The History of Biological Theories

Thi book should be returned on or before the date last marked below. MY thanks are due to Professor Julian Huxley, who first suggested that Dr. Radl's work should be made available to English readers, and to Dr. Charles Singer for his expert help and advice in the work of translation. IT gives great pleasure to write a book, but the author's greatest joy comes when his labours are ended, and he feels himself free to devote his attention to other things.

When I had completed this book, I found myself in that happy position; and not even the news that the whole edition had been solfl provided an impetus great enough to drive me to take up the task again. For revision became necessary. The book is a history, and history does not stand still. It develops unintermit- tently, bringing forth new ideas and continually throwing fresh light on the past. The demand for an English version encouraged me to a renewed effort, and, at the request of the English pub- lishers, I set to work once more, abridging in places, in others making such alterations and additions as seemed absolutely essential to make the present situation clear.

I will not attempt to indicate what I have retained of the 1909 German edition, or what I have omitted. I will rather attempt to summarize, very briefly, the most out- standing changes which have occurred in the position of the sciences since the German edition of the book was published; such changes as are important for a true appreciation of the views here put forward. That decline of interest in the Darwinian theory which was discussed in the German version, has steadily con- tinued. To the theory that living organisms have de- veloped, the more complex from the more simple, through countless eons of time, and that man has been evolved from an animal ancestor to this theory of evolution no weighty objection has been raised.

It is true that the theory has not received any clinching scientific proof. But it is, on so many lines of evidence, so extremely probable, and the objections to it are so slight, that we may, for all practical purposes, safely assume that it is true. But, in the nineteenth century, the enthusiasm for the theory was so great that its upholders expected it to lead to a revolution of our whole civilization ; of our social institutions, our politics, and our science; even of our philosophy and our religion.

This revolutionary tendency of the theory has dis- appeared. Biology itself is no longer as interesting as once it was to the man in the street. It is no longer the leading science in the life of civilized man. Its place is being usurped by theoretical physics, and, at the present moment, by chemistry. Einstein has now placed himself upon the throne formerly occupied by Darwin. We may indeed question whether Natural Science is the leading discipline in the intellectual life of to-day. It is still the predominating interest of the Anglo-Saxon peoples, though, even with them, the focus of interest tends to be the technical applications of the sciences, rather than the pure sciences themselves.

In Europe, however, and especially in Germany, there is a very general and growing conviction that the nine- teenth century over-estimated the importance of Natural Science in the life of the people. The sciences, it is felt, were stressed at the cost of the more purely intellectual subjects. Hence to-day it is the fashion to attach more importance to history, especially philosophical history, to jurisprudence and the more theoretical aspects of sociology.

In view of all these modern movements, should we not ask ourselves whether there is any obvious reason for the condition of stagnation into which some aspects of bio- logical investigation have fallen. Since about 1890 practi- cally no advance has been made in our knowledge of the origin of living organisms. Can this, by any chance, be due to the fact that our methods have been too exclusively the methods of science ? It would be quite possible to

treat the past history of the world of living organisms as an historical problem, and to attempt to solve the problem by historical methods. It would then be analogous to the study of the origin of religions or of the various European States. The more I, personally, think on the subject, the more I believe in this method of attack. We should have to revise our whole methodology and to adapt it to this new conception of the problem. Above all, we should have almost completely to abandon that positivist attitude which characterized the work of the second half of the nineteenth century. This would involve a thorough investigation of Driesch's work on the auto- nomy of the life processes. Such a study would lead us to realize how analogous are the physical activities of living organisms to mental activities. We should then be pre- pared to attack the history of the physical as we now study the history of literature, of civilization, or of philosophy.

Let me give a concrete example which will make my meaning clear. We have, so far, always attempted to visualize the physical processes by which man, regarded as a physical structure, was gradually evolved from some lower organism. The historian might do just this. He might give us the detailed ancestry of an Alexander the Great, a Caesar, a Locke, Dante, or Napoleon, and hold that he had fulfilled his function as an historian by making such an ancestral portrait gallery more complete. But this is not the method of the historian. He describes his heroes as the originators, the protagonists or antagonists of ideas which have domi- nated mankind. He speaks of the development of the imperial idea, of empiricism, of the poetry of Dante.

