The Last Link/Introductory

At the end of the nineteenth century, the age of 'natural science,' the department of knowledge that has made most progress is zoology. From zoology has arisen the study of transformism, which now dominates the whole of biology. Lamarck^[1] laid its foundation in 1809, and forty years ago Charles Darwin obtained for it a recognition which is now universal. It is not my task to repeat the well-known principles of Darwinism. I am not concerned to explain the scientific value of the whole theory of descent. The whole of our biological study is pervaded by it. No general problem in zoology and ​botany, in anatomy and physiology, can be discussed without the question arising, How has this problem originated? What are the real causes of its development?

This question was almost unknown seventy years ago, when Charles Darwin, the great reformer of biology, began his academical career at Cambridge as a student of theology. In the same year, 1828, Carl Ernst von Baer^[2] published in Germany his classical work on the embryology of animals, the first successful attempt to elucidate by 'observation and reflection' the mysterious origin of the animal body from the egg, and to explain in every respect the 'history of the growing individuality.' Darwin at that time had no knowledge of this great advance, and he could not divine that forty years later embryology would be one of the strongest supports of his own life's work—of that very theory of transformism which, founded by Lamarck in the year of Darwin's birth, ​was accepted with enthusiasm by Charles's grandfather Erasmus. There is no doubt that of all the celebrated naturalists of the nineteenth century Darwin achieved the greatest success, and we should be justified in designating the last forty years as the Age of Darwin.

In searching for the causes of this unexampled success, we must clearly separate three sets of considerations: first, the comprehensive reform of Lamarck's transformism, and its firm establishment by the many arguments drawn from modern biology; secondly, the construction of the new theory of selection, as established by Darwin, and independently by Alfred Wallace (a theory called Darwinism in the proper sense); thirdly, the deduction of anthropogeny, that most important conclusion of the theory of descent, the value of which far surpasses all the other truths in evolution.

It is the third point of Darwin's theory that I shall discuss here; and I shall discuss ​it chiefly with the intention of examining critically the evidence and the different conclusions which at present represent our scientific knowledge of the descent of man and of the different stages of his animal pedigree.

It is now generally admitted that this problem is the most important of all biological questions. Huxley was right when in 1863 he called it the question of questions for mankind. The problem which underlies all others, and is more deeply interesting than any other, is as to the place which man occupies in nature and his relations to the universe of things. 'Whence our race has come; what are the limits of our power over nature, and of nature's power over us; to what goal are we tending—these are the problems which present themselves anew and with undiminished interest to every man born into the world.' This impressive view was explained by Huxley thirty-five years ago in his three celebrated essays on 'Evidence ​as to Man's Place in Nature.' The first is entitled 'On the Natural History of the Man-like Apes'; the second, 'On the Relations of Man to the Lower Animals'; the third, 'On some Fossil Remains of Man.' Darwin himself felt the burden of these problems as much as Huxley; but in his chief work, 'On the Origin of Species,' in 1859, he had purposely only just touched them, suggesting that the theory of descent would shed light upon the origin of man and his history. Twelve years later, in his celebrated work on 'The Descent of Man, and Selection in Relation to Sex,' Darwin discussed fully and ingeniously all the different sides of this 'question of questions' from the morphological, historical, physiological, and psychological points of view. As early as 1866 I myself had applied in the Generelle Morphologie der Organismen the theory of transformism to anthropology, and had shown that the fundamental law of biogeny claims the same value for man as for all the other animals. The intimate causal ​connection between ontogeny and phylogeny, between the development of the individual and the history of its ancestors, enables us to gain a safe and certain knowledge of our ancestral series. I had at that time distinguished in this series ten chief degrees of vertebrate organization. I attributed the highest importance to the logical connection of anthropogeny with transformism. If the latter be true, the truth of the former is absolute. 'Our theory that man is descended from lower vertebrates, and immediately from apes or primates, is a case of special deduction which follows with absolute certainty from the general induction of the theory of descent.' The full proof and detailed explanation of this view was afterwards given in my 'History of Natural Creation,' and especially in my 'Anthropogeny.'^[3] Lastly, it has received an ample scientific and critical foundation in the third part of my 'Systematic Phylogeny.'^[3]

​During the forty years which have elapsed since Darwin's first publication of his theories an enormous literature, discussing the general problems of transformism as well as its special application to man, has been published. In spite of the wide divergence of the different views, all agree in one main point: the natural development of man cannot be separated from general transformism. There are only two possibilities. Either all the various species of animals and plants have been created independently by supernatural forces (and in this case the creation of man also is a miracle); or the species have been produced in a natural way by transmutation, by adaptation and progressive heredity (and in this case man also is descended from other vertebrates, and immediately from a series of primates). We are absolutely convinced that only the latter theory is fully scientific. To prove its truth, we have to examine critically the strength of the different arguments claimed for it.