64 THE THEORY OF NATURAL SELECTION 



exaggerated appendages on account of the loss of 

 activity which they must entail. We are, therefore, 

 obliged to conclude that natural selection is much less 

 rigorous in its action than some people have supposed, 

 for if this principle is inadequate to prevent such an 

 exuberance of form and colour in these particular 

 instances, its action becomes open to question in 

 other cases as well. 



Similarly, Morgan finds a difficulty in understanding 

 why natural selection has not led to the extermination 

 of species which are handicapped by the existence of 

 internecine strife between the males, in favour of other 

 species which faced the battle of life with united 

 strength. But in this argument it seems to be for- 

 gotten that examples of the kind of strife in question 

 are most frequent among herbivorous animals, where 

 the struggle for existence must be chiefly determined 

 by the quantity of vegetable food which the individuals 

 can obtain, so that the loss of the weaker males may 

 not be a disadvantage. Moreover, Darwin's conclusion 

 that natural selection is most rigorous between members 

 of the same species is left out of account. 



The preceding arguments seem to show that in par- 

 ticular cases certain structures and phenomena asso- 

 ciated with species cannot be explained as having 

 arisen through the unaided action of natural selection. 

 When weighed against the great mass of evidence 

 which Darwin accumulated in support of his theory, 

 these few considerations cannot be said to be in any 

 way fatal to the belief that natural selection of minute 

 differences has played an important part in the origin 



