x COLOURS AND ORNAMENTS CHARACTERISTIC OF SEX 283 
the pupa, and among migrating birds the males arrive first 
both in this country and in North America. The struggle 
is thus intensified, and the most vigorous males are the 
first to have offspring. This in all probability is a great 
advantage, as the early breeders have the start in securing 
food, and the young are strong enough to protect themselves 
while the later broods are being produced. 
It is to this form of male rivalry that Mr. Danvin first 
applied the term “sexual selection.” It is evidently a real 
power in nature; and to it we must impute the development of 
the exceptional strength, size, and activity of the male, together 
with the possession of special offensive and defensive weapons, 
and of all other characters which arise from the development 
of these or are correlated with them. But he has extended 
the principle into a totally different field of action, which 
has none of that character of constancy and of inevitable 
result that attaches to natural selection, including male 
rivalry; for by far the larger portion of the phenomena, 
which lie 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, 
of all the ornamental crests and accessory plumes of birds, 
the stridulating sounds of insects, the crests and beards 
of monkeys and other mammals, and the brilliant colours and 
patterns of male birds and butterflies. He even goes further, 
and imputes to it a large portion of the brilliant colour that 
occurs in both sexes, on the principle that variations occurring 
in one sex are sometimes transmitted to the same sex only, 
sometimes to both, owing to peculiarities in the laws of inherit¬ 
ance. In this extension 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 ; and I will now 
state some of the reasons why I think his views are unsound. 
Sexual Characters due to Natural Selection. 
Besides the acquisition of weapons by the male for the 
purpose of fighting with other males, there are some other 
