sich vorzuhalten, daß sich im Embryo die späteren Organe vorbereiten, ging man daran, die Formen, die der Organismus im Laufe seiner individuellen Entwickelung vom Ei bis zur Reife annimmt, mit anderen Organismenformen zu vergleichen. Schon Lorenz Oken verfolgte eine solche Spur. Er schrieb im vierten Band seiner «Allgemeinen Naturgeschichte für alle Stände» (S. 468): «Ich bin durch meine physiologischen Untersuchungen schon vor einer Reihe von Jahren auf die Ansicht gekommen, daß die Entwickelungszustände des Küchelchens im Ei Ähnlichkeit haben mit den verschiedenen Tierklassen, so daß es Anfangs gleichsam nur die Organe der Infusorien besitze, dann allmählich die der Polypen, Quallen, Muscheln, Schnecken usw. erhalte. Umgekehrt mußte ich dann auch die Tierklassen als Entwickelungsstufen betrachten, welche denen des Küchelchens parallel gingen. Diese Ansicht von der Natur forderte die genaueste Vergleichung derjenigen Organe, welche in einer jeden höheren Tierklasse neu zu den andern hinzukommen, und ebenso derjenigen, welche im Küchelchen sich während des Brütens nacheinander entwickeln. Ein vollkommener Parallelismus ist natürlich nicht so leicht bei einem so schwierigen und noch lange nicht hinlänglich beobachteten Gegenstande herzustellen. Zu beweisen aber, daß er wirklich vorhanden sei, ist in der Tat nicht schwer: dieses zeigt am deutlichsten die Verwandlung der Insekten, welche nichts weiter ist, als eine Entwickelung der Jungen, die außerhalb dem Ei vor unsern Augen vorgeht, und zwar so langsam, daß wir jeden embryonischen Zustand mit Muße betrachten und untersuchen können.» Oken vergleicht die Verwandlungszustände der Insekten mit anderen Tieren und findet, daß die Raupen die größte Ähnlichkeit mit den Würmern haben, die Puppen mit den Krebsen. Aus solchen Ähnlichkeiten schließt der geniale Denker: «Es ist daher kein Zweifel, daß hier eine auffallende Ähnlichkeit besteht, welche die Idee rechtfertigt, daß die Entwicklungsgeschichte im Ei nichts anderes sei, als eine Wiederholung der Schöpfungsgeschichte der Tierklassen.» Es lag in der Natur dieses geistvollen Mannes, eine große Idee auf Grund eines glücklichen Aperçus zu ahnen. Er brauchte zu einer solchen Ahnung nicht einmal die entsprechend vollrichtigen Tatsachen. Aber es liegt auch in der Natur solcher geahnten Ideen, daß sie auf die Arbeiter im Felde der Wissenschaft keinen großen Eindruck machen. Wie ein Komet blitzt Oken am deutschen Weltanschauungshimmel auf. Eine Fülle von Licht entwickelt er. Aus einem reichen Ideenbesitz heraus gibt er Leitbegriffe für die verschiedensten Tatsachengebiete. Doch hatte die Art, wie er sich Tatsachenzusammenhänge zurechtlegte, zumeist etwas Gewaltsames. Er arbeitete auf die Pointe los. Das war auch bei dem oben genannten Gesetze der Wiederholung gewisser Tierformen in der Keimentwickelung anderer der Fall.
[ 21 ] Im Gegensatz zu Oken hielt sich Carl Ernst von Baer möglichst an das rein Tatsächliche, als er 1828 in seiner «Entwickelungsgeschichte der Tiere» von dem sprach, was Oken zu seiner Idee geführt hat. «Die Embryonen der Säugetiere, Vögel, Eidechsen und Schlangen, wahrscheinlich auch der Schildkröten, sind in frühen Zuständen einander ungemein ähnlich im Ganzen sowie in der Entwickelung der einzelnen Teile; so ähnlich, daß man oft die Embryonen nur nach der Größe unterscheiden kann. Ich besitze zwei kleine Embryonen in Weingeist, für die ich versäumt habe, die Namen zu notieren; und ich bin jetzt durchaus nicht imstande, die Klasse zu bestimmen, der sie angehören. Es können Eidechsen, kleine Vögel oder ganz junge Säugetiere sein. So übereinstimmend ist Kopf- und Rumpfbildung in diesen Tieren. Die Extremitäten fehlen aber jenen Embryonen noch. Wären sie auch da, auf der ersten Stufe der Ausbildung begriffen, so würden sie doch nichts lehren, da die Füße der Eidechsen und Säugetiere, die Flügel und Füße der Vögel, sowie die Hände und Füße der Menschen sich aus derselben Grundform entwickeln.» Solche Tatsachen der Keimesgeschichte mußten bei denjenigen Denkern, die zum Darwinismus mit ihren Überzeugungen neigten, das größte Interesse hervorrufen. Darwin hatte die Möglichkeit erwiesen, daß die organischen Formen sich wandeln, und daß auf dem Wege der Umwandlung die heute lebenden Arten von wenigen, vielleicht nur von einer ursprünglichen abstammen. Nun zeigen sich die mannigfaltigen Lebewesen auf ihren ersten Entwickelungsstufen so ähnlich, daß man sie kaum oder gar nicht unterscheiden kann. Beides, diese Tatsache der Ähnlichkeit und jene Abstammungsidee, brachte 1864 Fritz Müller in einer gedankenvollen Schrift «Für Darwin» in organische Verbindung. Müller ist eine von denjenigen hochsinnigen Persönlichkeiten, deren Seelen eine naturgemäße Weltanschauung zum geistigen Atmen unbedingt brauchen. Er empfand auch an seinem eigenen Handeln allein Befriedigung, wenn er nur den Motiven gegenüber das Gefühl haben konnte, daß sie notwendig wie eine Naturkraft sind. Im Jahre 1852 übersiedelte Müller nach Brasilien. Er bekleidete zwölf Jahre lang eine Gymnasiallehrerstelle in Desterro (auf der Insel Santa Catharina unweit der Küste von Brasilien). 1867 mußte er auch diese Stellung aufgeben. Der Mann der neuen Weltanschauung mußte der Reaktion weichen, die sich unter dem Einflusse der Jesuiten seiner Lehranstalt bemächtigte. Ernst Haeckel hat in der «Jenaischen Zeitschrift für Naturwissenschaft» (XXXI. Band N. F. XXIV, 1897) das Leben und die Wirksamkeit Fritz Müllers beschrieben. Von Darwin wurde dieser als «Fürst der Beobachter» bezeichnet. Und aus einer Fülle von Beobachtungen heraus ist die kleine, aber bedeutungsvolle Schrift «Für Darwin» entstanden. Sie behandelte eine einzelne Gruppe von organischen Formen, die Krebse, in dem Geiste, von dem Fritz Müller glaubte, daß er sich aus der Darwinschen Anschauung ergeben müsse. Er zeigte, daß die in ihren reifen Zuständen voneinander verschiedenen Krebsformen einander vollkommen ähnlich sind in der Zeit, in der sie aus dem Ei schlüpfen. Setzt man voraus, daß im Sinne der Darwinschen Abstammungslehre die Krebsformen aus einer Ur-Krebsform sich entwickelt haben, und nimmt man an, daß die Ähnlichkeit in Jugendzuständen dieser Tiere ein Erbstück von ihrer gemeinsamen Ahnenform her ist, so hat man die Ideen Darwins vereinigt mit denen Okens von der Wiederholung der Schöpfungsgeschichte der Tierklassen in der Entwickelung der einzelnen Tierform. Diese Vereinigung hat Fritz Müller auch vollzogen. Er brachte dadurch die frühen Formen einer Tierklasse in eine bestimmte gesetzmäßige Verbindung mit den späteren, die sich durch Umwandlung aus ihnen gebildet haben. Daß einmal eine Ahnenform eines heute . lebenden Wesens so und so ausgesehen hat, das hat bewirkt, daß dieses heute lebende Wesen in einer Zeit seiner Entwickelung so und so aussieht. An den Entwickelungsstadien der Organismen erkennt man ihre Ahnen; und die Beschaffenheit der letzten bewirkt die Charaktere der Keimformen. Stammesgeschichte und Keimesgeschichte (Phylogenie und Ontogenie) sind in Fritz Müllers Buch verbunden wie Ursache und Wirkung. Damit war ein neuer Zug in die Darwinsche Ideenrichtung gekommen. Dieses wird auch dadurch nicht abgeschwächt, daß Müllers Krebsforschungen durch die späteren Untersuchungen Arnold Langs modifiziert wurden.
[ 22 ] Es waren erst vier Jahre vergangen seit dem Erscheinen von Darwins Buch «Entstehung der Arten», als Müllers Schrift zu seiner Verteidigung und Bestätigung erschien. Er hatte an einer einzelnen Tierklasse gezeigt, wie man im Geiste der neuen Ideen arbeiten soll. Sieben Jahre nach der «Entstehung der Arten», im Jahre 1866, erschien bereits ein Buch, das ganz durchdrungen von diesem neuen Geiste war, das von hoher Warte herab mit den Ideen des Darwinismus den Zusammenhang der Lebenserscheinungen beleuchtete: Ernst Haeckels «Generelle Morphologie der Organismen». Jede Seite dieses Buches verrät das große Ziel, von den neuen Gedanken aus eine Umschau über die Gesamtheit der Naturerscheinungen zu halten. Aus dem Darwinismus heraus suchte Haeckel eine Weltanschauung.
[ 23 ] Nach zwei Richtungen hin war Haeckel bestrebt, für die neue Weltanschauung das Möglichste zu tun: er bereicherte unablässig das Wissen von den Tatsachen, die Aufschluß geben über den Zusammenhang der Naturwesen und Naturkräfte; und er zog mit eiserner Konsequenz aus diesen Tatsachen die Ideen, die das menschliche Erklärungsbedürfnis befriedigen sollen. Er ist von der unerschütterlichen Überzeugung durchdrungen, daß der Mensch für alle seine Seelenbedürfnisse aus diesen Tatsachen und diesen Ideen volle Befriedigung gewinnen kann. Wie es Goethe auf seine Art klar war, so ist es auch ihm auf die seinige klar, daß die Natur «nach ewigen, notwendigen, dergestalt göttlichen Gesetzen wirkt, daß die Gottheit selbst daran nichts ändern könnte». Und weil ihm dieses klar ist, verehrt er in den ewigen und notwendigen Gesetzen der Natur und in den Stoffen, an denen sich diese Gesetze betätigen, seine Gottheit. Wie die Harmonie der in sich mit Notwendigkeit zusammenhängenden Naturgesetze, nach seiner Anschauung, die Vernunft befriedigt, so bietet sie auch dem fühlenden Herzen, dem ethisch und religiös gestimmten Gemüt, wonach dieses dürstet. In dem Stein, der von der Erde angezogen, zu dieser hinfällt, spricht sich das gleiche Göttliche aus wie in der Pflanzenblüte und in dem menschlichen Geiste, der den «Wilhelm Tell» dramatisch formt.
