The evolution of man and his mind.

Abstract

Speculations in regard to the Origin of Man are always interesting on account of the personal equation. We all like to know as much as we can about the line of one's own ancestry. These theories are of increasing importance because with the spread of education man's conduct is becoming more and more influenced by his thought. Democratic public opinion decides the line of action of the nation, and things learnt in youth constitute one factor at least in the moulding of public opinion. There can be little doubt that the general popular acceptance of the crude struggle for existence was one thought which went far towards unifying German policy before the war. And this simple faith we are now told is not warranted by the facts of science. The current doctrine, extinction of the less fit, and survival of the fittest, no longer commands the universal assent of zoologists. Indeed it has been seriously undermined by the discoveries of recent years. (1) In other words, while the continuity of the protoplasm and the advance of the type has been preserved, the means by which this has been brought about are probably more complex than the simple factors put forward by Darwin and Wallace. In regard to the special case of the evolution of man, my object is to show that recent advances in knowledge have introduced new difficulties both on the side of structure and of function, and have made untenable the current theory of the comparatively recent separation of the human and the ape stocks. I shall then try to picture the forces and environment which seem to be the most probable causes of the evolution of progressive man. Difficulties of the current theory 1. Taking two examples of structure, the premaxilla and the foot, there is no doubt that the problem of the premaxilla is one of the most difficult points in any theory of the descent of man, and its significance is probably commensurate with its difficulty. The following are the salient facts. Man differs from all the other mammalia in the fact that the upper incisor teeth are carried by the maxilla instead of by a separate bone named the inter- or premaxilla, lying below or in front of the nose. This bone is well marked as a separate entity in all the lemurs, monkeys, and apes. In the chimpanzee and orang it unites with the maxilla sooner or later in the adult life of these apes, and the suture between the bones is obliterated. On the bony surface of the human palate a line is usually to be found which was formerly taken as indicating a margin of the premaxilla, but some authorities now consider it doubtful if this line has any such significance. At all events one of the earliest centres of ossification in the foetus appears at the sixth week in the maxilla near the site of the future canine teeth, and from this the portion of the bone which will carry the incisor teeth is laid down during the following month apparently by direct extension from this original centre. The details of the formation of this part of the skull have perhaps not yet been completely worked out, but it seems certain that all traces of the premaxilla--if such ever existed apart from the maxilla--are very speedily lost. So absolutely unique is this disappearance of the bone, that it makes the human embryo distinguishable from that of all other animals at a time when the foot has the shape of the generalised reptilian type; the five digits are arranged like a fan and equally spaced apart, and the cartilage of the little toe is quite as large as that of the great toe. (2) But according to the recapitulation theory, that the embryological life of the individual gives a summary of his ancestry, the disappearance of the premaxilla so very early in faetal life would indicate (a) that the pre-human stock had lost the bone, and therefore had already separated from the apes at an immensely distant epoch; or (b) that man has been able in recent times to get rid of inherited structures which he did not require; or (c) that the common ancestor had a small premaxilla which has become proportionately more prominent in the apes and less so in man since the separation of the two stocks. …