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 bea 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 
