Sexual Selection 437 



portion of the phenomena, which he endeavours to explain by the 

 direct action of sexual selection, can only be so explained on the 

 hypothesis that the immediate agency is female choice or preference. 

 It is to this that he imputes the origin of all secondary sexual 

 characters other than weapons of offence and defence.... In this ex- 

 tension of sexual selection to include the action of female choice or 

 preference, and in the attempt to give to that choice such wide- 

 reaching effects, I am unable to follow him more than a very little 

 way." 



Into the details of Mr Wallace's criticisms it is impossible to 

 enter here. We cannot discuss either the mode of origin of the 

 variations in structure which have rendered secondary sexual 

 characters possible or the modes of selection other than sexual 

 which have rendered them, within narrow limits, specifically con- 

 stant. Mendelism and mutation theories may have something to say 

 on the subject when these theories have been more fully correlated 

 with the basal principles of selection. It is noteworthy that 

 Mr Wallace says 1 : "Besides the acquisition of weapons by the 

 male for the purpose of fighting with other males, there are some 

 other sexual characters which may have been produced by natural 

 selection. Such are the various sounds and odours which are 

 peculiar to the male, and which serve as a call to the female or 

 as an indication of his presence. These are evidently a valuable 

 addition to the means of recognition of the two sexes, and are a 

 further indication that the pairing season has arrived ; and the 

 production, intensification, and differentiation of these sounds and 

 odours are clearly within the power of natural selection. The same 

 remark will apply to the peculiar calls of birds, and even to the 

 singing of the males." Why the same remark should not apply to 

 their colours and adornments is not obvious. What is obvious is 

 that "means of recognition" and "indication that the pairing season 

 has arrived " are dependent on the perceptive powers of the female 

 who recognises and for whom the indication has meaning. The 

 hypothesis of female preference, stripped of the aesthetic surplusage 

 which is psychologically both unnecessary and unproven, is really 

 only different in degree from that which Mr Wallace admits in 

 principle when he says that it is probable that the female is pleased 

 or excited by the display. 



Let us for our present purpose leave on one side and regard as 

 sub judice the question whether the specific details of secondary 

 sexual characters are the outcome of female choice. For us the 

 question is whether certain psychological accompaniments of the 

 pairing situation have influenced the course of evolution and whether 



1 Darwinism, pp. 283, 284. 