[ 24 ] Wie irrtümlich es ist, zu glauben, daß durch ein vernünftiges Eindringen in das Walten der Natur, durch Erforschung ihrer Gesetze, das Gefühl für die wunderbaren Schönheiten der Natur zerstört wird, das zeigt sich so recht anschaulich an dem Wirken Ernst Haeckels. Man hat der vernunftgemäßen Naturerklärung die Fähigkeit abgesprochen, die Bedürfnisse des Gemütes zu befriedigen. Es darf behauptet werden, daß, wo immer ein Mensch in seiner Gemütswelt durch die Naturerkenntnis beeinträchtigt wird, dies nicht an dieser Erkenntnis, sondern an dem Menschen liegt, dessen Empfindungen sich in einer falschen Richtung bewegen. Wer unbefangen den Forscherwegen eines Naturbetrachters, wie es Haeckel ist, folgt, der wird bei jedem Schritte in der Naturerkenntnis auch sein Herz höher schlagen fühlen. Die anatomische Zergliederung, die mikroskopische Untersuchung wird ihm keine Naturschönheit zerstören, aber unzählige neue enthüllen. Es ist zweifellos, daß in unserer Zeit ein Kampf besteht zwischen Verstand und Phantasie, zwischen Reflexion und Intuition. Ellen Key, die geistvolle Essayistin, hat unbedingt recht, wenn sie in diesem Kampfe eine der wichtigsten Erscheinungen in der gegenwärtigen Zeit sieht. (Vgl. Ellen Key: Essays. Berlin, 5. Fischers Verlag, 1899.) Wer, wie Ernst Haeckel, tief hinuntergräbt in den Schacht der Tatsachen und kühn hinaufsteigt mit den Gedanken, die uns aus diesen Tatsachen sich ergeben, zu den Gipfeln menschlicher Erkenntnis, der kann nur in der Naturerklärung die versöhnende Macht finden «zwischen den beiden gleich starken Rennern, der Reflexion und der Intuition, die sich wechselseitig in die Knie zwingen». (Ellen Key, ebd.) Fast gleichzeitig mit der Veröffentlichung, durch die Haeckel mit rückhaltloser Redlichkeit seine aus der Naturerkenntnis fließende Weltanschauung darlegt, mit dem 1899 erfolgten Erscheinen seiner «Welträtsel», hat er mit der Herausgabe eines Lieferungswerkes begonnen, «Kunstformen der Natur», in dem er Nachbildungen gibt von der unerschöpflichen Fülle der wunderbaren Gestalten, welche die Natur in ihrem Schoße erzeugt, und welche an Schönheit und Mannigfaltigkeit «alle vom Menschen geschaffenen Kunstformen weitaus» übertreffen. Derselbe Mann, der unseren Verstand in die Gesetzmäßigkeit der Natur führt, lenkt unsere Phantasie auf die Schönheit der Natur.
[ 25 ] Das Bedürfnis, die großen Weltanschauungsfragen in unmittelbare Berührung zu bringen mit den wissenschaftlichen Einzeluntersuchungen, hat Haeckel zu einer derjenigen Tatsachen geführt, von denen Goethe sagt, daß sie prägnante Punkte bezeichnen, an denen die Natur die Grundideen zu ihrer Erklärung freiwillig hergibt und uns entgegenträgt. Diese Tatsache bot sich für Haeckel dadurch, daß er untersuchte, inwiefern sich der alte Okensche Gedanke, den Fritz Müller auf die Krebstiere anwendete, für das ganze Tierreich fruchtbar machen lasse. Bei allen Tieren, mit Ausnahme der Protisten, die zeitlebens nur aus einer Zelle bestehen, bildet sich aus der Eizelle, mit der das Wesen seine Keimesentwickelung beginnt, ein becherförmiger oder krugförmiger Körper, der sogenannte Becherkeim oder die Gastrula. Dieser Becherkeim ist eine tierische Form, die alle Tiere, von den Schwämmen bis herauf zum Menschen, in ihrem ersten Entwickelungsstadium annehmen. Diese Form hat nur Haut, Mund und Magen. Nun gibt es niedere Pflanzentiere, die während ihres ganzen Lebens nur diese Organe haben, die also dem Becherkeim ähnlich sind. Diese Tatsache deutete Haeckel im Sinne der Entwickelungstheorie. Die Gastrulaform ist ein Erbstück, das die Tiere von ihrer gemeinsamen Ahnenform überkommen haben. Es hat eine wahrscheinlich vor Jahrmillionen ausgestorbene Tierart gegeben, die Gastraea, die ähnlich gebaut war wie die heute noch lebenden niederen Pflanzentiere: die Spongien, Polypen usw. Aus dieser Tierart hat sich alles entwickelt, was heute an mannigfaltigen Formen zwischen den Polypen, Schwämmen und Menschen lebt. Alle diese Tiere wiederholen im Verlaufe ihrer Keimesgeschichte diese ihre Stammform.
[ 26 ] Eine Idee von ungeheurer Tragweite war damit gewonnen. Der Weg vom Einfachen zum Zusammengesetzten, zum Vollkommenen in der Organismenwelt war vorgezeichnet. Eine einfache Tierform entwickelt sich unter gewissen Umständen. Eines oder mehrere Individuen dieser Form verwandeln sich nach Maßgabe der Lebensverhältnisse, in die sie kommen, in eine andere Form. Was durch Verwandlung entstanden ist, vererbt sich wieder auf Nachkommen. Es leben bereits zweierlei Formen. Die alte, die auf der ersten Stufe stehen geblieben ist, und eine neue. Beide Formen können sich nach verschiedenen Richtungen und Vollkommenheitsgraden weiterbilden. Nach großen Zeiträumen entsteht durch Vererbung der entstandenen Formen und durch Neubildungen auf dem Wege der Anpassung an die Lebensbedingungen eine Fülle von Arten.
[ 27 ] So schließt sich für Haeckel zusammen, was heute in der Organismenwelt geschieht, mit dem, was in Urzeiten geschehen ist. Wollen wir irgendein Organ an einem Tiere unserer Gegenwart erklären, so blicken wir zurück auf die Ahnen, die bei sich dieses Organ unter den Verhältnissen, in denen sie lebten, ausgebildet haben. Was in früheren Zeiten aus natürlichen Ursachen entstanden ist, hat sich bis heute vererbt. Durch die Geschichte des Stammes klärt sich die Entwickelung des Individuums auf. In der Stammesentwickelung (Phylogenesis) liegen somit die Ursachen der Individualentwickelung (Ontogenesis). Haeckel drückt diese Tatsache in seinem biogenetischen Grundgesetze mit den Worten aus, die kurze Ontogenesis oder die Entwickelung des Individuums ist eine schnelle und zusammengezogene Wiederholung, eine gedrängte Rekapitulation der langen Phylogenese oder Entwickelung der Art.
[ 28 ] Damit ist aus dem Reiche des Organischen alle Erklärung im Sinne besonderer Zwecke, alle Teleologie im alten Sinne, entfernt. Man sucht nicht mehr nach dem Zweck eines Organes, man sucht nach den Ursachen, aus denen es sich entwickelt hat; eine Form weist nicht nach dem Ziel hin, dem sie zustrebt, sondern nach dem Ursprunge, aus dem sie hervorgegangen ist. Die Erklärungsweise des Organischen ist der des Unorganischen gleich geworden. Man sucht das Wasser nicht als Ziel im Sauerstoff und man sucht auch nicht den Menschen als Zweck in der Schöpfung. Man forscht nach dem Ursprunge, nach den tatsächlichen Ursachen der Wesen. Die dualistische Anschauungsweise, die erklärt, daß Unorganisches und Organisches nach zwei verschiedenen Prinzipien erklärt werden müssen, verwandelt sich in eine monistische Vorstellungsart, in den Monismus, der für die ganze Natur nur eine einheitliche Erklärungsweise hat.
[ 29 ] Haeckel weist mit bedeutsamen Worten darauf hin, daß durch seine Entdeckung der Weg gefunden ist, auf dem aller Dualismus in dem oben gemeinten Sinne überwunden werden muß. «Die Phylogenesis ist die mechanische Ursache der Ontogenesis. Mit diesem einen Satz ist unsere prinzipielle monistische Auffassung der organischen Entwickelung klar bezeichnet, und von der Wahrheit dieses Grundsatzes hängt in erster Linie die Wahrheit der Gastraeatheorie ab... . Für und wider diesen Grundsatz wird in Zukunft jeder Naturforscher sich entscheiden müssen, der in der Biogenie sich nicht mit der bloßen Bewunderung merkwürdiger Erscheinungen begnügt, sondern darüber hinaus nach dem Verständnis ihrer Bedeutung strebt. Mit diesem Satz ist zugleich die unausfüllbare Kluft bezeichnet, welche die ältere teleologische und dualistische Morphologie von der neueren mechanischen und monistischen trennt. Wenn die physiologischen Funktionen der Vererbung und Anpassung als die alleinigen Ursachen der organischen Formbildung nachgewiesen sind, so ist damit zugleich jede Art von Teleologie, von dualistischer und metaphysischer Betrachtungsweise aus dem Gebiete der Biogenie entfernt; der scharfe Gegensatz zwischen den leitenden Prinzipien ist damit klar bezeichnet. Entweder existiert ein direkter und kausaler Zusammenhang zwischen Ontogenie und Phylogenie oder er existiert nicht. Entweder ist die Ontogenese ein gedrängter Auszug der Phylogenese oder sie ist dies nicht. Zwischen diesen beiden Annahmen gibt es keine dritte! Entweder Epigenesis und Deszendenz - oder Präformation und Schöpfung.» (Vgl. auch Band 1, S.286 ff. dieses Buches.) Haeckel ist eine philosophische Denkerpersönlichkeit. Deshalb trat er, bald nachdem er die Darwinsche Anschauung in sich aufgenommen hatte, mit aller Energie für die wichtige Schlußfolgerung ein, die sich aus dieser Anschauung für den Ursprung des Menschen ergibt. Er konnte sich nicht damit begnügen, schüchtern wie Darwin auf diese «Frage aller Fragen» hinzudeuten. Der Mensch unterscheidet sich anatomisch und physiologisch nicht von den höheren Tieren, folglich muß ihm auch der gleiche Ursprung wie diesen zugeschrieben werden. Mit großer Kühnheit trat er sogleich für diese Meinung und für alle Folgen ein, die sich in bezug auf die Weltanschauung daraus ergeben. Es war für ihn nicht zweifelhaft, daß fortan die höchsten Lebensäußerungen des Menschen, die Taten seines Geistes, unter einem gleichen Gesichtspunkt zu betrachten sind wie die Verrichtungen der einfachsten Lebewesen. Die Betrachtung der niedersten Tiere, der Urtiere, Infusorien und Rhizopoden, lehrte ihn, daß auch diese Organismen eine Seele haben. In ihren Bewegungen, in den Andeutungen von Empfindungen, die sie erkennen lassen, erkannte er Lebensäußerungen, die nur gesteigerter, vollkommener zu werden brauchen, um zu den komplizierten Vernunft- und Willenshandlungen des Menschen zu werden.
[ 30 ] Welche Schritte vollführt die Natur, um von der Gastraea, dem Urdarmtiere, das vor Jahrmillionen gelebt hat, zum Menschen zu gelangen? Das war die umfassende Frage, die sich Haeckel vorlegte. Die Antwort gab er in seiner 1874 erschienenen «Anthropogenie». Sie behandelt in einem ersten Teil die Keimesgeschichte des Menschen, und in einem zweiten die Stammesgeschichte. Von Punkt zu Punkt wurde gezeigt, wie in der letzteren die Ursachen für die erstere liegen. Die Stellung des Menschen in der Natur war damit nach den Grundsätzen der Entwickelungslehre bestimmt. Auf Werke, wie Haeckels «Anthropogenie» eines ist, darf man das Wort anwenden, daß der große Anatom Karl Gegenbaur in seiner «Vergleichenden Anatomie» (2. Aufl., 1870) ausgesprochen hat, daß der Darwinismus als Theorie reichlich das von der Wissenschaft zurückempfängt, was er dieser an Methode gegeben hat: Klarheit und Sicherheit. Mit der darwinistischen Methode ist für Haeckel auch die Theorie von der Herkunft des Menschen der Wissenschaft geschenkt.
