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!: “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. 
