The History of Biological Theories

rife. The philosophy of Mill, the ideas of democracy, the history of man, the discoveries of palaeontology, the belief that there is progression displayed in the various series of animals and plants all were witnesses pleading the same cause. Darwin's teaching really represents a slight re- action against this belief, not because he rejects the idea of progress, but because he points out that progress is not inevitable, that there may be stagnation or even retro- gression.

The word 'evolution' is often taken to mean progressive evolution, but Darwin himself understood by it merely a continuous change. He pointed to the parasites to show that this change is not necessarily progressive. They were more complete and perfect as independent organisms, and they became degenerate and simplified when they adopted a parasitic life. He also pointed out that the advance of one organ of the animal body often entails the degeneration of others. Thus many animals, and even man himself, possess organs which are in decline, as well as some which are very highly developed.

Darwin's theory was a very empirical one. Consequently the connexion between it and those ideas of progress which were so prevalent was not clear. Darwin himself definitely rejected the theory that progress is inherent in the scheme of nature, and declared that such progress as occurs must be due to definite processes at work. Hence the Darwinists did not accept any of those theories which assume that evolution is identical with progress. On the other hand, to those who were antagonistic to all such ideas, they pointed out that the facts of palaeontology and embryology prove that progress does most certainly occur in Nature.

The same material was used by the anti-evolutionary school however, to prove, firstly, that Nature progresses and evolution proceeds according to a pre-ordained plan, and, secondly, to show that progress in the Darwinian sense is not proved by the facts of palaeontology. Hence it came about that two investigators, holding diametrically opposite views, appealed to the same facts in argument. In 1862, for example, Huxley was affirming that the facts of palaeontology support Darwin's views; a year later O. Volger, working on the same material, claimed that the fossil records do not reveal any continuous progress, since even the oldest rocks contain some fairly advanced forms.

Haeckel made great use of the idea of rudimentary organs. He forgot that De Candolle had built up the greater part of his idealistic morphology upon the assump- tion that there are such organs, and thought that this idea of rudimentary, and hence purposeless, organs origi- nated with Darwin ! The idea seemed to Haeckel to be extremely important, for it apparently disproved the assumption that in Nature a definite purpose is revealed. Haeckel therefore called the study of such organs and functions Dysteleology.

The custom arose of calling whole animals and plants 'degenerate'. They were presumed to have sunk from a higher to a lower plane of existence. It has been very definitely asserted that parasites are forms which have adapted themselves to a less complex way of life, but apart from this group few naturalists have believed that there has been any widespread degeneration among animals. Dohrn was, however, an exception. He tried to prove that the lower fishes have arisen by degeneration from the more advanced forms ; that the coelenterata and the protozoa are both degenerate groups (1875).

In the literature the word 'degeneration' is not always used in the same way. To Buffon, the French biologist, it meant merely a change of form. The French psycho- logist, Morel, used the word degenerescence (1857) to describe any 'pathological departure from the original type. No matter how simple the departure may be, when once it has arisen it is extremely infectious. Any one attacked in the slightest degree will gradually lose the power of playing his part in human society. All hope of mental progress is enaangered, not only for him but for his descendants'. (B. A. Morel, Traite des Degenerescences,

1857.) Thus a new variety of the human race may arise, but it is a variety doomed to speedy extinction. Degeneracy in the human race is to be recognized by certain bodily signs : lack of symmetry between the two halves of the face; the lack of ear muscles; squinting; harelip, and other so-called 'stigmata'. Lombroso and a French physician Fere were later to devote a great deal of attention to this aspect of degeneracy. According to the Darwinian theory such manifestations are to be regarded as simplifications rather than as deteriorations. Darwin did not believe that some forms are better adapted to life, others less well fitted. Each species is suited to its own particular conditions, and some are more, others less, highly differentiated. He believed that the tape-worm, which has no head, no sense-organs, and no digestive tract, is as well suited to its environment as is the more complex free-living worm to its more variable surroundings. We cannot say whether Darwin was right. Are we to regard all the species which occur as 'natural' ? Is it not better to look upon some as degenerate, or, to express it more forcibly, pathological? The idea of pathological forms is quite foreign to Darwinism. There is no place for any such in a scheme where the struggle for existence sees to it that only the fittest survive. The word 'abnormal' has no meaning in the Darwinian philosophy, for, according to that, everything that exists is normal.