[ 31 ] Was damit getan war, wird man, seinem vollen Umfange nach, nur ermessen, wenn man auf die Opposition blickt, mit der Haeckels umfassende Anwendung der darwinistischen Grundsätze von den Anhängern idealistischer Weltauffassungen aufgenommen worden sind. Man braucht dabei gar nicht auf diejenigen zu sehen, die sich in dem blinden Glauben an eine überlieferte Meinung gegen die «Affentheorie» wandten, oder auf diejenigen, die alle feinere, höhere Sittlichkeit gefährdet glauben, wenn die Menschen nicht mehr der Ansicht sind, daß sie einen «reineren, höheren Ursprung» haben. Man kann sich auch an solche halten, die durchaus geneigt sind, neue Wahrheiten in sich aufzunehmen. Aber auch solchen wurde es schwer, sich in diese neue Wahrheit zu finden. Sie fragten sich:
[ 32 ] Verleugnen wir nicht unser vernunftgemäßes Denken, wenn wir seinen Ursprung nicht mehr in einer allgemeinen Weltvernunft über uns, sondern in dem tierischen Reiche unter uns suchen? Solche Geister wiesen mit großem Eifer auf die Punkte hin, an denen die Haeckelsche Auffassung durch die Tatsachen noch im Stich gelassen zu werden schien. Und diese Geister haben mächtige Bundesgenossen in einer Anzahl von Naturforschern, die, aus einer merkwürdigen Befangenheit heraus, ihre Tatsachenkenntnis dazu benützen, fortwährend zu betonen, wo die Erfahrung noch nicht ausreiche, uni Haeckels Schlußfolgerungen zu ziehen. Der typische Repräsentant und zugleich der eindrucksvollste Vertreter dieses Naturforscherstandpunktes ist Rudolf Virchow. Man darf den Gegensatz Haeckels und Virchows etwa so charakterisieren: Haeckel vertraut auf die innere Konsequenz der Natur, von der Goethe meint, daß sie über die Inkonsequenz der Menschen hinwegtröste, und sagt sich: Wenn sich für gewisse, Fälle ein Naturprinzip als richtig ergeben hat und uns die Erfahrung fehlt, seine Richtigkeit in andern Fällen nachzuweisen, so ist kein Grund vorhanden, dem Fortgang unserer Erkenntnis Fesseln anzulegen; was uns heute noch die Erfahrung versagt, kann uns morgen gebracht werden. Virchow ist anderer Meinung. Er will ein umfassendes Prinzip so wenig wie möglich Boden gewinnen lassen. Er scheint zu glauben, daß man einem solchen Prinzip das Leben nicht sauer genug machen kann. Scharf spitzte sich der Gegensatz beider Geister auf der fünfzigsten Versammlung deutscher Naturforscher und Ärzte, im September 1877, zu. Haeckel hielt einen Vortrag über «Die heutige Entwickelung im Verhältnisse zur Gesamtwissenschaft.»
[ 33 ] Im Jahre 1894 fand sich Virchow genötigt, zu sagen: «Auf dem Wege der Spekulation ist man zu der Affentheorie gekommen; man hätte ebenso gut zu einer Elefanten- oder einer Schaftheorie kommen können.» Virchow fordert unumstößliche Beweise für diese Anschauung. Sobald aber etwas in die Erscheinung tritt, was sich als ein Glied in der Beweiskette ergibt, sucht Virchow seinen Wert auf jede mögliche Art zu entkräften.
[ 34 ] Ein solches Glied in der Beweiskette bilden die Knochenreste, die Eugen Dubois 1894 in Java gefunden hat. Sie bestehen aus einem Schädeldach, einem Oberschenkel und einigen Zähnen. Über diesen Fund entspann sich auf dem Leydener Zoologenkongreß eine interessante Diskussion. Von zwölf Zoologen waren drei der Meinung, daß die Knochenreste von einem Affen, drei, daß sie von einem Menschen stammen; sechs vertraten aber die Meinung, daß man es mit einer Übergangsform zwischen Mensch und Affen zu tun habe. Dubois hat in einleuchtender Weise gezeigt, in welchem Verhältnis das Wesen, dessen Reste man vor sich hatte, einerseits zu den gegenwärtigen Affen, anderseits zu den gegenwärtigen Menschen stehe. Die naturwissenschaftliche Entwickelungslehre muß solche Zwischenformen in besonderem Maße für sich in Anspruch nehmen. Sie füllen die Lücken aus, die zwischen den zahlreichen Formen der Organismen bestehen. Jede solche Zwischenform liefert einen neuen Beweis für die Verwandtschaft alles Lebendigen. Virchow widersetzte sich der Auffassung, daß die Knochenreste von einer solchen Zwischenform herrühren. Zunächst erklärte er, der Schädel stamme von einem Affen, der Oberschenkel von einem Menschen. Sachkundige Paläontologen sprachen sich aber nach dem gewissenhaften Fundberichte mit Entschiedenheit für die Zusammengehörigkeit der Reste aus. Virchow suchte seine Ansicht, daß der Oberschenkel nur von einem Menschen herrühren könne, durch die Behauptung zu stützen, eine Knochenwucherung an demselben beweise, daß an ihm eine Krankheit vorhanden gewesen sei, die nur durch sorgfältige menschliche Pflege geheilt worden sein könne. Dagegen sprach sich der Paläontologe Marsch dahin aus, daß ähnliche Knochenwucherungen auch bei wilden Affen vorkommen. Einer weiteren Behauptung Virchows, daß die tiefe Einschnürung zwischen dem Oberrand der Augenhöhlen und dem niederen Schädeldach des vermeintlichen Zwischenwesens für dessen Affennatur spreche, widersprach eine Bemerkung des Naturforschers Nehring, daß sich dieselbe Bildung an einem Menschenschädel von Santos in Brasilien finde. Diese Einwände Virchows kamen aus derselben Gesinnung, die ihn auch in den berühmten Schädeln von Neandertal, von Spy usw. krankhafte, abnorme Bildungen sehen läßt, während sie Haeckels Gesinnungsgenossen für Zwischenformen zwischen Affe und Mensch halten.
[ 35 ] Haeckel ließ sich durch keine Einwände das Vertrauen in seine Vorstellungsart rauben. Er behandelt unablässig die Wissenschaft von den gewonnenen Gesichtspunkten aus, und er wirkt durch populäre Darstellung seiner Naturauffassung auf das öffentliche Bewußtsein. In seiner «Systematischen Phylogenie, Entwurf eines natürlichen Systems der Organismen auf Grund der Stammesgeschichte» (1894-1896) suchte er die natürlichen Verwandtschaften der Organismen in streng wissenschaftlicher Weise darzustellen. In seiner «Natürlichen Schöpfungsgeschichte», die von 1868 bis 1908 elf Auflagen erlebt hat, gab er eine allgemeinverständliche Auseinandersetzung seiner Anschauungen. In seinen gemeinverständlichen Studien zur monistischen Philosophie «Welträtsel» lieferte er 1899 einen Überblick über seine naturphilosophischen Ideen, der rückhaltlos nach allen Seiten hin die Folgerungen seiner Grundgedanken darlegt. Zwischen allen diesen Arbeiten veröffentlichte er Studien über die mannigfaltigsten Spezialforschungen, überall den philosophischen Prinzipien und dem wissenschaftlichen Detailwissen in gleicher Weise in seiner Art Rechnung tragend.
[ 36 ] Das Licht, das von der monistischen Weltanschauung ausgeht, ist, nach Haeckels Überzeugung, dasjenige, das «die schweren Wolken der Unwissenheit und des Aberglaubens zerstreut, welche bisher undurchdringliches Dunkel über das wichtigste aller Erkenntnisprobleme verbreiteten, über die Frage nach dem Ursprung des Menschen, von seinem wahren Wesen und von seiner Stellung in der Natur». So hat er sich in der Rede ausgesprochen, die er am 26. August 1898 auf dem vierten internationalen Zoologenkongreß in Cambridge «Über unsere gegenwärtige Kenntnis vom Ursprung des Menschen» gehalten hat. Inwiefern seine Weltanschauung ein Band knüpft zwischen Religion und Wissenschaft, hat Haeckel auf eindringliche Weise dargelegt in seiner 1892 erschienenen Schrift «Der Monismus als Band zwischen Religion und Wissenschaft. Glaubensbekenntnis eines Naturforschers» .
[ 37 ] Wenn man Haeckel mit Hegel vergleicht, so ergibt sich in scharfen Zügen der Unterschied der Weltanschauungsinteressen in den beiden Hälften des neunzehnten Jahrhunderts. Hegel lebt ganz in der Idee und nimmt aus der naturwissenschaftlichen Tatsachenwelt nur so viel auf, als er zur Illustration seines idealen Weltbildes des braucht. Haeckel wurzelt mit allen Fasern seines Seins in der Tatsachenwelt und zieht aus dieser nur die Summe von Ideen, zu denen diese notwendig drängt. Hegel ist immer bestrebt, zu zeigen, wie alle Wesen darauf hinarbeiten, zuletzt im menschlichen Geiste den Gipfel ihres Werden s zu erreichen; Haeckel ist stets bemüht, zu erweisen, wie die kompliziertesten menschlichen Verrichtungen zurückweisen auf die einfachsten Ursprünge des Daseins. Hegel erklärt die Natur aus dem Geist; Haeckel leitet den Geist aus der Natur ab. Es darf deshalb von einer Umkehrung der Denkrichtung im Laufe des Jahrhunderts gesprochen werden. Innerhalb des deutschen Geisteslebens haben Strauß, Feuerbach und andere diese Umkehrung eingeleitet; in dem Materialismus hat die neue Richtung einen vorläufigen, extremen, in der Gedankenwelt Haeckels einen streng methodisch-wissenschaftlichen Ausdruck gefunden. Denn das ist das Bedeutsame bei Haeckel, daß seine ganze Forschertätigkeit von einem philosophischen Geiste durchdrungen ist. Er arbeitet durchaus nicht nach Resultaten hin, die aus irgendwelchen Motiven als Ziele der Weltanschauung oder des philosophischen Denkens aufgestellt sind; aber sein Verfahren ist philosophisch. Die Wissenschaft tritt bei ihm unmittelbar mit dem Charakter der Weltanschauung auf. Die ganze Art seines Anschauens der Dinge hat ihn zum Bekenner des entschiedensten Monismus bestimmt. Er sieht Geist und Natur mit gleicher Liebe an. Deshalb konnte er den Geist in den einfachsten Lebewesen noch finden. Ja, er geht noch weiter. Er forscht nach den Spuren des Geistes in den unorganischen Massenteilchen. «Jedes Atom» - sagt er - «besitzt eine inhärente Summe von Kraft und ist in diesem Sinne beseelt. Ohne die Annahme einer Atomseele sind die gewöhnlichsten und die allgemeinsten Erscheinungen der Chemie unerklärlich. Lust und Unlust, Begierde und Abneigung, Anziehung und Abstoßung müssen allen Massenatomen gemeinsam sein; denn die Bewegungen der Atome, die bei Bildung und Auflösung einer jeden chemischen Verbindung stattfinden müssen, sind nur erklärbar, wenn wir ihnen Empfindung und Willen beilegen, und nur hierauf allein beruht im Grunde die allgemein angenommene chemische Lehre von der Wahlverwandtschaft.» Und wie er den Geist bis ins Atom hinein verfolgt, so das rein materiell-mechanische Geschehen bis in die erhabensten Geistesleistungen herauf. «Geist und Seele des Menschen sind auch nichts anderes, als Kräfte, die an das materielle Substrat unseres Körpers untrennbar gebunden sind. Wie die Bewegungskraft unseres Fleisches an die Formelemente der Muskeln, so ist die Denkkraft unseres Geistes an die Formelemente des Gehirns gebunden. Unsere Geisteskräfte sind eben Funktionen dieser Körperteile, wie jede Kraft die Funktion eines materiellen Körpers ist.»
[ 38 ] Man darf aber diese Vorstellungsweise nicht verwechseln mit derjenigen, die in unklar-mystischer Art in die Naturwesen Seelen hineinträumt und diese der menschlichen mehr oder weniger ähnlich sein läßt. Haeckel ist ein scharfer Gegner der Weltanschauung, die Eigenschaften und Tätigkeiten des Menschen in die Außenwelt verlegt. Seine Verurteilung der Vermenschlichung der Natur, des Anthropomorphismus, hat er wiederholt mit nicht mißzuverstehender Deutlichkeit ausgesprochen. Wenn er der unorganischen Masse oder den einfachsten Organismen eine Beseeltheit zuschreibt, so meint er damit nichts weiter, als die Summe der Kraftäußerungen, die wir an ihnen beobachten. Er hält sich streng an die Tatsachen. Empfindung und Wille des Atoms sind ihm keine mystischen Seelenkräfte, sondern sie erschöpfen sich in dem, was wir als Anziehung und Abstoßung wahrnehmen. Er will nicht sagen: Anziehung und Abstoßung sind eigentlich Empfindung und Wille, sondern Anziehung und Abstoßung sind auf niedrigster Stufe das, was Empfindung und Wille auf höherer Stufe sind. Die Entwickelung ist ja nicht ein bloßes Herausentwickeln der höheren Stufen des Geistigen aus dem Niedrigen, in denen sie schon verborgen liegen, sondern ein wirkliches Aufsteigen zu neuen Bildungen (vgl. oben S. 403 ff.), eine Steigerung von Anziehung un4 Abstoßung zu Empfindung und Wille. Diese Grundanschauung Haeckels stimmt in gewissem Sinne mit der Goethes überein, der sich darüber mit den Worten ausspricht: Die Erfüllung seiner Naturanschauung sei ihm durch die Erkenntnis der «zwei großen Triebräder aller Natur» geworden, der Polarität und der Steigerung, jene «der Materie, insofern wir sie materiell, diese ihr dagegen, insofern wir sie geistig denken, angehörig; jene ist in immerwährendem Anziehen und Abstoßen, diese in immerwährendem Aufsteigen. Weil aber die Materie nie ohne Geist, der Geist nie ohne Materie existiert und wirksam sein kann, so vermag auch die Materie sich zu steigern, so wie sich's der Geist nicht nehmen läßt anzuziehen und abzustoßen.»
