He investigated the laws of the organisms in strict objectivity regardless of the purpose connection, and became a reformer of modern natural science through his comprehensive mind; he knew how to make use of the physical, chemical, anatomical, zoological, microscopical and embryological knowledge in an unlimited way. His view did not keep him from basing psychological qualities of the objects of his studies on their physical characteristics. It was one of his fundamental convictions that no one could be a psychologist without being a physiologist. But if a thinker went beyond the field of research in natural science and entered the realm of a general world conception, he was not in the fortunate position easily to discard an idea like that of teleological structure. For this reason, it is easy to understand why a thinker of the importance of Gustave Theodor Fechner (1801 87) would make the statement in his book, Zend-Avesta, or Concerning the Nature of Heaven and the World Beyond (1852), that it seems strange how anyone can believe that no consciousness would be necessary to create conscious beings as the human beings are, since even unconscious machines can be created only by conscious human beings. Also, Karl Ernst von Baer, who followed the evolution of the animals from their initial state, could not resist the thought that the processes in living organisms were striving toward certain goals and that the full concept of purpose was, indeed, to be applied for all of nature.
(Karl Ernst von Baer, Studies from the Field of Natural Science, 1876, pp. 73 & 82.) Difficulties of this kind, which confront certain thinkers as they intend to build up a world picture, the elements of which are supposed to be taken entirely from the sensually perceptible nature, were not even noticed by materialistic thinkers. They attempted to oppose the idealistic world
picture of the first half of the century with one that receives a11 explanation exclusively from the facts of nature. Only in a knowledge that had been gained from these facts did they have any confidence.
There is nothing more enlightening concerning the inner conviction of the materialists than this confidence. They have been accused of taking the soul out of things and thereby depriving them of what speaks to man"s heart, his feelings.
Does it not seem that they do take all qualities out of nature that lift man"s spirit and that they debase nature into a dead object that satisfies only the intellect that looks for causes but deprives us of any inner involvement? Does it not seem that they undermine morality that rises above mere natural appet.i.tes and looks for motivations, merely advocating the cause of animal desires, subscribing to the motto: Let us eat and drink and follow our physical instincts for tomorrow we die? Lotze (1817 81) indeed makes the statement with respect to the materialistic thinkers of the time in question that the followers of this movement value the truth of the drab empirical knowledge in proportion to the degree in which it offends everything that man"s inner feelings hold sacred.
When one becomes acquainted, however, with Carl Vogt, one finds in him a man who had a deep understanding for the beauty of nature and who attempted to express this as an amateur painter. He was a person who was not at all blind to the creations of human imagination but felt at home with painters and poets. Quite a number of materialists were inspired by the esthetic enjoyment of the wonderful structure of organisms to a point where they felt that the soul must have its origin in the body. The magnificent structure of the human brain impressed them much more than the abstract concepts with which philosophy was concerned. How much more claim to be considered as the causes of the spirit, therefore, did the former seem to present than the latter.
Nor can the reproach that the materialists debased morality be accepted without reserve. Their knowledge of nature was deeply bound up with ethical motivations. Czolbe"s endeavor to stress the moral foundation of naturalism was shared by other materialists. They all meant to instill in man the joy of natural existence; they intended to direct him toward his duties and his tasks on earth. They felt that human dignity could be enhanced if man could be conscious of having developed from a lower being to his present state of perfection. They believed that only a man who knows the material necessities that underlie his actions is capable of properly judging them. They argued that only he knows how to judge a man according to his value who is aware that matter is the basis for life in the universe, that with natural necessity life is connected with thought and thought in turn gives rise to good and ill will. To those who see moral freedom endangered by materialism, Moleschott answers: Everybody is free who is joyfully aware of the natural necessity of his existence, his circ.u.mstances, claims and demands, and of the limits and extent of his sphere of activity.
A man who understands this natural necessity knows also his right to fight his way through for demands that are in accordance with the needs of the human race. More than that, because only that freedom that is in harmony with the genuinely human will be defended with natural necessity by the species. We can be a.s.sured of the final victory over all suppressors in any struggle for human ends.
With att.i.tudes of this kind, with a devotion to the wonders of nature, with moral sentiments as described above, the materialists were ready to receive the man who overcame the great obstacle for a naturalistic world conception. This man appeared to them in Charles Darwin. His work, through which the teleological idea was placed on the solid ground of natural science, was published in 1859 with the t.i.tle,
The Origin of the Species by Means of Natural Selection, or the Preservation of Favored Races in the Struggle for Life.
For an understanding of the impulses that are at work in the evolution of philosophical world conception, the examples of the advances in natural science mentioned (to which many others could be added) are not significant in themselves.