There has been little further investigation of this question of abnormal species, though it is often assumed that such exist. Virchow asserted (1886) that there are pathological races (bulldogs and pugs for example), as well as patho- logical genera and species ; he gave examples from among the parasitic Crustacea. Another discussion of this question of the occurrence of abnormalities, is found in the work of von Kennel (1901). He directs attention to the horned hog of Celebes (Sabyrussa alfurus), which has long curved upper canines which pierce the upper lip ; to the narwhal, with a long

tusk curved like a corkscrew ; to Anarhichas frontalis, a New Zealand bird with a beak the apex of which is bent to the right at an angle of 30. The whole question deserves more thorough study. It seems possible that the large mesozoic reptiles, that such structures as the peculiar outgrowths on the heads of some insects, that all species which are either abnormally large or abnormally small when compared with the average, are in a sense patho- logical. A new philosophy must prevail, however, before such problems can become the subject-matter of science.

Biologists and non-biologists alike have been more con- cerned to suggest the causes of degeneration than to study the subject itself. Weismann, however, did important work in this field, and aroused great interest. His thesis was that the struggle for existence is the only force making for progress. Directly it ceases the whole organism, or some part of the same, begins to degenerate. There were various other alleged causes of deterioration. Among these the pairing of nearly-related individuals was the chief. C. K. Sprengel drew attention to this question as early as 1793, when he showed that even in hermaphro- dite plants there is very often cross-pollination. Earlier students of mental disease, Esquirol and Spurzheim, for example, had also asserted that the marriage of near rela- tives often leads to degeneracy in the offspring. Diverse diseases were said to result from such marriages sterility, monstrosities of all kinds, harelip, albinism, scrofula, apoplexy, epilepsy, idiocy, goitre, paralysis, blindness, deafmutism.

Darwin once more turned the attention of biologists to this problem. His views were not as extreme as those of Esquirol, but he asserted that the mating of individuals who are rather different from each other is advantageous for their offspring. It is now apparent that inbreeding is not as dangerous as was once thought. Facts have come forward indicating that mating of near relatives is not dangerous, except in so far as family failings appear intensified in the off- spring. 1

Another suggestion has been made that, when organisms are degenerating, they follow the same order in their decay as they did in their development, degenerative processes following the biogenetic law in the reverse direction. The zoologist Lameere and the psychologist Ribot were among those who favoured this view, but it did not lead them to any very striking results. Outside the realm of biology the idea of degeneration became firmly established. Psychologists, students of race, lawyers, novel writers all referred to it. Zola introduced it into the novel, Ibsen into drama, and Max Nordau into literary criticism, the latter developing it to absurd lengths.

1 See L. Woltmann, Politiscbe Anthropologie, Eisenach and Leipzig, 1903, pp. 105 sqq., which gives the different views that have been held about this matter. ERNST HEINRICH HAECKEL was born at Pots- dam in 1834. In his youth his favourite books were the works of Humboldt and Schleiden. He studied medicine under the best teachers of his time and attended Alexander Braun's botanical lectures. In these the cell theory, the facts of development, and a somewhat ideal- istic morphology were presented in a philosophic manner. Miiller's lectures on physiology were equally philosophical, and Haeckel attended those too. At Wiirzburg his teaching was more 'modern'. Leydig and Kolliker were laying the foundations of modern embry- ology and histology. The more old-fashioned naturalistic philosophy meant nothing to them ; it merely awakened youthful memories. In Wiirzburg Haeckel heard Virchow's lectures on The Cell\ these provided new material in support of the cell theory, and presented it in an unmis- takably materialistic light. Leaving Wiirzburg, Haeckel went to Italy, where he nearly became a landscape painter! He was still, however, unconscious of any special bent. In Sicily he called to mind the encouragement given to him by Johannes Miiller, and threw himself into the study of the Radiolaria. In 1862 he published a large monograph upon them, in which he mentioned Darwin's theory with approval. The next year, at a congress at Stettin, he took up arms for the theory. From then onward he devoted all his energies to its establishment. Completely under its sway, he wrote with his friend Gegenbauer a two-volume book: General Morphology. This was intended to win over German biologists to Darwinism. The attack, however, did not succeed. The German pro- fessors treated the book as a belated offshoot of the long