[ 39 ] Der Bekenner einer solchen Weltanschauung läßt sich daran genügen, die tatsächlich in der Welt vorhandenen Dinge und Vorgänge auseinander abzuleiten. Die idealistischen Weltanschauungen bedürfen zu der Ableitung eines Dinges oder Vorganges Wesenheiten, die nicht innerhalb des Bereiches des Tatsächlichen gefunden werden. Haeckel leitet die Form des Becherkeimes, die im Laufe der tierischen Entwickelung auftritt, aus einem tatsächlich einmal vorhandenen Organismus ab. Ein Idealist sucht nach ideellen Kräften, unter deren Einfluß der sich entwickelnde Keim zur Gastrula wird. Der Monismus Haeckels zieht alles, was er zur Erklärung der wirklichen Welt braucht, auch aus dieser wirklichen Welt heraus. Er hält im Reiche des Wirklichen Umschau, um zu erkennen, wie die Dinge und Vorgänge einander erklären. Seine Theorien sind ihm nicht wie die des Idealisten dazu da, zu dem Tatsächlichen ein Höheres zu suchen, einen ideellen Inhalt, der das Wirkliche erklärt, sondern dazu, daß sie ihm den Zusammenhang des Tatsächlichen selbst begreiflich machen. Fichte, der Idealist, hat nach der Bestimmung des Menschen gefragt. Er meinte damit etwas, was sich nicht in den Formen des Wirklichen, des Tatsächlichen erschöpft; er meinte etwas, was die Vernunft zu dem tatsächlich gegebenen Dasein hinzufindet; etwas, was mit einem höheren Lichte die reale Existenz des Menschen durchleuchtet. Haeckel, der monistische Weltbetrachter, fragt nach dem Ursprunge des Menschen, und er meint damit den realen Ursprung, die niederen Wesenheiten, aus denen sich der Mensch durch tatsächliche Vorgänge entwickelt hat.
[ 40 ] Es ist bezeichnend, wie Haeckel die Beseelung der niederen Lebewesen begründet. Ein Idealist würde sich dabei auf Vernunftschlüsse berufen. Er würde mit Denknotwendigkeiten kommen. Haeckel beruft sich darauf, was er gesehen hat. «Jeder Naturforscher, der gleich mir lange Jahre hindurch die Lebenstätigkeit der einzelligen Protisten beobachtet hat, ist positiv überzeugt, daß auch sie eine Seele besitzen; auch diese Zellseele besteht aus einer Summe von Empfindungen, Vorstellungen und Willenstätigkeiten; das Empfinden, Denken und Wollen unserer menschlichen Seelen ist nur stufenweise davon verschieden.» Der Idealist spricht der Materie den Geist zu, weil er sich nicht denken kann, daß aus geistloser Materie Geist entstehen kann. Er glaubt, man müsse den Geist leugnen, wenn man ihn nicht da sein läßt, bevor er da ist, das heißt in all den Daseinsformen, wo noch kein Organ, kein Gehirn für ihn da ist. Für den Monisten gibt es einen solchen Ideengang gar nicht. Er spricht nicht von einem Dasein, das sich als solches nicht auch äußerlich darstellt. Er teilt nicht den Dingen zweierlei Eigenschaften zu: solche, die an ihnen wirklich sind, und sich an ihnen äußern, und solche, die insgeheim in ihnen sind, um sich erst auf einer höheren Stufe, zu der sich die Dinge entwickeln, zu äußern. Für ihn ist da, was er beobachtet, weiter nichts. Und wenn sich das Beobachtete weiter entwickelt, und sich im Laufe seiner Entwickelung steigert, so sind die späteren Formen erst in dem Augenblicke vorhanden, in dem sie sich wirklich zeigen.
[ 41 ] Wie leicht der Haeckelsche Monismus nach dieser Richtung hin mißverstanden werden kann, das zeigen die Einwände, die der geistvolle Bartholomäus von Carneri gemacht hat, der auf der andern Seite für den Aufbau einer Ethik dieser Weltanschauung Unvergängliches geleistet hat. In seiner Schrift «Empfindung und Bewußtsein. Monistische Bedenken» (1893) meint er, der Satz: «Kein Geist ohne Materie, aber auch keine Materie ohne Geist» würde uns berechtigen, die Frage auf die Pflanze, ja auf den nächsten besten Felsblock auszudehnen, und auch diesen Geist zuzuschreiben. Es sei aber doch zweifellos, daß dadurch eine Verwirrung geschaffen werde. Es sei doch nicht zu übersehen, daß nur durch die Tätigkeit der Zellen der grauen Hirnrinde Bewußtsein entstehe. «Die Überzeugung, daß es keinen Geist ohne Materie gehe, daß heißt, daß alle geistige Tätigkeit an eine materielle Tätigkeit gebunden sei, mit deren Ende auch sie ihr Ende erreicht, fußt auf Erfahrung, während nichts in der Erfahrung dafür spricht, daß mit der Materie überhaupt Geist verbunden sei.» Wer die Materie, die keinen Geist verrät, beseele, gliche dem, der nicht dem Mechanismus der Uhr, sondern schon dem Metalle, aus dem sie verfertigt ist, die Fähigkeit zuschriebe, Zeitangaben zu machen.
[ 42 ] Haeckels Auffassung wird, richtig verstanden, von den Bedenken Carneris nicht getroffen. Davor wird sie dadurch geschützt, daß sie sich streng an die Beobachtung hält. In seinen «Welträtseln» sagt Haeckel: «Ich selbst habe die Hypothese des Atombewußtseins niemals vertreten Ich habe vielmehr ausdrücklich betont, daß ich mir die elementaren psychischen Tätigkeiten der Empfindung und des Willens, die man den Atomen zuschreiben kann, unbewußt vorstelle.» Was Haeckel will, ist nichts anderes, als daß man in der Erklärung der Naturerscheinungen keinen Sprung eintreten lasse, daß man die komplizierte Art, wie durch das Gehirn Geist erscheint, zurückverfolge bis zu der einfachsten Art, wie die Masse sich anzieht und abstößt. Haeckel sieht als eine der wichtigsten Erkenntnisse der modernen Wissenschaft die Entdeckung der Denkorgane durch Paul Flechsig an. Dieser hat betont, daß in der grauen Rindenzone des Hirnmantels vier Gebiete für die zentralen Sinnesorgane liegen, vier «innere Empfindungssphären» , die Körperfühlsphäre, die Riechsphare, die Sehsphäre und die Hörsphäre. Zwischen diesen vier Sinnesherden liegen die Denkherde, die «realen Organe des Geisteslebens»; sie «sind die höchsten Werkzeuge der Seelentätigkeit, welche das Denken und das Bewußtsein vermitteln ... Diese vier Denkherde, durch eigentümliche und höchst verwickelte Nervenstruktur von den zwischenliegenden Sinnesherden ausgezeichnet, sind die wahren Denkorgane, die einzigen Organe unseres Bewußtseins. In neuester Zeit hat Flechsig nachgewiesen, daß in einem Teile derselben sich beim Menschen noch ganz besonders verwickelte Strukturen finden, welche den übrigen Säugetieren fehlen, welche die Überlegenheit des menschlichen Bewußtseins erklären.» (Welträtsel, 5. 212 f.)
[ 43 ] Solche Ausführungen zeigen deutlich genug, daß es Haeckel nicht wie den idealistischen Welterklärern darauf ankommt, in die niederen Stufen des materiellen Daseins den Geist schon hineinzulegen, um ihn auf den höheren wiederzufinden, sondern darauf, an der Hand der Beobachtung die einfachen Erscheinungen bis zu den komplizierten zu verfolgen, um zu zeigen, wie die Tätigkeit der Materie, die sich auf primitivem Gebiete als Anziehung und Abstoßung äußert, sich zu den höheren geistigen Verrichtungen steigert.
[ 44 ] Haeckel sucht nicht ein allgemeines geistiges Prinzip, weil er mit der allgemeinen Gesetzmäßigkeit der Natur- und Geisteserscheinungen nicht ausreicht, sondern er reicht für sein Bedürfnis völlig mit dieser allgemeinen Gesetzmäßigkeit aus. Die Gesetzmäßigkeit, die sich in den geistigen Verrichtungen ausspricht, ist ihm von gleicher Art mit derjenigen, die im Anziehen und Abstoßen der Massenteilchen zum Vorschein kommt. Wenn er die Atome beseelt nennt, so hat das eine ganz andere Bedeutung, als wenn dies ein Bekenner einer idealistischen Weltanschauung tut. Der letztere geht vom Geiste aus, und nimmt die Vorstellungen, die er an der Betrachtung des Geistes gewonnen hat, mit hinunter in die einfachen Verrichtungen der Atome, wenn er diese beseelt denkt. Er erklärt also die Naturerscheinungen aus den Wesenheiten, die er erst selbst in sie hineingelegt hat. Haeckel geht von der Betrachtung der einfachsten Naturerscheinungen aus und verfolgt diese bis in die geistigen Verrichtungen herauf. Er erklärt also die Geisteserscheinungen aus Gesetzen, die er an den einfachsten Naturerscheinungen beobachtet hat.
