needs no further elucidation here as the principal factor in the evolution in man, first of the family relation, then of the clan, the tribe, and the nation. With this factor in mind, and the immense superiority which anthropoid man must have had, when brain development had once induced this fundamental community of interest over the rest of brute creation, the gap between primitive man and the higher anthropoid apes in the past, or between the present lower races of man and the higher existing primates, is easily explained, even if it had not been greatly exaggerated. At the present time we may note and record the further inevitable increase in the gap, for the lower races of man are gradually becoming extinct, and the higher apes can not long hold their own or persist.
Brooks's Hypothesis.—I have already alluded to Brooks's hypothesis under the head of sexual differentiation, and his work on heredity must be so familiar to you that his views need but a passing notice. He believes that sex differentiation means fundamentally a physiological division of labor, and that the male is essentially the progressive or diversifying and the female the conservative agent. As organisms gradually increased in size, as the number of cells in their bodies became greater, and as the differentiation and specialization of these cells became more and more marked, one element, the male cell, became adapted for storing up gemmules, and, at the same time, gradually lost its unnecessary and useless power to transmit hereditary characteristics.
The theory finds support in some of the phenomena of life, and doubtless expresses a law not easily established, for which reason it will not be readily accepted. It leaves entirely out of consideration some of the forces at work which I have already indicated, and in so far must be considered only a law of secondary importance. However much we may admit the general truth that the germ-cell continues the past and the sperm-cell tends to diverge from it, as a purely dynamic proposition, inducing variation for natural selection to play upon, it does not in any way decrease the overwhelming importance of the female in inducing, through psychico-physiological influences, a needed and purposeful modification in the manner which I have already expounded.