The History of Biological Theories

Recently the work of Kammerer has aroused much discussion. He had experimented for many years with the spotted salamander. Exposing these animals to special con- ditions of temperature, humidity, &c., on a background of a chosen colour, and also by performing on them definite operations, he claimed to have produced unmistakable alterations in the character of the organism. He asserted further that, by careful breeding, he had obtained con- clusive proof that these acquired characters are inherited. Many scientists are sceptical about his results.

To Darwin the problems of heredity seemed clear and simple. With us the more they are analysed, the more complex they become. No observation, experiment, or intellectual speculation can alter the fact that each organ- ism is an autonomous individual ; it contains within itself the laws of its existence ; and, in spite of the influence of its surroundings, it develops along its own lines. As to the nature of the directive force we know nothing. E idea of Natural Selection and Darwin's theory JL of evolution are very closely connected. If natural selection does not occur, Darwinism must be abandoned. There was from the first one strong objection to the theory of natural selection. Suppose a new and advantageous variation to appear, the animal bearing it must mate with another which has not varied hence the descendants would only inherit the advantage in a minor degree. Attempts were made to meet this difficulty. Could a factor be found that would separate the new variety from the non-varying form ?

Wagner, the German traveller and ethnographist, sug- gested (1869) that, among the higher animals, the origin of new species is assisted by migration. If a new variety migrates into a neighbourhood where the type does not exist, it can develop there under new conditions, and it does not have to compete with the type for existence. So a local variety is formed, representing a first step in evolu- tion, and the process is continued in the same manner. Wagner only applied his theory of migration to the higher animals. He thought that the lower forms of life are altered by the direct influence of the environment. Among those who favoured this theory were the American pastor, John Gulick (1905), A. E. Ortmann (1896), and P. Matschie (1895). In his later work Wagner himself considered evolution much more from the physiological point of view.

In 1 88 1 a book was published dealing with the struggle for existence within the animal body. It attracted a good deal of attention, and Darwin called it the most important book on evolution of its time. The young author's teachers, Haeckel and Weismann, gave it their approval. This writer, W. Roux, was already known by his work on the branching of the blood-vessels, which he had accounted for on purely mechanical principles based on the blood pressure on their walls.

Roux asserted that the struggle for existence between plants and animals may indeed account for the develop- ment of the coarser bodily features ; for example, for the development of a definite type of foot, or the coarser features of the eye; but it can never account for the evolution of the finer details of structure all those details so purposeful in every point. The thigh bone is constructed in correlation with the weight of the body and the way in which that weight is supported. But more than this ; the finer systems out of which it is made are fitted together, much as a clever engineer might have fitted them, if he had set out to construct a column out of the least possible material, that should support a given weight. Similar fine details of structure, most admirably suited to their purpose, are to be found in every part of the body. The ordinary idea of the struggle for existence does not account for all this. One well placed Haversian system in its thigh-bone does not give any animal an advantage in the struggle ; there are hundreds of thousands of them, and it is the right placing of this large number that gives to the bone its strength. * Roux suggested that such perfection is due to an inner struggle for existence between the various elements of the body. "Imagine bone a homogeneous substance, and every part of it equally well nourished. If the weight rests on it, and muscles expand it in certain directions, some parts will be more used, and so more stimulated, than others. Those parts grow stronger, and rob neighbouring parts of both room and nourishment. They survive, the parts less favourably situated degenerate. Thus bone gradually evolves a structure, at once strong and well suited to its work. Other organs evolve in the same way. A mechanical

theory to account for the finer structure of each portion of the body may thus be formulated. To this process of strengthening and detailed differentiation Roux gave the name 'functional adaptation'. The Darwinists accepted the new idea gladly. Roux himself admitted that his theory was to be regarded as an elaboration of the ideas of Haeckel and Preyer. Some critics asserted that the inner conflict between different components of the body is not analogous to the struggle for existence between individuals. Darwin himself, how- ever, not to speak of his followers, had used the idea of a struggle for existence in many very different ways. There were others again who suggested that Roux's distinction 1 between external and internal 'purposiveness' is artificial. The talon of a bird of prey, for example, is eminently suited to its purpose of grasping the victim, and yet we cannot explain its structure as due to internal selection. These objections, however, were not raised until a time had come when doubt was being thrown on the whole idea of selection, and Roux himself was directing the attention of scientists to very different phenomena.