[ 45 ] Haeckels Weltbild kann in einer Seele entstehen, deren Beobachtung sich nur auf Naturvorgänge und Naturwesen erstreckt. Eine solche Seele wird den Zusammenhang innerhalb dieser Vorgänge und Wesen verstehen wollen. Ihr Ideal kann werden, zu durchschauen, was die Vorgänge und Wesenheiten über ihr Werden und Zusammenwirken selbst sagen und alles streng abzulehnen, was zu einer Erklärung des Geschehens und Wirkens von außen hinzugedacht wird. Ein solches Ideal verfährt mit der ganzen Natur so, wie man etwa bei Erklärung des Mechanismus einer Uhr verfährt. Man braucht nichts zu wissen über den Uhrmacher, über dessen Geschicklichkeiten und über die Gedanken, welche er sich bei dem Verfertigen der Uhr gemacht hat. Man versteht den Gang der Uhr, wenn man die mechanischen Gesetze des Zusammenwirkens der Teile durchschauen kann. Innerhalb gewisser Grenzen hat man mit einem solchen Durchschauen alles getan, was zur Erklärung des Ganges der Uhr zulässig ist. Ja, man muß sich klar darüber sein, daß die Uhr selbst - als solche - nicht erklärt werden kann, wenn man eine andere Erklärungsweise zuläßt. Wenn man zum Beispiel außer den mechanischen Kräften und Gesetzen noch besondere geistige Kräfte ersinnen würde, welche die Zeiger der Uhr in Gemäßheit des Ganges der Sonne vorwärts rückten. Als solche zu den Naturvorgängen hinzuersonnene Kräfte erscheint Haeckel alles, was einer besonderen Lebenskraft ähnlich ist, oder eine Macht, die auf eine «Zweckmäßigkeit» in den Wesen hinarbeitet. Er will über die Naturvorgänge nichts anderes denken, als was diese selbst für die Beobachtung aussprechen. Sein Gedankengebäude soll das der Natur abgelauschte sein. Für die Betrachtung der Weltanschauungsentwickelung stellt sich dieses Gedankengebäude gewissermaßen als Gegengabe von seiten der Naturwissenschaft an die Hegelsche Weltanschauung dar, die in ihrem Gedankengemälde nichts aus der Natur, sondern alles aus der Seele geschöpft haben will. Wenn Hegels Weltanschauung sagte: Das selbstbewußte Ich findet sich, indem es das reine Gedankenerlebnis in sich hat, - so könnte die Haeckelsche Naturanschauung erwidern: Dieses Gedankenerlebnis ist ein Ergebnis der Naturvorgänge, ist deren höchstes Erzeugnis. Und wenn sich die Hegelsche Weltanschauung von solcher Erwiderung nicht befriedigt fühlte, so könnte die Haeckelsche Naturanschauung fordern: Zeige mir solche innere Gedankenerlebnisse, die nicht wie ein Spiegel dessen erscheinen, was außer den Gedanken geschieht. Darauf müßte eine Philosophie zeigen, wie der Gedanke in der Seele lebendig werden und wirklich eine Welt zeugen kann, die nicht bloß der gedankliche Widerschein der Außenwelt ist. Der Gedanke, der bloß gedacht ist, kann der Haeckelschen Naturanschauung nichts entgegenstellen. Diese kann zum Vergleich behaupten: Man kann doch auch in der Uhr nichts finden, was auf die Person usw. des Uhrmachers schließen läßt. Haeckels Naturanschauung ist auf dem Wege, zu zeigen, wie man, solange man bloß der Natur gegenübersteht, über diese nichts aussagen kann, als was diese selbst aussagt. Insofern tritt diese Naturanschauung in dem Gange der Weltanschauungsentwickelung bedeutsam auf. Sie beweist, daß Philosophie sich ein Feld schaffen muß, das, über die an der Natur gewonnenen Gedanken hinaus, in dem selbstschöpferischen Gebiete des Gedankenlebens liegt. Sie muß den in einem vorigen Abschnitt angedeuteten über Hegel hinausgehenden Schritt machen. Sie kann nicht bestehen in einem bloßen Verfahren, das auf demselben Felde stehenbleibt, auf dem die Naturwissenschaft steht. Haeckel hat wohl nicht das mindeste Bedürfnis, auf einen solchen Schritt der Philosophie auch nur im geringsten die Aufmerksamkeit zu wenden. Seine Weltanschauung läßt die Gedanken in der Seele lebendig werden, doch dies nur insoweit, als deren Leben durch die Beobachtung der Naturvorgänge angeregt ist. Was der Gedanke als Weltbild schaffen kann, wenn er ohne diese Anregung in der Seele lebendig wird, das müßte nun eine höhere Weltanschauung zu dem Haeckelschen Naturbilde hinzufügen. Man muß ja auch über dasjenige hinausgehen, was die Uhr selbst sagt, wenn man zum Beispiel die Gesichtsform des Uhrmachers kennenlernen will. Man hat deshalb kein Recht, zu behaupten, daß die Haekkelsche Naturanschauung über die Natur selbst anders sprechen sollte, als Haeckel da spricht, wo er vorbringt, was er positiv über Naturvorgänge und Naturwesen beobachtet hat.
Darwinism and worldview
[ 1 ] If the idea of expediency were to undergo a reform in the sense of a natural world view, the expedient formations of living nature would have to be explained in the same way as physicists and chemists explain inanimate processes. When a magnetic bar attracts iron filings to itself, no physicist thinks of a force working in the bar towards the goal, the purpose of the attraction. When hydrogen and oxygen combine to form water, the chemist does not interpret it as if there were something at work in the two substances that had the purpose of forming water in mind. An explanation of living beings governed by just such a natural sense must say: organisms become purposeful without anything in nature aiming at this purposefulness. Purposefulness arises without being predisposed as such anywhere. Charles Darwin gave such an explanation of purposefulness. He took the standpoint of recognizing that nothing in nature wants what is purposeful. Nature does not even consider whether what arises in it is purposeful or not. It therefore produces the inexpedient and the expedient indiscriminately.
[ 2 ] What is purposeful at all? But that which is so arranged that the external conditions of existence correspond to its needs, its living conditions. What is inexpedient, on the other hand, is that which is not. What will happen if, in the complete purposelessness of nature, all degrees of the more or less purposive arise from the most purposive to the least purposive? Every being will seek to shape its existence in accordance with the given conditions. The expedient succeeds in this without further ado, the more or less expedient only to a small degree. Now there is an additional factor: nature is not a frugal host with regard to the production of living beings. The number of germs is immense. This superabundance in the production of germs is only matched by a limited measure of the means of life. The result will be that those beings will have an easier time in their development which are more suitably formed for the appropriation of food. If a more purposeful being strives for the preservation of its existence alongside a less purposeful being, the more purposeful will outstrip the less purposeful. The latter must perish alongside the former. The efficient, i.e. the expedient, preserves itself, the inefficient, i.e. the inexpedient, does not. This is the "struggle for existence". It causes the expedient to survive, even if in nature the inexpedient arises indiscriminately alongside the expedient. Through a law that is so objective, so devoid of wisdom, as only a mathematical or mechanical law of nature can be, the course of natural development receives the tendency towards expediency, without this tendency being somehow inherent in nature.
[ 3 ] Darwin was led to this idea by the work of the national economist Malthus "On the Conditions and Consequences of the Increase of Population". In this work it is stated that an incessant competition takes place within human society because the population grows much faster than the amount of food. Darwin generalized this law established here for human history into a comprehensive law for the entire living world.
[ 4 ] Darwin now wanted to show how this struggle for existence becomes the creator of the manifold forms of living beings, how it overturns the old Linnaean principle that we "count as many species in the animal and plant kingdoms as there are different forms created in principle". Darwin's doubts about this principle became clear when he was on a trip to South America and Australia in the summer of 1831. He explains how these doubts took root in his mind: "When, during the voyage of the Beagle, I visited the Galapagos Archipelago, which lies in the Pacific Ocean about five hundred English miles from the South American coast, I found myself surrounded by peculiar species of birds, reptiles and snakes, which exist nowhere else in the world. But almost all of them had an American flavor. In the song of the mocking-bird, in the sharp cry of the vulture, in the large, lantern-like opuntia, I clearly perceived the proximity of America; and yet these islands were so many miles distant from the mainland, and differed widely from it in their geological constitution and climate. Even more surprising was the fact that most of the inhabitants of each island in this small archipelago were specifically different, though closely related to each other. I often wondered at the time how these peculiar animals and people had evolved. The simplest way seemed to be that the inhabitants of the various islands were descended from one another and had undergone modifications in the course of their descent, and that all the inhabitants of the archipelago were descended from those of the nearest mainland, namely America, from which colonization would naturally have originated. But for a long time it remained an inexplicable problem to me how the necessary degree of modification could have been achieved." The answer to this how lies in the natural conception of the development of the living. Just as the physicist places a substance in different ratios in order to get to know its properties, Darwin observed the phenomena that arise in living beings in different ratios after his return home. He carried out breeding experiments with pigeons, chickens, dogs, rabbits and cultivated plants. They showed how living forms continually change in the course of their reproduction. In certain circumstances, certain living beings change after a few generations in such a way that, if one compares the newly created forms with their ancestors, one could speak of two completely different species, each of which follows its own organizational plan. The breeder uses such variability of forms to develop cultivated organisms that correspond to certain intentions. He can breed a type of sheep with particularly fine wool if he only allows those individuals in his flock to reproduce that have the finest wool. Within the offspring, he again selects the individuals with the finest wool. The fineness of the wool then increases over the generations. After some time, a sheep species is obtained that is very far removed from its ancestors in terms of wool formation. The same is the case with other characteristics of living beings. Two things follow from this fact. First, that there is a tendency in nature to change living beings; and second, that a quality which has begun to change in a certain direction will increase in that direction if, in the reproduction of living beings, those individuals are kept away which do not yet possess this quality. The organic forms thus take on other characteristics in the course of time and remain in the direction of their transformation once it has begun. They transform and pass on transformed characteristics to their descendants.
[ 5 ] The natural conclusion from this observation is that transformation and inheritance are two driving principles in the development of living beings. If one now assumes that in a natural way in the world the beings change in such a way that the purposeful arises alongside the inexpedient and the more or less purposeful, then one must also presuppose a struggle of the manifold changed forms. This struggle brings about haphazardly what the breeder does systematically. Just as he excludes from reproduction those individuals who would bring into the development what he does not want, so the struggle for existence eliminates the inexpedient. Only what is expedient for development remains. Thus, like a mechanical law, the tendency to constant perfection is laid into it. Darwin, having recognized this and thus laid a firm foundation for the natural world view, was able to place the enthusiastic words at the end of his work "The Origin of Species", which ushered in a new epoch of thought: "From the struggle of nature, from hunger and death, therefore, the highest thing we are able to conceive is the production of the higher animals. There is something magnificent in this view of life, according to which it was originally created by the Creator with all its various powers from few forms, or perhaps only one; and that, while this planet moves in circles according to the definite laws of gravitation, from a simple beginning an endless number of the most beautiful and wonderful forms have been and are still being developed." At the same time it can be seen from this sentence that Darwin did not arrive at his view through any anti-religious sentiments, but solely from the conclusions that arose for him from the clearly speaking facts. It was certainly not the case with him that hostility to the needs of feeling determined him to a reasonable view of nature, for he tells us clearly in his book how the world of ideas he had gained spoke to his heart: "Very eminent writers seem to be entirely satisfied with the view that each of the species was created independently. In my opinion, it is more consistent with the laws impressed on matter by the Creator, so far as we know, that the generation and extinction of the past and present inhabitants of the earth, as well as the determinations of the birth and death of an individual, are dependent on secondary causes. If I regard all beings not as special creations, but as linear descendants of a few beings who lived long before the younger geological strata were deposited, they seem to me to be ennobled by this ... We can look forward with confidence to a future of great length. And since natural selection only works through and for the good of each being, all physical and mental talents will strive towards perfection."
[ 6 ] In a wealth of facts, Darwin showed how organisms grow and reproduce, how in the course of their further development they inherit characteristics once adopted, how new organs arise and change through use or disuse, how creatures adapt to their conditions of existence; and finally how the struggle for existence makes a natural selection (breeding selection), whereby diverse, ever more perfect forms arise.
[ 7 ] This seems to provide an explanation of purposeful beings that does not make it necessary to proceed differently in organic nature than in inorganic nature As long as such an explanation could not be given, one had to admit, if one wanted to be consistent, that wherever a purposeful being arises within nature, a power foreign to nature intervenes. This basically admitted a miracle for every such case.
[ 8 ] Those who, for decades before the publication of Darwin's work, had been striving for a natural view of the world and life, now felt in the most vivid way that a new direction of thought had been given. Such a feeling was expressed in 1872 by David Friedrich Strauß in his "Old and New Faith" with the words: "One sees that ... it must go where the flags flutter merrily in the wind. Yes, merry, in the sense of the purest, most sublime joy of the spirit. We philosophers and critical theologians had good reason when we decreed the miracle to be a thing of the past; our powerlessness died away without effect, because we did not know how to make it dispensable, did not know how to prove a force of nature that could replace it in those places where it had hitherto been considered most indispensable. Darwin has proved this natural force, this natural process; he has opened the door through which a happier posterity will throw out the miracle for ever. Everyone who knows what depends on wonder will praise him as one of the greatest benefactors of the human race."
[ 9 ] Through Darwin's idea of expediency, it is possible to really think of the concept of development in terms of natural law. The old theory of nesting, which assumes that everything that comes into being was already there in a hidden form (cf. page 286 of the first volume of this book), was thus robbed of its last hopes. Within a developmental process conceived in Darwin's sense, the perfect is in no way already contained in the imperfect. For the perfection of a higher being arises through processes that have absolutely nothing to do with the ancestors of this being. Consider: a certain developmental series has reached the marsupials. There is nothing, absolutely nothing, of a higher, more perfect form in the form of the marsupials. It contains only the ability to transform itself indiscriminately in the further course of its reproduction. Conditions now arise which are independent of any "inner" developmental system of the marsupial form, but which are such that, of all possible forms of transformation, the marsupials develop into the prosimians. The marsupial form did not contain the semi-ape form any more than the direction of a rolling billiard ball contains the path it takes after it has been pushed by a second ball.