discarded Naturphilosophie, and paid little attention to it. Disappointed with this want of success in the intel- lectual world Haeckel determined to appeal from the academic class to the public. Taking the advice of friends, he published a work, The Riddle of the Universe, which was extremely successful, and probably did more than any other book to spread the Darwinian theory. It went through ten German editions and was translated into eleven different languages, including English. Haeckel was now famous.

Haeckel was upright and full of energy, but blunt and harsh to opponents. The world of science was for him a battle-ground, and every word of his was an attack. He was a great contrast to the tranquil and learned Darwin or the elegant and critical Huxley. Men like Haeckel are born only in Germany the blood of Luther, Bismarck, and Nietsche flowed in his veins. Looking for a man of similar temperament we should select Fichte, the protagonist of the freedom of the German University. Fichte had no great breadth of vision but tremendous powers of persuasion. He said of himself: 'I have only one passion, one need, one desire to influence others.' Fichte expressed, not only his own temperament, but that of all great prophets, including Haeckel, in the following words :

'You say a philosopher must remember that he is merely an individual, liable to make mistakes, and that he must be ready to learn from others. Do you know what sort of a person you are describing? a man who, in his whole life, has never known what it is to feel absolute conviction/ Haeckel shared this feeling. He was never shaken by doubt. No teaching altered his views. His belief in Dar- win's theory underlay his every activity. His conviction was so strong that he allowed nothing to hinder him from proclaiming it. The scientific world ignored his fantasies. Darwin, the peacemaker, tried by letter to tone down his enthusiasm, but in vain. Huxley admonished him>

both publicly and privately. His German friends sought to dissuade him. It was all useless, Du Bois Reymond's humour left him unmoved. The indignation of His, Goette, Rutimeyer, Wigand, Semper, Claus, Loofs and others left him cold. He paid no attention to the blows aimed at him. To the end he remained the bold defender of Darwinism that he had been in his early days. He was a very prolific writer, and like a true German he liked long books. But whatever the ostensible subject of his book, his ceterum censeo remained the evolution theory. He would have set heaven and hell in motion to win freedom for science freedom, that is, for scientists to preach evolution.

He turned his attention to the sea sponges. This resulted in a curious play with names, by which he endeavoured to prove that there are no species among the sponges, and hence that they provide a wonderful con- firmation of the theory of evolution. When he wrote about Goethe he attempted to prove that he was in favour of evolution and a forerunner of Darwin. He rejected religion, for had he not a higher ideal evolution! When Bismarck visited Jena, Haeckel suggested that they should honour him by giving him the honorary title of 'Doctor of Phylogeny'. Evolution is the life-blood of his books. Take away the ideas about evolution and nothing is left but a lifeless husk, a mass of high-sounding words, of dull descriptions, of many-coloured pictures all empty and devoid of life. We look in vain for depth of feeling, for fineness of conception, for humour, style, self-distrust in short, for any spark of humanity. If you read one book of HaeckePs you have read them all.

