Charles Darwin and the Theory of Natural Selection

by Sir Edward Bagnall Poulton

The work on “The Descent of Man” was begun as soon as Darwin had sent the manuscript of “Animals and Plants” to the printers, although notes on the subject had been collected from time to time during the previous thirty years—in fact, ever since Darwin had come to definite conclusions on evolution.

The book was published February 24th, 1871, but, as in the case of his other publications, continuous work upon the manuscript had been impossible. The volume attracted great interest, and 5,000 copies were printed in 1871 in addition to the first 2,500.

The full title of the book is “The Descent of Man, and Selection in Relation to Sex,” and, as this title almost implies, it is made up of two distinct works, which might well have been issued separately. The first part, dealing with man, is far shorter than the other. Darwin had from the first considered that his theory of evolution by natural selection would involve man as well as the other animals, and, that no one might accuse him of want of candour, he had said in the “Origin” that by this work “light would be thrown on the origin of man and his history.” But he was anxious to justify this statement, which was, of course, distasteful to very many in those days, by a most complete treatment of the subject.

DESCENT OF MAN.

He opens this part of the work, which he calls “The Descent or Origin of Man,” by discussing the structures which are common to man and animals, including those which are represented in man in a rudimentary state, and by showing the similarity of the phases through which man and animals pass during their embryological development.

Having thus shown that man was probably descended from some lower form, he considers the mode by which the process was effected, showing that man possesses variability in body and mind, and is, like other animals, subject to all the laws of inheritance and variation, and to the direct action of surrounding conditions, and to the effect of the use and disuse of parts, and that his rate of increase is such as to render a large amount of extermination inevitable. In other words, he presents the same facilities for the operation of natural selection as those presented by other animals. The points in which man differs from other animals are then considered in relation to their possible origin by natural selection. The differences and resemblances between the mind of man and animals are discussed in much detail, and the origin of the former through natural selection is defended. This part concludes with the consideration of the position of man in the animal series, his birthplace and antiquity, and with an account of the formation of races.

In the second part Darwin brings forward a large body of evidence in favour of his hypothesis of sexual selection—viz. the view that, in the higher animals, some alteration, especially of the secondary sexual characters, is produced by the preferences and rejections of the sex which is sought by the other. Such results are commonly found in the males as a result of the preferences of the females accumulated through countless generations; but in some species the females court the males, and are themselves subject to the same process of improvement by selection.

Opinion is still divided on this most interesting question. Wallace, more convinced than ever as to the efficiency and scope of natural selection, after first doubting, has finally come to reject sexual selection altogether. Probably the majority of naturalists are convinced by Darwin’s arguments and his great array of facts that the principle of sexual selection is real, and accounts for certain relatively unimportant features in the higher animals, and they further accept Darwin’s opinion that its action has always been entirely subordinate to natural selection.

A brief third part considers sexual selection in relation to man.

Darwin says, in his “Autobiography,” that sexual selection and “the variation of our domestic productions, together with the causes and laws of variation, inheritance, and the intercrossing of plants, are the sole subjects which I have been able to write about in full, so as to use all the materials which I have collected.”