200 THE FUNCTION OF SEX 



ourselves to be blinded by that veil of familiarity which is so apt 

 to obscure the significance of common facts. To me it seems 

 likely that the failure to discover the function of sex is due 

 largely to the circumstance that the attention of biologists has 

 been concentrated, on the one hand, on progressive evolution, and 

 on the other hand, on striking abnormalities. Retrogressive 

 evolution, which is every wit as important, every wit as adaptive 

 as progressive evolution, has received scant attention ; and 

 biologists, with hardly a recent exception, have attributed it to 

 the same agency (direct selection) as produces progression. The 

 fact that it occurs in the total absence of direct selection has not 

 received due weight. Presumably, sex has some function. The 

 two theories most in favour with biologists at preseut are, on the one 

 hand, the hypothesis that it renders species variable and so 

 provides materials for Natural Selection, and on the other, that it 

 mixes parental qualities as marbles are mixed. We have already 

 dealt with the Mendelian hypothesis. No one not a Mendelian 

 doubts the swamping effect of sex on progressive variations. The 

 function of sex, therefore, cannot be the provision of progressive 

 variations as materials for the work of Natural Selection. Sex itself 

 must have been evolved by the prolonged selection of pre-existing 

 progressive variations. 1 Moreover, it has been proved that par- 

 thenogenetic species display such variations in plenty. Indeed, a 

 principal part of the work of Natural Selection seems to be to 

 confine variations within useful bounds. 



328. Before we can be in position to understand the effect and 

 the function of conjugation, we must study normal intra-varietal 

 breeding. We are quite incapable of observing its effects in plants 

 and lower animals. Even in human beings, with which we are so 

 familiar, our task is rendered very difficult by the constant presence 

 of spontaneous variations arising independently of sex. Modi- 

 fications, due to the action of the environment on the germ-cell 

 as well as on the soma, also complicate matters. However, we 

 have no reason to suppose that amongst human beings, 

 members of a natural ' wild ' species, the effects of conjugation 

 differ greatly, if at all, when the breeding is inter-racial from what 

 it is when it is intra-racial. Many human varieties differ so widely 

 that when they cross we are easily able to note the effect of con- 



1 Possibly it originated in attempted cannibalism amongst unicellular organ- 

 isms, an attempt which resulted in beneficial fusion. Thence, perhaps, during the 

 evolution which adapted species for conjugation, arose gradually those multi- 

 tudinous sexual differentiations which we find in multicellular animals and plants. 