[ 10 ] Those who were accustomed to an idealistic way of thinking did not find it easy to understand this reformed concept of development. The extremely perceptive and subtle mind of Friedrich Theodor Vischer, who emerged from Hegel's school, wrote in an essay as late as 1874: "Development is an unwinding from a germ, which progresses from trial to trial until the image that lay in the germ as a possibility has become real, but then, standing still, holds on to the form found as a permanent one. In fact, every concept begins to waver when we consider the types that have existed on our planet for so many millennia and, above all, when we consider our own human type to still be changeable. We can then follow our thoughts, indeed our laws of thought, our feelings, the ideal images of our imagination, which are nothing more than purifying reproductions of forms of the ones we know
[ 11 ] Nature: we can no longer trust any of these firm supports of our soul. Everything is called into question." And at another point in the same essay we read: "For example, it is still somewhat difficult for me to believe that one gets the eye from seeing, the ear from hearing. The immense weight that is placed on the choice of breed also does not make sense to me."
[ 12 ] If Vischer had been asked whether he imagined that in hydrogen and oxygen there was an image of water in embryo, so that it could develop out of them, he would undoubtedly have answered: No; neither in oxygen nor in hydrogen is there anything of water; the conditions for the formation of this substance are only present at the moment when hydrogen and oxygen come together under certain conditions. Does it need to be different if the interaction of the marsupials with the external conditions of existence gives rise to the prosimians? Why should the semi-apes already lie hidden in the marsupials as a possibility, as an image, so that they can develop out of them? What arises through development arises anew without having been present in any form beforehand.
[ 13 ] Prudent naturalists felt the weight of the new theory of purpose no less than thinkers like Strauss. Without doubt, Hermann Helmholtz was one of those who could be considered representatives of such level-headed natural scientists in the fifties and sixties. He emphasized how the wonderful and ever more richly unfolding purposefulness in the structure and actions of living beings in the face of growing science virtually challenged us to compare the processes of life with human actions. For these are the only series of phenomena that have a character similar to that of organic phenomena. Indeed, the purposeful arrangements in the world of organisms usually far exceed what human intelligence is capable of creating. It is therefore not surprising that the construction and activity of the living world has been attributed to human intelligence. "Before Darwin," says Helmholtz, "one therefore had to admit only two explanations of organic purposefulness, both of which, however, attributed it to the intervention of free intelligence in the course of natural phenomena. Either, in accordance with the vitalistic theory, the processes of life were regarded as continuously guided by a life-soul; or, for each living species, one resorted to an act of supernatural intelligence through which it was supposed to have come into being ... Darwin's theory contains an essentially new creative idea. It shows how a purposefulness of formation in organisms can arise through the blind operation of a natural law, even without any interference from intelligence. This is the law of the transmission of individual peculiarities from parents to offspring; a law that had long been known and recognized and only needed a certain delimitation." Helmholtz is now of the opinion that the principle of natural selection in the struggle for existence has provided such a delimitation of the law.
[ 14 ] And a researcher who was no less cautious than Helmholtz, J. Henle, stated in a lecture: "If the experiences of artificial breeding were to be applied to the Oken-Lamarck hypothesis, it would have to be shown how nature begins in order to take the steps by which the experimenter achieves his goal. This is the task which Darwin set himself and pursued with admirable zeal and ingenuity."
[ 15 ] The materialists were the most enthusiastic of all about Darwin's work. It had long been clear to them that sooner or later such a man would have to come along to shed philosophical light on the accumulated facts that were pressing for a guiding thought. In their opinion, after Darwin's discovery, the world view for which they had campaigned could not fail to triumph.
[ 16 ] Darwin approached his task as a natural scientist. He initially kept within the boundaries of such a scientist. The fact that his thoughts could shed light on the fundamental questions of worldview, on the relationship of man to nature, is only touched on in his fundamental book: "In the future I see an open field for far more important research. Psychology will certainly rely on ... the foundation: the necessity of acquiring every mental power and ability step by step. Much light may yet be shed on the origin of man and his history." According to Büchner, this question about the origin of man became a matter close to the materialists' hearts. In the lectures he gave in Offenbach in the winter of 1866/67, he said: "Must the theory of transformation also be applied to our own race, to man or to ourselves? Must we accept that the same principles or rules which have brought other organisms into being should also apply to our own origin and origin? Or do we - the masters of creation - make an exception?"
[ 17 ] Natural science clearly taught that humans could not make an exception. On the basis of precise anatomical studies, the English naturalist Huxley was able to state in 1863 in his "Testimonies to the Position of Man in Nature": "The critical comparison of all the organs and their modifications within the ape series leads us to this one and the same result, that the anatomical differences which separate man from the gorilla and chimpanzee are not so great as the differences which separate these apes from the lower species of monkeys." Faced with such facts, could one still doubt that natural development, which through growth and reproduction, heredity, variability of forms and the struggle for existence has brought about the series of organic beings up to the ape, has ultimately also produced man in exactly the same way?
[ 18 ] In the course of the century, the basic view penetrated ever deeper into the body of scientific knowledge, which Goethe was imbued with - albeit in his own way - and because of which he set about with all his energy to correct the opinion of his contemporaries that man lacked a so-called intermaxillary bone in the upper jaw. All animals should have this bone, but not humans, they thought. And this was seen as proof that man was anatomically different from animals, that he was conceived differently according to his blueprint. Goethe's natural way of thinking required him to carry out diligent anatomical studies to dispel this error. And when he had succeeded in his goal, he wrote to Herder, full of the feeling that he had done something that was highly conducive to the knowledge of nature: "I compared ... human and animal skulls, got to the bottom of it, and lo, there it is! Now I beg you, let nothing be known to you, for it must be kept secret. It should also make you very happy; for it is like the keystone to man, it is not missing, it is also there! But how!"
[ 19 ] Under the influence of such ideas, the great worldview question of man's relationship to himself and to the outside world became the task of showing by scientific means what the actual processes are that have led to the formation of man in the course of development. This changed the point of view from which one sought to explain natural phenomena. As long as one saw in every organism, and thus also in man, a purposeful construction plan realized, one had to take this purpose into consideration when explaining the beings. One had to take into account the fact that in the embryo the later organism announces itself in advance. Extended to the whole universe, this meant that the explanation of nature best fulfilled its task by showing how nature, at the earlier stages of its development, prepares itself to produce the later ones and, at the summit, man.
[ 20 ] The modern idea of development rejected all tendency of knowledge to see the later in the earlier. For them, the later was in no way contained in the earlier. On the other hand, it increasingly developed the principle of seeking the earlier in the later. This principle was an integral part of the principle of inheritance. One can almost speak of a reversal of the direction of the need for explanation. This reversal became important for the formation of ideas about the development of the individual organic organism from the egg to the mature state, for the so-called germ history (ontogeny). Instead of holding it against themselves that the later organs are prepared in the embryo, they began to compare the forms that the organism assumes in the course of its individual development from the egg to maturity with other forms of organisms. Lorenz Oken was already following such a trail. In the fourth volume of his "Allgemeine Naturgeschichte für alle Stände" (p. 468), he wrote: "Through my physiological investigations, I came to the conclusion a number of years ago that the developmental states of the chick in the egg are similar to the various classes of animals, so that at first it possesses, as it were, only the organs of the infusoria, then gradually acquires those of the polyps, jellyfish, mussels, snails, etc.. Conversely, I then had to regard the animal classes as stages of development which paralleled those of the shell. This view of nature demanded the most exact comparison of those organs which in each higher animal class are newly added to the others, and also of those which develop successively in the calyx during breeding. A perfect parallelism is of course not so easy to establish in a subject so difficult and so far from being sufficiently observed. But to prove that it really exists is indeed not difficult: this is shown most clearly by the metamorphosis of insects, which is nothing more than a development of the young that takes place outside the egg before our eyes, and so slowly that we can observe and examine each embryonic state with leisure." Oken compares the metamorphoses of insects with other animals and finds that the caterpillars bear the greatest resemblance to worms, the pupae to crabs. From such similarities, the ingenious thinker concludes: "There is therefore no doubt that there is a striking similarity here, which justifies the idea that the history of development in the egg is nothing other than a repetition of the history of the creation of the animal classes." It was in the nature of this witty man to suspect a great idea on the basis of a lucky aperçu. He did not even need the correspondingly correct facts for such a hunch. However, it is also in the nature of such intuited ideas that they do not make a great impression on the workers in the field of science. Oken flashes like a comet in the German worldview sky. He develops a wealth of light. From a rich store of ideas, he provides guiding concepts for the most diverse areas of fact. However, the way in which he established factual contexts usually had something violent about it. He worked towards the punch line. This was also the case with the above-mentioned law of the repetition of certain animal forms in the germ development of others.
[ 21 ] In contrast to Oken, Carl Ernst von Baer stuck to the purely factual as far as possible when he spoke of what led Oken to his idea in his "Developmental History of Animals" in 1828. "The embryos of mammals, birds, lizards and snakes, and probably also of tortoises, are in their early states uncommonly similar to each other both as a whole and in the development of the individual parts; so similar that the embryos can often only be distinguished by their size. I possess two small embryos in wine spirit, for which I have neglected to note the names; and I am now quite unable to determine the class to which they belong. They may be lizards, small birds or very young mammals. The head and trunk are so similar in these animals. However, the extremities are still missing in these embryos. Even if they were there, at the first stage of formation, they would teach us nothing, since the feet of lizards and mammals, the wings and feet of birds, and the hands and feet of humans develop from the same basic form." Such facts of germ history were bound to arouse the greatest interest among those thinkers who were inclined to Darwinism with their convictions. Darwin had proved the possibility that organic forms change, and that by way of transformation the species living today descend from a few, perhaps only from one original one. Now the manifold living beings show themselves to be so similar in their first stages of development that they can hardly or not at all be distinguished. In 1864, Fritz Müller made an organic connection between this fact of similarity and the idea of descent in his thoughtful essay "For Darwin". Müller is one of those high-minded personalities whose souls absolutely need a natural world view to breathe spiritually. He also felt satisfaction in his own actions alone, if only he could feel that his motives were as necessary as a natural force. In 1852 Müller moved to Brazil. For twelve years he worked as a high school teacher in Desterro (on the island of Santa Catharina not far from the coast of Brazil). In 1867 he had to give up this position too. The man of the new world view had to give way to the reaction that took hold of his school under the influence of the Jesuits. Ernst Haeckel described Fritz Müller's life and work in the "Jenaische Zeitschrift für Naturwissenschaft" (XXXI. Band N. F. XXIV, 1897). Darwin described him as the "prince of observers". And it was from a wealth of observations that the small but significant essay "Für Darwin" was written. It dealt with a single group of organic forms, the crustaceans, in the spirit that Fritz Müller believed must result from Darwin's view. He showed that the crustacean forms, which differ from each other in their mature states, are completely similar to each other at the time they hatch from the egg. If one assumes that, in the sense of Darwin's theory of descent, the crustacean forms have developed from an original crustacean form, and if one assumes that the similarity in the juvenile states of these animals is an inheritance from their common ancestral form, then one has united Darwin's ideas with Oken's ideas of the repetition of the creation history of the animal classes in the development of the individual animal form. Fritz Müller also accomplished this unification. He thereby brought the early forms of an animal class into a certain lawful connection with the later ones that formed from them through transformation. The fact that once an ancestral form of a creature living today looked like this and like that has caused this creature living today to look like this and like that at one time in its development. The developmental stages of organisms reveal their ancestors, and the nature of the latter determines the characters of the germ forms. In Fritz Müller's book, phylogeny and ontogeny are linked like cause and effect. This was a new move in the Darwinian school of thought. This is not weakened by the fact that Müller's cancer research was modified by Arnold Lang's later investigations.
[ 22 ] It had only been four years since the publication of Darwin's book "Origin of Species" when Müller's paper appeared in his defense and confirmation. He had used a single animal class to show how to work in the spirit of the new ideas. Seven years after the "Origin of Species", in 1866, a book appeared that was completely imbued with this new spirit, which used the ideas of Darwinism to illuminate the connection between the phenomena of life from a high vantage point: Ernst Haeckel's "General Morphology of Organisms". Every page of this book reveals the great aim of using the new ideas as the basis for a survey of the totality of natural phenomena. Haeckel sought a world view based on Darwinism.