Yet he was, withal, a many-sided investigator. Most of his original work deals with a very theoretic and systema- tic classification of animals, but in his theories he ranges over the whole field of morphology and of embryology, and he partly surveys the domains of palaeontology and of Darwinian anthropology. He was the first to write a history of evolutionary theories. He published a large volume on the beauty of animal forms. He was one of the pioneer students of the Plankton. He wrote on religion and on philosophy. But above everything he was a con- troversialist. He knows no moderation in his attacks on opponents. He combats Church dogmas and upbraids those who reject the theory of evolution and his ideas about embryology or he praises Darwin and his so-called fore- runners, Goethe and Lamarck. But whether he is attack- ing or whether he is praising, there is nowhere any evidence of deep thought, nowhere any suggestion that he has arrived at his convictions after an inward struggle, no- where the slightest attempt at real understanding either of friend or foe. We only see how actively he wields his axe against his foes, and how greatly he overestimates his friends. He compares Darwin with Copernicus! In another place he says that Lamarck is the Copernicus of biology and Darwin its Newton. He says that no one who has a sound judgement and some small knowledge of the subject can help agreeing with his monistic views. With a naivete only equalled by the credulity of his hearers, he asserted that biology had not been a science at all before the time of Darwin ; only then had there begun any 'exact thinking' on biological subjects, only then had 'the almost complete lack of really thoughtful, comparative observa- tion' been remedied. Haeckel believed that the doctrine of evolution was definitely proved, as also that men have descended from monkeys; the occurrence of rudi- mentary organs provides incontrovertible evidence. The theory of Natural Selection he regarded as the most wonderful discovery of the modern intellectual world.

The desire to inspire his reader with an absolutely definite conviction of the truth of his views led Haeckel to love new words, as if every new word represented a new thought! Some few of the words he introduced were accepted, e.g. ontogeny, phylogeny. The great majority were stillborn. When writing his General Morphology Haeckel was still under the influence of idealism : we see this in his postu- late that biology admits of exact mathematical treatment. He was looking for 'the stereometric plan of the organism ; knowledge of this is as important for the organic morpho- logist as is a knowledge of crystallography for the student of inorganic form'. Following in the footsteps of Bronn, he discussed the 'axes' and 'poles' of the organic body ; distinguished between those which have no axis (volvox), those with many axes (regular and irregular), and those with one axis (with equal poles and with unequal poles). He even wrote of 'hemihedric' animal forms, and was con- vinced that all these forms could be explained as resulting from purely mechanical causes.

Afterwards he abandoned these extremely mechanistic views of morphology, and came to disagree with His and Goette, who had tried to explain embryonic development on mechanical principles. Their explanation seemed to him 'too coarse and mechanical', and contradictory to the theory of evolution. For has not every organ a long history ? Has it not reached its present form after uncountable centuries, during which it has undergone innumerable modifications to fit its changing environment, and during which inheritance has continually played its part?

It is useless to seek for an a priori explanation of the fact that Germans inhabit Germany and Frenchmen France. The cause is historical. In the same way, said Haeckel, only in the study of the past can we find the clue to the secrets of animal structure. He declared that phylogeny, the study of the relationship between animals, is not an exact science it is history. The study of evolu- tion is the goal of all human knowledge, the principle underlying all philosophy, the key to every problem, the answer to every question. 'Development is now the magic word by means of which we shall solve the riddles by

which we are surrounded, or at least move along the road towards their solution.' 'Every being can only be truly known when we know his becoming.' Thus morphology, the study of the archi- tecture of the animal body, became 'morphogeny', the study of the evolution of one form from another ; physio- logy became 'physiogeny', a study of the development of function, and of the ontogeny and phylogeny of that function. The evolution of speech, of the upright position, of human culture all these, according to Haeckel, are problems of physiogeny and of physiogeny only. Our study of man must become 'anthropogeny' the study of his origin from animal ancestors.

