THE SEXES AND SEXUAL SELECTION. 1 3 



tion." The males are the more variable, but more than that, 

 their variations are much more likely to be transmitted. " We 

 are thus able to understand the great difference in the males 

 of allied species, the difference between the adult male and the 

 female or young, and the great diversity and variability of 

 secondary male characters; and we should expect to find, what 

 actually is the case, that among the higher animals, when the 

 sexes have long been separated, the males are more variable 

 than the females." The contrast between Darwin and Brooks 

 may now be summed up again in a sentence. Darwin says, 

 the males are more diversified and richer in secondary sexual 

 characters, chiefly because of the sexual selection exercised 

 alike in courtship and in battle. Brooks admits sexual 

 selection, but finds an explanation of the greater diversity of 

 the males in his theory that it is the pecuhar function of the 

 male elements to transmit variations, as opposed to the constant 

 tradition of structure kept up by the egg-cells or ova. In 

 other words, the females may choose, yet the males lead ; nay 

 more, they must lead, for male variations have by hypothesis 

 most likelihood of being transmitted. 



Full consideration of this hypothesis would involve much 

 discussion of the problems of inheritance, which will form the 

 subject of a forthcoming volume ; but the general conclusion 

 of the naturally greater variability of the males, will be stated in 

 a different light towards the close of the following chapter. It 

 will there be shown that the "something within the animal," 

 which determines the preponderance of male variability, may 

 be stated in simpler terms than are involved in Brooks's theory 

 of heredity. To refer preponderant male variability back to a 

 power, ascribed to the male reproductive cells, of collecting and 

 storing up assumed gemmules, is at best but a half-way analysis. 



Both the above critics are at one with Darwin on essential 

 points. Though Wallace would explain by natural selection 

 what Darwin explained by sexual selection, he does not deny 

 the importance of the latter in many cases. Brooks, again, 

 emphasises a deeper factor, without doubting the general truth 

 of Darwin's account of the process. Different from both 

 these positions is that {c) occupied by St George Mivart, who 

 looks for some deeper reason than either Darwin or Wallace 

 suggest. The entire theory of sexual selection appears to him 

 an unverified hypothesis, only acquiring plausibility when sup- 

 ported by quite a series of subsidiary suppositions. He submits 