The world of living organisms seems likewise to be dominated by ideas, and it would surely be worth our while to study these more closely, and, by such a study, to endeavour to throw fresh light on the past. This is, however, merely a suggestion for the future. To-day the biological sciences are facing a time of crisis a crisis even more acute now than it was twenty years ago, when I first approached these problems in the German edition of this work.

To conclude. It was a very great age, that second half of the nineteenth century which saw the birth of the evolutionary theory. This book was written to show my readers how tremendously important the conceptions then formulated were. The question of the origin of species had to be raised it was essential for man's intellectual progress. The Darwinian theory represents a very great step forward but it was a step forward, not the end of the march. Our goal lies still further ahead, and to march ever onwards should be the task of the generation now living.

Page 1 80, line 6, for Fleischman read Fleischmann Page 217, line 23, for Ettinghausen read Ettingshausen Page 308, line 5, for Leibniz read Leibnitz Page 329, line 26, for Mallpas read Maupas Some Earlier Views Concerning the Origin of Animal Forms . i The Views of Darwin and the Darwinists .... 93 The Attitude of the Church 95 The Controversy about the Idea of Types . . . .186 Embryology in the Darwinian Period 190 Humboldt classifies Plants according to their Habitats . . 197 Darwin's Historical and Experimental Conceptions applied to

Wallace's Zoological Regions and their Botanical Equivalents . 202 A Return to the Study of the Direct Dependence of the Flora Variability regarded as the Result of the Influence of Environ- ment on the Organism 320 Science and the Presentation of its History .... 395 The Recognition of Ideas 396 I . Some Earlier Views Concerning the Origin of Animal Forms. IN his Autobiography ', Charles Darwin writes that his contemporaries attempted to account for the success of his theory by suggesting that men's minds were pre- pared for it, but, so he tells 'us, this was not, in fact, the case. He relates that, during the composition of his book, he often discussed the subject of development with other naturalists, but never 'happened to come across a single one who seemed to doubt the permanence of species'. It is easy to believe this, but we may question whether this method of cross-examining friends was very suitable for estimating the contemporary trend of thought. Obvi- ously it could not be exhaustive.

Speculations on the origin of the world are, indeed, as old as man himself. Haeckel rightly claimed Moses as a forerunner of Darwin. The Vedic Poems, which are of immense antiquity, ask 'What was the wood, what the tree from which the framework of Heaven and Earth was formed ? ' The myths of the egg from which the earth arose, of the origin of the Universe from water or from fire, of the creation of the first men, gave early answers to Darwin's question concerning the origin of species.

Studying the first sentences of the Bible, the Christian Fathers propounded many theories as to the commence- ment of the world. While St. Clement, St. Origen, and St. Athanasius tried to prove that all forms of organisms were produced simultaneously by one creative act, the school of Cappadocia, with St. Basil at its head, taught that God originally created only 'elements', which reached their final purpose by a process of development, St. Gregory of Nyssa and St. Augustine expressed this same idea even more clearly. The very dreams of the early Christians

themselves their pictures of a lost or of a future Paradise, of the Millenium, of the end of the world are but ex- pressions of the view that things to-day are not as they once were, nor as they will yet be. These thoughts, however, expressed a philosophy, a pious belief, a desire born of fear, rather than knowledge based on actual facts. Only in more recent times, and particularly since the eighteenth century, have we come clearly to recognize that Man and Nature have a history. For this view Rousseau prepared the way by his teaching that the natural man is the happy man, and that civiliza- tion has a pernicious influence.

In Great Britain the eccentric Scot, James Burnett, Lord Monboddo (1714-99), put forward theories as to the origin of speech, and the development of men from monkeys. Herder was then writing on racial evolution, and seeking to turn history into natural history. Kant, and not long after him, Laplace, formulated the well- known Nebular Hypothesis, suggesting that the Solar System came originally into being according to mechanical laws and as the result of a process of condensation of gases. At the end of the century Cuvier set forth his account of the history of the earth's crust and its living inhabitants.