[ 23 ] Haeckel endeavored to do his utmost for the new world view in two directions: he constantly enriched his knowledge of the facts that shed light on the connection between natural beings and natural forces; and he drew from these facts, with iron consistency, the ideas that would satisfy the human need for explanation. He is imbued with the unshakeable conviction that man can gain full satisfaction for all his soul's needs from these facts and these ideas. As it was clear to Goethe in his own way, so it is also clear to him in his own way that nature "works according to eternal, necessary, divine laws in such a way that the Deity himself could not change it". And because this is clear to him, he worships his deity in the eternal and necessary laws of nature and in the substances on which these laws operate. Just as the harmony of the laws of nature, which in themselves are connected with necessity, satisfies reason in his view, it also offers the feeling heart, the ethically and religiously inclined mind, what it thirsts for. In the stone that is drawn to the earth and falls towards it, the same divine is expressed as in the plant blossom and in the human spirit that dramatically shapes "William Tell".
[ 24 ] How erroneous it is to believe that the feeling for the wonderful beauties of nature is destroyed by a rational penetration into the workings of nature, by research into its laws, is shown so vividly by the work of Ernst Haeckel. The rational explanation of nature has been denied the ability to satisfy the needs of the mind. It may be asserted that wherever a person's emotional world is impaired by the knowledge of nature, this is not due to this knowledge, but to the person whose feelings are moving in the wrong direction. Anyone who follows the research paths of an observer of nature, such as Haeckel, with an open mind will also feel his heart beat faster with every step in the knowledge of nature. Anatomical dissection and microscopic examination will not destroy any natural beauty, but will reveal countless new ones. It is undoubted that in our time there is a struggle between reason and imagination, between reflection and intuition. Ellen Key, the intellectual essayist, is absolutely right when she sees in this struggle one of the most important phenomena of our time. (Cf. Ellen Key: Essays. Berlin, 5th Fischers Verlag, 1899.) Whoever, like Ernst Haeckel, digs deep down into the shaft of facts and boldly climbs up to the peaks of human knowledge with the thoughts that arise from these facts, can only find in the explanation of nature the reconciling power "between the two equally strong racers, reflection and intuition, which mutually bring each other to their knees". (Ellen Key, ibid.) Almost simultaneously with the publication in which Haeckel sets out with unreserved honesty his world view flowing from his knowledge of nature, with the appearance in 1899 of his "Welträtsel", he began to publish a work, "Kunstformen der Natur", in which he gives reproductions of the inexhaustible abundance of the wonderful forms that nature produces in its bosom, and which in beauty and diversity "far surpass all forms of art created by man". The same man who guides our intellect into the laws of nature directs our imagination to the beauty of nature.
[ 25 ] The need to bring the great questions of worldview into direct contact with the individual scientific investigations led Haeckel to one of those facts that Goethe says characterize concise points at which nature voluntarily gives us the basic ideas for their explanation. This fact presented itself to Haeckel when he investigated the extent to which the old Oken idea, which Fritz Müller applied to crustaceans, could be made fruitful for the whole animal kingdom. In all animals, with the exception of protists, which consist of only one cell throughout their lives, a cup-shaped or jug-shaped body, the so-called cup-germ or gastrula, is formed from the egg cell with which the creature begins its germ development. This cup-shaped germ is an animal form that all animals, from sponges to humans, assume in their first stage of development. This form has only skin, mouth and stomach. Now there are lower plant animals that have only these organs throughout their lives, which are therefore similar to the goblet germ. Haeckel interpreted this fact in terms of the theory of development. The gastrula form is an heirloom that animals have inherited from their common ancestor. Probably millions of years ago, there was an extinct animal species, the gastraea, which was built similarly to the lower plant animals still living today: the spongia, polyps, etc. From this animal species, everything developed. From this animal species evolved all the diverse forms that live today among polyps, sponges and humans. All these animals repeat their ancestral form in the course of their germinal history.
[ 26 ] An idea of immense significance was thus gained. The path from the simple to the composite, to perfection in the world of organisms was mapped out. A simple animal form develops under certain circumstances. One or more individuals of this form transform into another form according to the living conditions in which they find themselves. What is created through transformation is passed on to descendants. Two forms already exist. The old one, which has remained at the first stage, and a new one. Both forms can continue to develop in different directions and to different degrees of perfection. After long periods of time, an abundance of species arises through the inheritance of the forms that have developed and through new formations through adaptation to the living conditions.
[ 27 ] So, for Haeckel, what happens today in the world of organisms is connected with what happened in primeval times. If we want to explain any organ in an animal of our present day, we look back to the ancestors who developed this organ under the conditions in which they lived. What arose from natural causes in earlier times has been passed on to the present day. The history of the tribe clarifies the development of the individual. The causes of individual development (ontogenesis) thus lie in the development of the phylum (phylogenesis). Haeckel expresses this fact in his basic biogenetic laws with the words, the short ontogenesis or the development of the individual is a rapid and contracted repetition, a compressed recapitulation of the long phylogenesis or development of the species.
[ 28 ] Thus, all explanation in the sense of special purposes, all teleology in the old sense, is removed from the realm of the organic. One no longer looks for the purpose of an organ, one looks for the causes from which it has developed; a form does not point to the goal towards which it strives, but to the origin from which it has emerged. The method of explaining the organic has become the same as that of the inorganic. Water is not sought as a goal in oxygen, nor is man sought as a purpose in creation. One searches for the origin, for the actual causes of beings. The dualistic way of looking at things, which declares that the inorganic and the organic must be explained according to two different principles, is transformed into a monistic way of thinking, into monism, which has only one unified way of explaining the whole of nature.
[ 29 ] Haeckel points out with significant words that through his discovery the path has been found on which all dualism in the sense meant above must be overcome. "Phylogenesis is the mechanical cause of ontogenesis. With this one sentence our fundamental monistic conception of organic development is clearly indicated, and the truth of the theory of gastraea depends primarily on the truth of this principle... . For and against this principle every naturalist will have to decide in the future who is not content with the mere admiration of strange phenomena in biogeny, but strives to understand their meaning. This sentence also describes the unbridgeable gap that separates the older teleological and dualistic morphology from the newer mechanical and monistic morphology. If the physiological functions of heredity and adaptation are shown to be the sole causes of the formation of organic form, then at the same time every kind of teleology, dualistic and metaphysical approach is removed from the field of biogeny; the sharp contrast between the guiding principles is thus clearly indicated. Either there is a direct and causal connection between ontogeny and phylogeny or there is not. Either ontogeny is a compressed extract of phylogeny or it is not. Between these two assumptions there is no third! Either epigenesis and descent - or preformation and creation." (Cf. also Volume 1, p.286 ff. of this book.) Haeckel is a philosophical thinker. That is why, soon after he had absorbed Darwin's view, he energetically advocated the important conclusion that results from this view for the origin of man. He could not content himself with shyly pointing to this "question of all questions" like Darwin. Man is anatomically and physiologically no different from the higher animals, and consequently the same origin must be ascribed to him as to them. With great boldness, he immediately advocated this opinion and all the consequences that follow from it in terms of worldview. It was not doubtful to him that henceforth the highest expressions of man's life, the acts of his spirit, were to be considered from the same point of view as the activities of the simplest living beings. Observation of the lowest animals, the primitive animals, infusoria and rhizopods, taught him that these organisms also have a soul. In their movements, in the hints of sensations that they reveal, he recognized expressions of life that only needed to be enhanced and perfected in order to become the complicated acts of reason and will of man.
[ 30 ] What steps does nature take to evolve from the gastraea, the primordial intestinal animal that lived millions of years ago, to man? This was the comprehensive question that Haeckel set himself. He gave the answer in his "Anthropogeny", published in 1874. The first part deals with the germinal history of man and the second with the phylogeny. From point to point it was shown how the causes of the former lie in the latter. The position of man in nature was thus determined according to the principles of the theory of development. To works such as Haeckel's "Anthropogeny" one may apply the saying that the great anatomist Karl Gegenbaur pronounced in his "Comparative Anatomy" (2nd edition, 1870) that Darwinism as a theory receives back from science in abundance what it has given it in method: Clarity and certainty. For Haeckel, the Darwinian method also gave science the theory of the origin of man.
[ 31 ] The full extent of what was thus achieved can only be appreciated if one looks at the opposition with which Haeckel's comprehensive application of Darwinian principles was received by the supporters of idealistic world views. There is no need to look at those who turned against the "monkey theory" in blind faith in a traditional opinion, or at those who believe that all finer, higher morality is endangered if people no longer believe that they have a "purer, higher origin". One can also turn to those who are quite inclined to accept new truths. But even they found it difficult to find their way into this new truth. They asked themselves:
[ 32 ] Are we not denying our rational thinking if we no longer seek its origin in a general world reason above us, but in the animal kingdom below us? Such spirits pointed out with great zeal the points at which Haeckel's view still seemed to be let down by the facts. And these spirits have powerful allies in a number of natural scientists who, out of a strange bias, use their knowledge of the facts to continually emphasize where experience is not yet sufficient to draw Haeckel's conclusions. The typical representative and at the same time the most impressive representative of this natural scientist's point of view is Rudolf Virchow. The contrast between Haeckel and Virchow can be characterized as follows: Haeckel trusts in the inner consistency of nature, which Goethe believes comforts us over the inconsistency of human beings, and says to himself: if a principle of nature has proved to be correct for certain cases and we lack the experience to prove its correctness in other cases, there is no reason to put fetters on the progress of our knowledge; what experience denies us today can be brought to us tomorrow. Virchow is of a different opinion. He wants a comprehensive principle to gain as little ground as possible. He seems to believe that life cannot be made sour enough for such a principle. The contrast between the two minds came to a head at the fiftieth meeting of German naturalists and physicians in September 1877. Haeckel gave a lecture on "Today's development in relation to science as a whole."
[ 33 ] In 1894, Virchow felt compelled to say: "The ape theory was arrived at by speculation; one could just as easily have arrived at an elephant or a shaft theory." Virchow demands incontrovertible evidence for this view. However, as soon as something appears that is a link in the chain of evidence, Virchow seeks to invalidate its value in every possible way.
[ 34 ] The bone remains found by Eugen Dubois in Java in 1894 form such a link in the chain of evidence. They consist of a skullcap, a femur and some teeth. An interesting discussion arose about this find at the Leyden Zoological Congress. Out of twelve zoologists, three were of the opinion that the bone remains were from an ape, three that they were from a human; six, however, were of the opinion that we were dealing with a transitional form between humans and apes. Dubois showed in a lucid manner the relationship between the creature whose remains we had before us and the present-day apes on the one hand and the present-day humans on the other. The scientific theory of development must lay special claim to such intermediate forms. They fill in the gaps that exist between the numerous forms of organisms. Each such intermediate form provides new evidence for the relationship of all living things. Virchow opposed the view that the bone remains originated from such an intermediate form. At first he declared that the skull came from an ape, the thigh from a human. However, expert palaeontologists, after carefully examining the finds, were adamant that the remains belonged together. Virchow sought to support his view that the thigh could only have come from a human by claiming that a bone growth on it proved that it had been affected by a disease that could only have been cured by careful human care. The paleontologist Marsch argued that similar bone growths also occur in wild apes. Another of Virchow's assertions, that the deep constriction between the upper edge of the eye sockets and the lower skull roof of the supposed intermediate creature spoke for its ape nature, was contradicted by a remark by the naturalist Nehring that the same formation was found on a human skull from Santos in Brazil. Virchow's objections arose from the same attitude that led him to see pathological, abnormal formations in the famous skulls of Neandertal, Spy, etc., while Haeckel's fellow scientists considered them to be intermediate forms between ape and man.
[ 35 ] Haeckel did not allow any objections to rob him of his confidence in his way of thinking. He constantly treated science from the points of view he had gained, and he influenced the public consciousness by popularizing his view of nature. In his "Systematische Phylogenie, Entwurf eines natürlichen Systems der Organismen auf Grund der Stammesgeschichte" (1894-1896), he sought to present the natural relationships of organisms in a strictly scientific manner. In his "Natural History of Creation", which went through eleven editions between 1868 and 1908, he provided a generally understandable discussion of his views. In 1899, in his generally comprehensible studies on monistic philosophy "Welträtsel", he provided an overview of his natural philosophical ideas, which unreservedly set out the consequences of his basic ideas from all sides. In between all these works, he published studies on the most diverse special research, always taking account of philosophical principles and detailed scientific knowledge in the same way.