What is important is the fact that advances of this kind coincided in time with the development of the Hegelian world picture. The presentation of the course of evolution of philosophy in the previous chapters has shown that the modern world picture, since the days of Copernicus, Galileo, etc., stood under the influence of the mode of conception of natural science. This influence, however, could not be as significant as that of the accomplishment of the natural sciences of the nineteenth century. There were also important advances of natural science at the turn of the eighteenth to the nineteenth centuries. We only need to be reminded of the discovery of oxygen by Lavoisier, and of the findings in the field of electricity by Volta and many others. In spite of these discoveries spirits like Fichte, Sch.e.l.ling and Goethe could, while they fully recognized these advances, nevertheless, arrive at a world picture that started from the spirit. They could not be so powerfully impressed by the mode of conception of natural science as were the materialistic thinkers in the middle of the nineteenth century. It was still possible to recognize on the one side of the world picture the conceptions of natural science, and on the other side of it, certain conceptions that contained more than "mere thought."
Such a conception was, for instance, that of the "force of life,"
or of the "teleological structure" of an organism. Conceptions of this kind made it possible to say that there is something at work in the world that does not come under the ordinary natural law, something that is more spiritual. In this fashion one obtained a conception of the spirit that had, as it were, "a
factual content." Hegel had then proceeded to deprive the spirit of all factual elements. He had diluted it into "mere thought." For those for whom "mere thoughts" could be nothing but pictures of factual elements, this step appeared as the philosophical proof of the unreality of the spirit. These thinkers felt that they had to find something that possessed a real content for them to take the place of Hegel"s "mere thought things." For this reason, they sought the origin of the "spiritual phenomena" in material processes that could be sensually observed "as facts." The world conception was pressed toward the thought of the material origin of the spirit through the transformation of the spirit that Hegel had brought about.
If one understands that there are deeper forces at work in the historical course of human evolution than those appearing on the surface, one will recognize the significance for the development of world conception that lies in the characteristic att.i.tude that the materialism of the nineteenth century takes toward the formation of the Hegelian philosophy. Goethe"s thoughts contained the seeds for a continuation of a philosophy that was taken up by Hegel, but insufficiently. If Goethe attempted to obtain a conception with his "archetypal plant" that allowed him to experience this thought inwardly so that he could intellectually derive from it such a specific plant formation as would be capable of life, he showed thereby that he was striving to bring thought to life within his soul. Goethe had reached the point where thought was about to begin a lifelike evolution, while Hegel did not go beyond thought as such. In communion with a thought that had come to life within the soul, as Goethe attempted, one would have had a spiritual experience that could have recognized the spirit also in matter. In "mere thought" one had no such experience.
Thus, the evolution of world conception was put to a hard test.
According to the deeper historical impulses, the modern time
tended to experience not thought alone, but to find a conception for the self-conscious ego through which one could be aware that this ego is firmly rooted in the structure of the world. In conceiving this ego as a product of material processes, one had pursued this tendency by simply following the trend in a form easily understandable at that time. Even the denial of the spiritual ent.i.ty of the self-conscious ego by the materialism of the nineteenth century still contains the impulse of the search for this ego. For this reason, the impulse with which natural science affected philosophy in this age was quite different from the influences it had had on previous materialistic currents. These earlier currents had not as yet been so hard pressed by something comparable to Hegel"s thought philosophy to seek for a safe ground in the natural sciences. This pressure, to be sure, does not affect the leading personalities to a point where they are clearly aware of it, but as an impulse of the time, it exerts its effect in the subconscious currents of the soul.
Chapter II.
Darwinism and World Conception
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 a.s.sume 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 pa.s.s 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.
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 circ.u.mstances 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 circ.u.mstances. 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 compet.i.tion. 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.
Darwin was led to this thought through the work of the social economist Malthus ent.i.tled Essay on the Principle of Population (1798). In this essay the view is advanced that there is a perpetual compet.i.tion 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.
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 princ.i.p.ally 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 sh.o.r.es 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 const.i.tution 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 circ.u.mstances. 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 circ.u.mstances 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 a.s.sume 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.
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 a.s.sumed 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 enn.o.bled. . . . 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.
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.
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 a.s.sumed.
In every such case one had to admit a miracle.
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 a.s.sumed. 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.
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 a.s.sumes 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 a.s.sume 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 circ.u.mstances then come to pa.s.s 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.
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 ac.u.men 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.
In another pa.s.sage 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.
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 circ.u.mstances." 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.
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 surpa.s.s 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
pa.s.s 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.
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 ac.u.men."
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 acc.u.mulated 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: 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?
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, trans.m.u.tation of forms and the struggle for life?
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!"
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.
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 Cla.s.ses 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 cla.s.ses of animals. In the beginning it shows only the organs of infusoria, thereupon gradually a.s.suming those of the polyps, jellyfish, sh.e.l.lfish, snails and so forth. Conversely, then, I also had to consider the cla.s.ses 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 cla.s.s 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 coc.o.o.ns 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 repet.i.tion of the history of the creation of the animal cla.s.ses."
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 att.i.tude also prevailed in his treatment of the law of the repet.i.tion of certain animal forms in the ontogeny of others mentioned above.
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 cla.s.s 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 Muller (1821 97) in his thoughtful essay, Facts and Arguments for Darwin. Muller 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 Muller 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 Muller in the Jenaische Zeitschrift fur Naturwissenschaft (Vol. x.x.xI N.F. XXIV 1897).
Darwin called Muller 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 repet.i.tion of the history of the creation of the animal species in the evolution of the individual animal form.