German natural philosophy was full of similar thoughts. Goethe wrote so much about evolution that Haeckel claims him as a forerunner of Darwin. Although Fichte was much less historically minded, his theory that 'being* is the result of 'doing', that the ego is formed by a world external to it by the non-ego constitutes something in the nature of a metaphysical embryology of nature. In Schelling we hear echoes of the old doctrine of the natura naturans ; we still have, that is, a dynamic view. Evolu- tionary ideas formed the pivot of Hegel's philosophy. He looked on the world as a manifestation of developing intelli- gence, beginning with a logical idea and passing through unconscious nature to self-conscious man, and ultimately to social organization, to knowledge, art, and religion.

Hegel's influence upon historic thought in Germany, France, Russia, and elsewhere, is fully recognized. Nevertheless, these evolutionary views of the earlier nineteenth century differed greatly from the modern ones. Darwin sought to make his presentation historical. It is based on the thought that the history of the world is full of events; that every transformation of one organism into another presents the world with a new fact ; and that there have been an infinite number of such facts. Goethe, Fichte, Schelling, Oken, Hegel, Braun, von Baer all these thinkers paid attention to the events by which evolution proceeds, merely to deduce there- from a law of development, an idea. A change from the older idealistic to the newer realistic conception pre- sented no great difficulty. This is made very clear by the works of Strauss and Feuerbach, Hegel's pupils, in whose hands the idealistic teaching of their master became pure materialism.

Moreover, evolutionary ideas were not absent from pre- Darwinian technical biology. It is true that the views of Lamarck were not generally accepted, but his writings were read, apparently with ever-increasing interest. The fate of his theory in France is well known. In England Lyell (1830) referred to him in his Geology, and doubtless directed the attention of many readers to Lamarckism, for while speaking of the Lamarckian theory as a 'phantastic romance', he admired the assiduity of Lamarck's defence of a forlorn hope. Von Baer says that, in the Germany of his day, almost all the older scientists had read Lamarck's Pbilosopbie Zoologique.

The Morphologists were at that time occupied in arrang- ing living organisms in series of ever-increasing com- plexity. Beginning with the simplest, they passed by gradations to the most highly developed forms. They were steeped in the belief in Nature's creative force, and they spoke of the 'Progress' and the 'Perfecting' of these forms. To most these were but abstract ideas, yet there were some who understood by 'progress' a perfection which required

long periods for its attainment ; some even occupied them- selves in constructing what were, in effect, genealogical trees of animal descent. A certain Kaup, for example, gave the following stages in development: Dolphin Seal Sloth Elephant. Tortoise Horse Rhinoceros. Lizard Black-cock Stag. How vital was the interest in this question can be seen from the fact that the University of Munich, in 1834, offered a prize for a thesis on 'The Causes of the Mutability of Species'.

The decline of formal morphology gave a new impetus to the genetic point of view. Scientists became more and more aware that an organism is by no means a 'torpid crystal', but that, standing in living inter-relationship with its environment, it is ever in a state of change. The interest in morphology was replaced by an interest in embryology, which gave a truer picture of life, in that it endeavoured to portray the origin, development, and death of the individual body. Von Baer the embryologist was then one of the moderns.

We can follow these changes in point of view if we consider the various current ideas as to the vertebral origin of the skull. Goethe (1790) was the first to express the view that it is formed on the same plan as the backbone. In the early nineteenth century this idea was much in favour and was expressed in various ways. Some thought of the skull as a single modified vertebra. Goethe had at first assumed that three, and later that six vertebrae went to its formation. Oken expressed a similar thought in more extreme form, considering 'the whole Man a vertebra'. Geoffroy extended the conception farther, and regarded the insect body likewise as composed of vertebrae, assumed to be external, the organs beiag internal. Others, for example Carus, professed even more fantastic views. All were variations on the theme that the vertebra is repeated in numerous parts of the body.