In his first book in support of the Darwinian theory (1868), Weismann expressed views akin to those of Nageli and Wagner. They were not derived directly from Darwin. He attempted to reconcile Wagner's migration theory with Darwin's theory of natural selection. In 1876 he published another book, in which he said that both Nageli's idea of a tendency towards perfection, and Haeckel's mechanistic explanations, contain some germs of the truth. Weismann now suggested that there are only two alternatives. Evolution is caused either 'by the action of a phyletic force, or by the reaction of the organism to external influences'. He favoured the latter view, which shows us that at this time his opinions were not far from Lamarckian. Further, he pointed out that the alternative

view did not lead to any very satisfactory solution of the problem. Nageli had also suggested that the organism reacts to external influences, but that, in addition, there exists a 'phyletic force', i.e. some inner organization, which determines the nature of that reaction. Weismann did not absolutely reject such a fundamental controlling force, and this gave a certain lability to all his expressions of opinion. He feared, however, that this 'phyletic force' was a distant relative of the old 'Vital force', and this he was anxious to avoid at all costs.

Nageli's belief in the dual nature of living substance was the impetus, the starting-point of all his philosophy, but Weismann's belief in a 'phyletic force' was sterile. What Nageli regarded as a mere hypothesis, a deduction from his materialistic views, Weismann presented as a fact, an axiom, and all his further deductions depended upon it. He regarded protoplasm as the bearer of life. Life will continue, as long as that endures. If we examine the body of an amoeba, which consists of a single cell, and reproduces by fission, we see that it never dies a natural death. There is no corpse. The amoeba passes over into its two daughter cells. Hence the protozoa are immortal, apart from external accidents. Unfortunately this is not true of the multicellular animals, one of whom is Man. Here only the reproductive cells survive the death of the individual ; their protoplasm passes directly (by continued division) into the protoplasm of the offspring, and so ever onward, to succeeding generations. Hence the protoplasm of the generative cells never dies. The body is a mortal shell clothing the immortal sex cells.

According to Weismann, then, death is not a necessary attribute of life. It is only an 'adaptation' which did not exist originally, but has been gradually evolved. The reason for this evolution is that, for the whole animal creation, eternal life is a 'purposeless luxury'! Other animals besides those actually in existence want to live. Hence, as a rule, the higher organisms only live long enough to ensure the lives of their offspring. Insects, whose care for the young ends with the laying of the eggs, very often die as soon as the eggs are laid. Man, on the other hand, is granted a more extended life that he may bring up his children, who are for long incapable of an independent existence.

We listen with lively curiosity to Weismann's views. We almost agree with them. They sound unanswerable. We do not at first notice how much of its living content this theory of immortality has had to sacrifice. But on reflection do the facts fit the theory ? During conjugation of infusoria, a portion of the body substance is eliminated. Does not this represent the missing corpse ! x In the hands of Darwin, his theory was a philosophy based on a very wide experience. In the hands of Haeckel, it became a medium for combating social reaction. In the hands of Weismann, with his theory of immortality, the evolu- tionary theory, unnoticed either by Darwinists or anti- Darwinists, put on a frock coat; it shook off everything elemental, everything passionate, everything human ; and became merely a polite theory, interesting for discussion in the salon !

Weismann took Nageli's theory that there is a difference between idio- and stereoplasm, and developed this idea. The body, according to him, is made up of different com- ponents the red blood corpuscles are one component, eye colour another, a spot on the butterfly's wing, a birth- mark in man, are examples of others. As the child's brick castle is built up of single bricks, so is the body built up of these components. If one stone of the set is lost, the castle cannot be built. If one component is missing, the building up of the living body is impossible. But the living body is vastly more complex than the box of bricks. First of all, the separate components are not dead stones by any means, for they are able to increase by division, so that each quality can be duplicated over and over again. Secondly, reserve components are tucked away in various

1 R. Hertwig, 'Uber die Konjugation der Infusorien, Abb. Akad. Miinchen, corners of the body in the leg of the Triton the com- ponents of that leg are produced, for example ; but there are also hidden away in other parts of the body various leg 'qualities' which only develop when the Triton loses his leg. Thirdly, all the components of the future body lie hidden in the egg-cell. When this cell divides into two, four, and more segments, the components are separated to the right and to the left, above and below, to the front and to the back. Head components travel to the point where the head will develop, foot qualities to that spot where feet shall develop, and so the mature body gradually arises. These qualities, however, possess an inherited power of division, and hence innumerable groups of qualities arise. These are not all used up during develop- ment ; many groups wander into the newly formed repro- ductive cells, or to places where a new body may arise by budding.

