160 DARWINISM AND THE PROBLEMS OF LIFE 



this peculiar instinct may be that, in the first place, the 

 animal, which is well adapted to the bark of the tree, 

 protects itself and its eggs best by remaining still ; and, 

 secondly, that the body is too much burdened with 

 eggs to be able to fly. If it is better for the animal not 

 to fly, this instinct suffices to prevent it, and natural 

 selection has no occasion to reduce the wings, as has 

 been done with some of the silk-worms, such as the 

 orgyia, the wings of which have shrunk into small 

 relics. But if the disuse of flight depends only on the 

 overloading of the body with eggs, we do not very well 

 understand the reduction of the wings at first sight. 

 Can it be useful for the butterfly to have the nourish- 

 ment that usually goes to the wings diverted to the 

 rest of the body and the eggs ? When we remember 

 the enormous multiplication of the black arches which 

 still have wings of the full size, we shall not attach much 

 value to this economy of food. Nor can we quite 

 admit, in the case of the whale, that those individuals 

 always had an advantage whose hind-limbs were a trifle 

 shorter than those of their comrades, and so required 

 slightly less food. In view of the enormous mass of 

 muscle and fat in the colossus, this slight economy 

 could never become a matter of life and death, even if 

 it is useful at all to the other organs. 



But, we may further ask, is natural selection bound 

 actively to reduce an organ that has fallen into disuse ? 

 Do we not know that such an organ must deteriorate 

 when selection ceases to affect it ? Every organ only 

 advances from the fact that the individuals that have it 

 in a poorer form are destroyed. When it becomes a 