In considering these bizarre views of the older morpho- logists we should remember that they did not visualize a concrete vertebra as repeated in every part, but a generalized recurring vertebral plan. As Goethe expressed it 'Identical parts undergo manifold transformations under the action of a vital force.' The theory of the vertebral origin of the skull was supported in England by Owen and challenged by T. H. Huxley, one of the younger anatomists full of von Baer's developmental views. Huxley objected to it on embryological grounds. He held that although in the earlier stages of development the skull is segmented, as is also the rudiment of the backbone, yet from these similar beginnings skull and vertebral column develop along wholly different lines.

Yet Huxley's view, opposed as it was to the forms of the theory expressed by Oken, Carus, Owen, and others, was in no sense a contradiction of that of Goethe, but rather a modern version of the same thought. Nevertheless the expression adopted by Huxley shows clearly the change in point of view with the advance of time. Belief in a fore- ordained plan had been replaced by belief in development. This was, for the moment, only embryonic development. Soon, however, the word took on a wider meaning and came to signify an historical development.

With this renewed interest in embryology, palaeontology, the true science of the history of creation, also increased in prestige. To Cuvier palaeontology was a department of geology. Blainville already placed it near zoology, including living and extinct animals in one series; we probably see here the influence of Lamarck. Palaeonto- logical knowledge quickly increased. About the middle of the century, there began to appear in Germany popular works with such titles as A History of Creation. These paved the way for the diffusion of the evolutionary idea. By 185 1 palaeontology was so much in the vision of natural- ists that Vogt subdivided zoology into (i) palaeontology; (2) morphology of existing animals ; (3) embryology.

There were many distinguished biologists who not only came near to the idea of evolution proceeding in time, but who already recognized that the problems of evolution are the most fundamental in biology. Thus in 1833 von Baer the embryologist lectured on the subject of 'Natural Law in Development'. 'The problem of Creation', said the lecturer, 'is the fundamental problem of biology ; when that is solved, all others become clear. Observation of living things in our own time shows the individual passing away, but the species surviving as the expression of a definite thought. Yet observation based on wider knowledge, especially on palaeontological grounds, leads to the conviction that even the species is not eternal. It appeared at a particular moment in world history, and later disappears again. We do not know how it first arises. Each species must either have arisen through a special act of Creation, or must have arisen from some pre-existing species. A new creation may have taken place many times. But if the species dies out, what is it that continues ? Does not the whole mystery of existence lie hidden in this history of species ? And what is its meaning ? Since the history of Nature is a history of continual advance from the less to the more perfect form, must we not answer "the History of Nature is but the history of the in- creasing victory of the spiritual over the material f" 1 That is the essential idea of Creation.'

This discussion contains the germ of a transcendental evolutionary philosophy, and propounds questions that none can think solved. Many others agreed with von Baer ; Bronn the well-known morphologist and palaeonto- logist, the botanist Braun, the entomologist Burmeister, the French physiologist Milne-Edwards, the German physiologist Johannes Miiller, the biologist Treviranus, and many others. These differed indeed in their solution of the problem, but the fact remains that in the second quarter of the nineteenth century most of the great

1 C. E. v. Baer, 'Das allgemeine Gesetz der Natur in aller Entwicklung', Reden, i, p. 72. biologists were following these evolutionary questions with interest. Moreover, the problem of the origin of man was being seriously discussed in Germany, in the forties, under Herder's far-reaching influence. Max Miiller cites a treatise which, by an act of irony, appeared in 1840 in a theological newspaper ! This treatise set out to show that man has developed from the monkey! Later, when Darwinism held the field, naturalists sought for and found his forerunners in numbers. Blinded by the brilliance of the new theory, they looked upon it as an absolute truth a truth in no way connected with the thought of the time, but the discovery of a genius. The duty of the historical writer was to search history for other geniuses of lesser rank, who had stumbled on this truth that had been completely revealed by Darwin. They did not suffi- ciently analyse Darwin's fundamental ideas. They gave too much consideration to certain minor points in his theory, and so declared those to be the forerunners of Darwin, whose thought had in fact scarcely approached his. In almost every philosophical writer from Empedocles and Aristotle to Goethe, the inquiring eye of faith of some historian would discover a masked Darwin. And yet the idea that there can be 'something new under the sun' had contended vainly for recognition in the eighteenth century, not to speak of earlier times !