i66 PROBLEMS OF EVOLUTION 



species there are fights among the males. The peacock, though 

 it might seem to be no better than a lay figure for showing off 

 a costume, is known to fight desperately. Generally speaking, 

 spurs are part of the equipment of the polygamist. It is true 

 that the ruffs (Machetes pugnax) have none, and their sparrings 

 are said not to be fights but only a stately make-believe. But 

 they are also said to be polygamous, and it is difficult to recon- 

 cile these two statements. There is strong reason, it is true, 

 for believing that the hens have preferences, but that this alone 

 should lead to polygamy is hardly conceivable. We are driven 

 to assume that it has its origin in the pugnacity of the cock-birds. 

 It follows, therefore, that, however extravagant their plumage, 

 it is always the concomitant, or rather the expression, of high 

 spirit. 



Mono- As yet I have said little about the species in which pairing 

 Species ' IS t ^ ie ru l e - I n them, too, we often find that the cock is much 

 brighter than the hen, and has a brilliancy of plumage which, 

 it might have been thought, Natural Selection would not have 

 allowed. There is much evidence in support of the view that 

 in most species of birds the cocks greatly outnumber the hens. 

 If this is so, a cock-bird is confronted with one or other of 

 two dangers ; through dulness and the concomitant want of 

 vigour he may remain unmated, or through excess of brilliancy 

 he may meet an untimely death. In those species where the 

 latter danger is the smaller of the two there is likely to be a 

 further evolution of masculine beauty ; where the former counts 

 for little there is likely to be no further embellishment. 



Where the males have no superiority in numbers, still the 

 brighter and more vigorous of them will pair with the more 

 vigorous females, and will leave more numerous and finer off- 

 spring. Thus here too the same system will work well. But 

 Natural Selection will obviously put a greater check upon extra- 

 vagance of ornamentation, since the gain to the species from 

 competition among males is less where the supply does not 

 exceed the demand. The excess is clearly greatest in poly- 

 gamous species, and it is there that we find ornamental plumage 

 most highly developed. The following formula is very probably 