We must picture these components as real, extremely small granules of matter, which are aggregates of even smaller granules ; they are all present in the egg nucleus. It is almost impossible to give any short description of this extremely complicated network of components, each component represented by a granule of living substance. No army is so numerous, nor led in so orderly a manner, as Weismann's hypothetical granules. Millions of them lie dormant within the egg, arranged according to definite laws, in companies, battalions, and groups of higher and higher order. When development begins, they separate just at the right moment, until in the cells of the mature tissue only a few are present, and these live, struggle, and die there. Millions of reserve granules are waiting to replace those that die, while new armies of them arise in the reproductive organs. These leave the body with the egg to form a new body essentially similar in constitution.

Thus Weismann came to the conclusion that all the components of the adult body lie hidden in the egg and sperm nuclei. He called the nuclear protoplasm which contained these components, the germ-plasm. During segmentation it divides to form new nuclei, and it is always present in any part of the body which can produce a new organism in the reproductive cells, in the cambium of plants, and in all those parts which may undergo re- generation. In other parts of the body the nuclear proto- plasm only contains a few of these qualities such proto- plasm Weismann called somatoplasm.

Weismann wrote many books in which he developed this theory of the germ-plasm. In 1892 he rounded off and completed his, theory in a large work dealing with heredity, which fascinated contemporary biologists. It was, of course, obvious that his pre-supposed granules biophors, determinants, ids, idants, as he called them were mental concepts, but they were accepted almost as ob- jective realities by a large part of the scientific world, who passed them on to the lay public.

Is the whole organism already present in the egg, or is it only formed during development ? This problem had already occupied the early Christian fathers, and attempts to elucidate it had exercised the embryologists of the early part of the century. Here, in this theory of Weismann's, the question is answered in conformity with the views of the preformationists. If all the qualities of the mature organism are already present in the egg, in the form of minute granules, what is this but a revival of the doctrine which still makes us smile when we study the Natur- philosophen of the eighteenth century ? Weismann and his contemporaries were hardly conscious that he was going back to their conceptions. He imagined himself far superior to Bonnet, because he did not think that the egg contains a man in miniature. Had he not advanced to the idea of granules ? What progress ! As if Bonnet had ever taught anything different ! He too had only asserted that all the qualities of the adult must be already present in the egg, he too had the modern 'granules' in mind, and by them he explained regeneration, even as Weismann did.

When Weismann produced his theory of an immortal germ-plasm, round which the rest of the body forms a shell which is only in mechanical continuity with the re- productive cells, he inferred that characters acquired during the life time of the individual must die with that individual, since they merely represent a change in the body, in the somatoplasm. The germ-plasm, shut up in the reproductive cells, cannot be influenced by bodily changes (due to injury, to exercise, to habitat and the like). Only those changes which arise in the germ-plasm itself can affect the heredity of the organisms. He was able to prove that injuries (mutilations) are not inherited; nor did he believe that changes due to use and disuse (the so-called functional changes) are inherited.

In the discussions which followed the publication of his views, Weismann admitted that the effect of the action of the environment on the body might be inherited, if the germ-plasm were influenced too. Such changes, though directly due to the action of the environment, would in that case be inherited. The whole discussion, however, was fantastic. Weismann's denial of the inheritance of acquired characters was not due to any new insight into natural processes. He deduced it from a theory which was, in its turn, only a deduction from the unproven hypothesis that there is a difference between the germ- plasm and the somatoplasm.

In this matter of the inheritance of acquired characters biologists were separated into two camps. Those who believed in such inheritance were called Neo-Lamarckians, while Weismann's followers were called Neo-Darwinians. Natural selection, according to Weismann, is the only factor which can produce new species. That part of Darwin's theory which rests upon the assumption of the inheritance of acquired characters must be rejected. We must explain the origin of new species with the help of inborn variations only. Those which are useful will be retained by natural selection, the others will disappear. Hence the qualities of any organism are merely those

qualities which have been found useful to it they have no other meaning: 'The eye of the frog is a very imperfect instrument when com- pared with the eye of an eagle or of a man ; but it is good enough for seeing the crawling fly or the wriggling worm good enough, that is, to ensure the nourishment of the species. Even the eye of the eagle is not an absolutely perfect optical instrument, but it enables the bird to discover its prey with certainty while hovering high up in the air, and this is enough to ensure the existence of the species ; hence any further improvement as the result of natural selection is excluded' (A. Weismann, Aufsdtze uber Vererbung und verwandte biologiscbe Fragen, 1892).

Arguing thus, Weismann selected the one 'almighty' principle of evolution ; by doing so he made it unreal. Darwin the observer, believed that he had actually seen natural selection in operation, and pictured its influence as controlled by other factors. In this belief he was mistaken ; his 'utilitarianism', and his theory of natural selection, were really nothing but logical principles, by means of which he was endeavouring to interpret nature. Weismann seized on these principles, and set them up as axiomatic truths. He abandoned natural selection as a fact of experi- ence and made it a logical principle by means of which all the qualities of the organism can be and must be explained.