Regarding evolution, Haeckel formulated certain general laws. The first and most fundamental law of Nature deals with causation. 'According to this highest of all laws, everything that is, has been, or is to be, arises as the necessary result of many contributory causes, and each result becomes in its turn a factor, leading with absolute inevitableness to new results/ Down with ideas of expedi- ency, down with vital force; away with the conception of a world of moral law, with any idea of the freedom of mankind ! The universe is but a great machine, in which the vibrating atoms are the wheels. Here they are massed together to form a glowing sun, there to form a tiny beetle ; here to drive the planets through the universe, there to make man behave like a free and thinking being. There is no fundamental difference between the living and the non-living, for all the elements found in living matter are found in the non-living also, and organic compounds can be artificially produced. Nor is there any fundamental difference in bodily structure, for lifeless crystals have a definite form, just as have some living organisms, while the simplest organisms possess, like flints, no form of their own. The organic and inorganic worlds alike are dominated by two forces, attraction and repulsion between atoms. Molecular motion is the cause of all things even of the soul.

We understand by "soul" and the "soul's activity" a member of excessively complicated reactions of the central nervous system ; the most important are those called "will" and "perception". The will, which lies at the root of all voluntary motion, and perception too, are phenomena which only occur in the well-developed nervous systems of the higher animals: they are complicated molecular movements in the ganglion cells of the central nervous system. 5 Little wonder that Haeckel found such a soul in the one-celled animals, nay, even in plants, for, according to him, plants carry out the same physiological processes as do animals. 'Yes, every atom must have a soul, for it possesses some energy.' Sympathy and anti- pathy, desire and aversion, attraction and repulsion are psychic qualities 'experienced by all atoms'.

Haeckel explains the evolution of organic beings in the following way: Creation by God is unthinkable and contrary to all experience. Nothing then remains but for us to believe in the spontaneous generation of the simplest forms of life, and that out of these all the others have arisen in the course of evolution and at the call of Natural Selection. At first, from lifeless matter there crystallized out non- nucleated cells monads and every animal type now existing had some sort of monad for its original ancestor. From one type came the vertebrates, from another the coelenterata, from yet another the diatoms; one mole- cule more or less of carbon, sulphur, or phosphorus was the only difference between the first forms of life on this earth. But eventually the earth became green with plants, and then followed the animals.

Haeckel turned all work which was inspired by Darwin- ism into new channels. Darwin's method of proof appeared rather strange to the continental scientists of his time. They studied morphology, embryology, palaeontology, classification, the cell theory. Darwin laid emphasis on Natural Selection, on the Struggle for existence', on inheritance, variation, and the details of geographic dis- tribution. He supported his assumptions by facts drawn from the records of animal breeders and from annals of gardening. He discussed the ancestry of pigeons, rabbits, and dogs, made experiments on the resistance of seeds to fresh and salt water respectively, and collected evidence from books of travel and similar somewhat inexact sources. Darwin hardly touched biology as biology was understood on the Continent. In the 400 pages of the Origin of Species he devotes four and a half to morphology and ten to embryology, while the cell theory is hardly mentioned.

Haeckel, on the other hand, did not study variability, hybridization, racial problems, the facts of distribution, of heredity, or any allied subject. He thought that the whole problem could be summed up in the two words Adaptation and Inheritance. Adaptation leads to the creation of new types, while inheritance leads to their fixation. Thus Haeckel included under these two headings the whole of Darwin's book, save a single chapter. This chapter deals with 'Mutual Affinities of Organic Beings ; Morphology, Embryology, Rudimentary Organs'. Haeckel made this chapter the point of departure for his own in- vestigations, and so, at the end of last century, gave a new direction to the whole of biological research. This new school did not attempt to examine Darwin's premises; but classification, morphology, and embryology were directed into evolutionary channels. It was thus that Haeckel arrived at his own concrete theories, at his teach- ing about phylogeny, at the 'Monera', at his 'Fundamental Law of Biogenesis', at the 'Gastrea' theory,

From the eighteenth century onwards it had been believed that the quintessence of an organism is revealed by its form and structure* This idea was held by Linnaeus, Cuvier, de Jussieu, de Candolle, Geoffroy, Goethe, and all the idealists. There were, it is true, some philosophers whose explanations were developed along other lines. Lamarck believed that life reveals itself, not so much in bodily structure as in its strivings, its desires, its contact with the environment, and so on. Oken attempted a physiological classification of animals, but neither his work nor Lamarck's was generally accepted.