[ 36 ] The light that emanates from the monistic world view is, according to Haeckel's conviction, that which "dispels the heavy clouds of ignorance and superstition which have hitherto spread impenetrable darkness over the most important of all problems of knowledge, over the question of the origin of man, of his true nature and of his position in nature". This is how he expressed himself in the speech he gave on August 26, 1898 at the fourth international zoological congress in Cambridge "On our present knowledge of the origin of man". The extent to which his world view forges a bond between religion and science was vividly explained by Haeckel in his 1892 publication "Monism as a bond between religion and science. Confession of faith of a natural scientist".
[ 37 ] If one compares Haeckel with Hegel, the difference in worldview interests in the two halves of the nineteenth century emerges in sharp outline. Hegel lives entirely in the idea and takes only as much from the world of scientific facts as he needs to illustrate his ideal world view. Haeckel is rooted with all the fibers of his being in the world of facts and draws from it only the sum of ideas to which it necessarily urges him. Hegel always endeavors to show how all beings work towards ultimately reaching the summit of their becoming in the human spirit; Haeckel always endeavors to show how the most complicated human activities point back to the simplest origins of existence. Hegel explains nature from spirit; Haeckel derives spirit from nature. We can therefore speak of a reversal of the direction of thought in the course of the century. Within German intellectual life, Strauss, Feuerbach and others initiated this reversal; in materialism the new direction found a provisional, extreme expression, in Haeckel's world of thought a strictly methodical-scientific one. For that is the significant thing about Haeckel, that his entire research activity is imbued with a philosophical spirit. He certainly does not work towards results that are set up as goals of world view or philosophical thinking for any motives; but his method is philosophical. With him, science appears directly with the character of world view. The whole nature of his view of things has determined him to be a confessor of the most decided monism. He views spirit and nature with equal love. That is why he could still find the spirit in the simplest living beings. Yes, he goes even further. He searches for traces of the spirit in the inorganic mass particles. "Every atom" - he says - "possesses an inherent sum of force and is in this sense animated. Without the assumption of an atomic soul, the most ordinary and most general phenomena of chemistry are inexplicable. Pleasure and displeasure, desire and aversion, attraction and repulsion must be common to all mass atoms; for the movements of the atoms, which must take place in the formation and dissolution of every chemical compound, can only be explained if we attribute to them sensation and will, and it is on this alone that the generally accepted chemical doctrine of elective affinity is fundamentally based." And just as he traces the spirit down to the atom, so he traces the purely material-mechanical events up to the most sublime spiritual achievements. "The spirit and soul of man are also nothing other than forces that are inseparably bound to the material substrate of our body. Just as the power of movement of our flesh is bound to the form elements of the muscles, so the thinking power of our spirit is bound to the form elements of the brain. Our mental powers are functions of these body parts, just as every power is the function of a material body."
[ 38 ] But one must not confuse this way of thinking with that which dreams souls into natural beings in an unclear mystical way and allows them to be more or less similar to human beings. Haeckel is a fierce opponent of the world view that transfers human characteristics and activities to the outside world. He repeatedly expressed his condemnation of the humanization of nature, of anthropomorphism, with a clarity that could not be misunderstood. When he ascribes a soul to the inorganic mass or the simplest organisms, he means nothing more than the sum of the expressions of force that we observe in them. He adheres strictly to the facts. Sensation and will of the atom are not mystical soul forces for him, but are exhausted in what we perceive as attraction and repulsion. He does not mean to say that attraction and repulsion are actually sensation and will, but that attraction and repulsion are at the lowest level what sensation and will are at a higher level. Development is not a mere unfolding of the higher levels of the spiritual from the lower, in which they already lie hidden, but a real ascent to new formations (cf. above p. 403 ff.), an increase from attraction and repulsion to sensation and will. This basic view of Haeckel's agrees in a certain sense with that of Goethe, who expresses himself on the subject with the words: The fulfillment of his view of nature had become his through the recognition of the "two great driving wheels of all nature", polarity and increase, the former "belonging to matter, insofar as we think of it materially, the latter to it, insofar as we think of it spiritually; the former is in perpetual attraction and repulsion, the latter in perpetual ascent. But because matter can never exist and be effective without spirit, and spirit can never exist and be effective without matter, matter is also able to increase, just as spirit does not allow itself to be attracted and repelled."
[ 39 ] The adherent of such a worldview is content to deduce the things and processes that actually exist in the world. The idealistic world-views require entities for the derivation of a thing or process that are not found within the realm of the actual. Haeckel derives the form of the beaker germ, which appears in the course of animal development, from an organism that actually once existed. An idealist searches for ideal forces under whose influence the developing germ becomes a gastrula. Haeckel's monism draws everything it needs to explain the real world from this real world. He looks around in the realm of the real in order to recognize how things and processes explain each other. His theories, like those of the idealist, are not there for him to search for a higher level to the real, an ideal content that explains the real, but to make the connection of the real itself comprehensible to him. Fichte, the idealist, asked about the purpose of man. By this he meant something that is not exhausted in the forms of the real, the actual; he meant something that reason adds to the actually given existence; something that illuminates the real existence of man with a higher light. Haeckel, the monistic observer of the world, asks about the origin of man, and by this he means the real origin, the lower beings from which man has developed through actual processes.
[ 40 ] It is significant how Haeckel justifies the ensouling of the lower beings. An idealist would refer to rational conclusions. He would come up with the necessities of thought. Haeckel refers to what he has seen. "Every natural scientist who, like me, has observed the life activity of unicellular protists for many years is positively convinced that they also possess a soul; this cellular soul also consists of a sum of sensations, ideas and volitional activities; the sensations, thoughts and volitions of our human souls are only gradually different." The idealist attributes spirit to matter because he cannot imagine that spirit can arise from spiritless matter. He believes that spirit must be denied if it is not allowed to exist before it is there, i.e. in all those forms of existence where there is not yet an organ or a brain for it. For the monist, there is no such conceptual process. He does not speak of an existence that does not present itself as such externally. He does not assign two kinds of qualities to things: those that are real in them and express themselves in them, and those that are secretly in them in order to express themselves only at a higher level to which things develop. For him, what he observes is nothing more. And if what is observed develops further and increases in the course of its development, the later forms are only present at the moment when they really show themselves.
[ 41 ] The objections raised by the intellectual Bartholomew of Carneri, who, on the other hand, made an immortal contribution to the development of an ethics of this world view, show how easily Haeckel's monism can be misunderstood in this direction. In his work "Empfindung und Bewußtsein. Monistische Bedenken" (1893), he argues that the sentence: "No spirit without matter, but also no matter without spirit" would entitle us to extend the question to the plant, even to the next best boulder, and to attribute spirit to it as well. But there is no doubt that this would create confusion. It cannot be overlooked that consciousness arises only through the activity of the cells of the gray cortex. "The conviction that there is no spirit without matter, that is, that all spiritual activity is bound to a material activity, with the end of which it also reaches its end, is based on experience, while nothing in experience suggests that spirit is connected with matter at all." Those who describe matter, which betrays no spirit, are like those who attribute the ability to tell time not to the mechanism of the clock, but to the very metal of which it is made.
[ 42 ] Haeckel's view, correctly understood, is not affected by Carneri's concerns. It is protected from this by the fact that it adheres strictly to observation. In his "Welträtseln" Haeckel says: "I myself have never advocated the hypothesis of atomic consciousness; on the contrary, I have expressly emphasized that I imagine the elementary psychic activities of sensation and will, which can be ascribed to atoms, to be unconscious." What Haeckel wants is nothing other than that no leap should be made in the explanation of natural phenomena, that the complicated way in which spirit appears through the brain should be traced back to the simplest way in which mass attracts and repels. Haeckel regards the discovery of the organs of thought by Paul Flechsig as one of the most important findings of modern science. He emphasized that there are four areas for the central sensory organs in the grey cortical zone of the brain mantle, four "inner sensory spheres", the body feeling sphere, the olfactory sphere, the visual sphere and the auditory sphere. Between these four sensory foci lie the thinking foci, the "real organs of spiritual life"; they "are the highest tools of the soul's activity, which mediate thinking and consciousness ... These four foci of thought, distinguished from the intermediate sensory foci by a peculiar and highly intricate nervous structure, are the true organs of thought, the only organs of our consciousness. In recent times Flechsig has shown that in one part of these organs there are still found in man particularly intricate structures which are lacking in other mammals and which explain the superiority of human consciousness." (Welträtsel, 5. 212 f.)
[ 43 ] These explanations show clearly enough that Haeckel, unlike the idealistic world-explainers, is not interested in placing the spirit in the lower levels of material existence in order to find it again in the higher ones, but rather in following the simple phenomena up to the complicated ones by means of observation in order to show how the activity of matter, which expresses itself in the primitive field as attraction and repulsion, increases to the higher spiritual processes.
[ 44 ] Haeckel is not looking for a general spiritual principle because he is not satisfied with the general lawfulness of natural and spiritual phenomena, but he is completely satisfied with this general lawfulness for his needs. The lawfulness that expresses itself in the spiritual activities is of the same kind as that which appears in the attraction and repulsion of the mass particles. When he calls the atoms animated, this has a completely different meaning than when a proponent of an idealistic world view does so. The latter starts from the spirit, and takes the ideas he has gained from the contemplation of the spirit down into the simple operations of the atoms when he thinks them animated. He thus explains the phenomena of nature from the essences which he himself has first placed in them. Haeckel starts from the observation of the simplest natural phenomena and follows them up to the spiritual phenomena. He thus explains mental phenomena from laws that he has observed in the simplest natural phenomena.
[ 45 ] Haeckel's world view can arise in a soul whose observation extends only to natural processes and natural beings. Such a soul will want to understand the connection within these processes and beings. Its ideal can become to see through what the processes and beings say about their becoming and interaction themselves and to strictly reject everything that is added to an explanation of the events and workings from outside. Such an ideal deals with the whole of nature in the same way as one deals with the explanation of the mechanism of a clock. One does not need to know anything about the watchmaker, about his skill and about the thoughts he had when making the watch. You can understand the movement of the watch if you can see through the mechanical laws of the interaction of the parts. Within certain limits, such an understanding is all that is necessary to explain the movement of the watch. Indeed, one must be aware that the clock itself - as such - cannot be explained if one allows for any other explanation. If, for example, in addition to the mechanical forces and laws, one were to invent special spiritual forces that would move the hands of the clock forward in accordance with the course of the sun. Haeckel sees such forces invented in addition to natural processes as everything that is similar to a special life force or a power that works towards a "purposefulness" in beings. He does not want to think anything about natural processes other than what they themselves express for observation. His thought structure is to be that which is derived from nature. For the consideration of the development of the world view, this structure of thought presents itself to a certain extent as a counter-gift from the side of natural science to the Hegelian world view, which in its thought painting wants nothing to be drawn from nature, but everything from the soul. If Hegel's world view said: The self-conscious ego finds itself by having the pure experience of thought within itself, - then Haeckel's view of nature could reply: This experience of thought is a result of the processes of nature, is their highest product. And if the Hegelian world view did not feel satisfied by such a reply, the Haeckelian view of nature could demand: Show me such inner thought-experiences that do not appear like a mirror of what happens outside thought. A philosophy would then have to show how thought can come to life in the soul and really give rise to a world that is not merely the mental reflection of the external world. Thought that is merely thought cannot oppose Haeckel's view of nature. By way of comparison, the latter can claim that nothing can be found in the watch that indicates the person etc. of the watchmaker. Haeckel's view of nature is on the way to showing how, as long as one is merely confronted with nature, one can say nothing about it other than what nature itself says. In this respect, this view of nature makes a significant appearance in the course of the development of the world view. It proves that philosophy must create a field for itself which, beyond the thoughts gained from nature, lies in the self-creative realm of the life of thought. It must take the step beyond Hegel indicated in a previous section. It cannot exist in a mere procedure that remains in the same field in which natural science stands. Haeckel probably has not the slightest need to turn his attention to such a step in philosophy. His view of the world allows thought to come alive in the soul, but only to the extent that its life is stimulated by the observation of natural processes. What thought can create as a world view when it comes to life in the soul without this stimulation, that is what a higher world view would have to add to Haeckel's view of nature. One must also go beyond what the watch itself says, for example, if one wants to know the shape of the watchmaker's face. One therefore has no right to claim that Haeckel's view of nature should speak differently about nature itself than Haeckel speaks where he presents what he has positively observed about natural processes and natural beings.