332 THE SIGNIFICANCE OF SEXUAL REPRODUCTION, ETC. 



of the same species ; most easily of all the differences observable 

 in this respect between the germ-cells of different species. 



Of course, this hereditary power is always relative, as may be 

 easily proved by cross-breeding between different species and races. 

 Thus when a fantail pigeon is crossed with a laugher, the characters 

 of the former preponderate, but when crossed with a pouter the 

 characters of the latter preponderate 1 . The facts afforded by cross- 

 breeding between hybrids and one of the pure parent species, 

 together with a consideration of the resulting degree of variability, 

 seem to me to be even more unfavourable to Brooks' view. They 

 appear to me to admit of an interpretation different from that 

 brought forward by him ; and when he proceeds to make use of 

 secondary sexual characters for the purpose of his theory, I believe 

 that his interpretation of the facts can be easily controverted. It 

 is hardly possible to conclude that variability is due to the male 

 parent, because the males in many species of animals are more 

 variable, or deviate further from the original type, than the females. 

 It is certainly true that in many species the male sex has taken 

 the lead in processes of transformation, while the female sex has 

 followed, but there is no difficulty in finding a better explanation 

 of the fact than that afforded by the assumption ' that something 

 within the animal compels the male to lead and the female to follow 

 in the evolution of new breeds.' Brooks has with great ingenuity 

 brought forward certain instances which cannot be explained with 

 perfect confidence by Darwin's theory of sexual selection, but this 

 hardly justifies us in considering the theory to be generally in- 

 sufficient, and in having recourse to a theory of heredity which is 

 as complicated as it is improbable. The whole idea of the passage 

 of gemmules from the modified parts of the body into the germ- 

 cells is based upon the unproved assumption that acquired characters 

 can be transmitted. The idea that the male germ-cell plays a 

 different part from that of the female, in the construction of the 

 embryo, seems to me to be untenable, especially because it conflicts 

 with the simple observation that upon the whole human children 

 inherit quite as much from the father as from the mother. 



1 Darwin, ' Variation of Animals and Plants under Domestication,' 1875, "Vol. H- 

 p. 41. 