The doctrine of chance could be taken no further ; all that now remained was to look for some compromise with reality. Inspired by Roux's ideas, to which we have already referred, Weismann published a new hypothesis in 1895. He developed the idea further, and a year later suggested that there is a struggle for existence within the germ a process which he called 'germinal selection'. He now endowed his hypothetical granules with new capacities. He supposed that their size and vigour were proportional to the size of the component they produced, and dependent upon the amount of food they received. Those granules which are by nature more robust will attract to themselves more nutriment, and will grow strong at the expense of

their weaker neighbours hence the growth and develop- ment of the one results in the weakening and decay of the other. Let us assume, for example, that an animal becomes accustomed to life in darkness. Its eyes become useless, even harmful, since they can be so easily injured. Among its descendants some will by nature have weaker sight. These are as well equipped for the struggle for existence as are the sharp-sighted, since sight is now useless. There will be indiscriminate breeding between the weak and the strong of sight, and this will lead in time to de- generation of the organ of vision. Weismann called this indiscriminate breeding panmixia, and endeavoured to explain the origin of rudimentary organs as due to this cessation of selection.

Some of Weismann's critics doubted how much pan- mixia would explain, and particularly whether a struggle between individuals could ever cause an organ to disappear entirely. Weismann admitted the validity of this objec- tion, but thought that his theory of germinal selection would solve the difficulty. In the case referred to, for example, the granules determining weak sight are less potent than granules determining the other qualities of the animal; in the struggle for nourishment which takes place during development, the 'sight' granules are con- sequently defeated ; this continues until, ultimately, they are totally destroyed. The result is that the eye completely disappears in animals who continue to live for generations in total darkness.

It was also suggested that this struggle for existence within the germ would assist in the production of favour- able variations, and in the accentuation of such variations ; in the origin of whole groups of organs, of monstrosities, mutations, specific talents, &c. Thus in the end Weismann admits that external con- ditions (temperature and the amount of food, for example), can produce modifications, not only of the body itself, but also of the germ-plasm, and that some of these may be hereditary.

For the influence of the environment extends to the granules in the germ-plasm, strengthening some and weakening others. It can happen, for example, that, for some reason or other, the strength of one granule will increase. It begins to oppress its neighbours ; this causes an increased development of the organ which those granules represent. This increased development enables the animal to be more successful in the struggle for existence ; this leads to a still greater nourishment of the granules which represent the organ in question, and hence to an even greater development of that organ in the succeeding generation, and so the process continues. In this way, according to Weismann, we can explain why variations do not sway about blindly, now here, now there, but follow a definite course, which is advantageous to the animal.

Weismann's theory rapidly gained and almost as rapidly lost favour among men of science. There are to-day very few who believe in his distinction between the germ-plasm and somatoplasm, or in the immortality of the protozoa ; in the omnipotence of natural selection, or in determinants, ids, and idants although this dead material is still dragged into text-books. Nevertheless Weismann's influence was great, and its effect was felt beyond the world of biology. It led to a fuller investigation of the problems of heredity, and, further, to the application of the Darwinian theory to the study of the cell-nucleus. He impressed upon investi- gators the idea that the organism must be resolved into its component parts ; by denying the omnipotence of natural selection, he paved the way for Neo-Lamarckianism ; finally, those who in the end became sceptical about the Darwinian theory began by being sceptical about Weis- mann's ideas. It was his influence, too, which made bio- logical thought become so much more superficial, as it became fashionable to refer every problem to the pheno- mena within the cell. Haeckel and Weismann were very strongly contrasted characters. Both were the apostles of

Darwin. One became the leading figure in anatomy and embryology, the other the guiding force in histology. Haeckel silenced von Baer, the embryologist, and returned to the ideas of Meckel. Weismann ignored Baer, the epigeneticist, and went back to the ideas of the tedious and insipid Bonnet. FESCARTES held that only human beings possess souls. He compared animals with the automata which were so popular in his time. In the eighteenth century this theory was challenged, and many thinkers claimed that animals have souls. A hundred years before Darwin, Condillac (1755) propounded a theory of the origin of the animal soul. He believed that every animal has at the beginning as much intelligence as has a human being, but that its development is retarded by want of experience.

'Objects produce impressions upon the animal, he has sensations of pain and pleasure. These cause the first movements of the animal. To begin with these are very uncertain, and are not under his control, for he does not know how to control them. The same desires, the same necessities, return again and again ; the movements are repeated so often that there is no more trial, no more uncer- tainty. The animal has become accustomed to act and to judge. In this manner desires produce impressions on the one hand, the corresponding actions on the other.'