110 THE ORIGIN OF SPECIES 



or that variety shall survive. But when man is the selecting agent, 

 we clearly see that the two elements of change are distinct; 

 variability is in some manner excited, but it is the will of man 

 which accumulates the variations in certain direction; and it is 

 this latter agency which answers to the survival of the fittest under 

 nature. 



CONTROLLED BY NATURAL SELECTION 



From the facts alluded to in the first chapter, I think there 

 can be no doubt that use in our domestic animals has strengthened 

 and enlarged certain parts, and disuse diminished them; and that 

 such modifications are inherited. Under free nature we have no 

 standard of comparison by which to judge of the effects of long- 

 continued use or disuse, for we know not the parent-forms; but 

 many animals possess structures which can be best explained by 

 the effects of disuse. As Professor Owen has remarked, there is no 

 greater anomaly in nature than a bird that cannot fly; yet there 

 axe several in this state. The logger-headed duck of South America 

 can only flap along the surface of the water, and has its wings in 

 nearly the same condition as the domestic Aylesbury duck: it is 

 a remarkable fact that the young birds, according to Mr. Cunning- 

 ham, can fly, while the adults have lost this power. As the larger 

 ground-feeding birds seldom take flight except to escape danger, 

 it is probable that the nearly wingless condition of several birds, 

 now inhabiting or which lately inhabited several oceanic islands, 

 tenanted by no beasts of prey, has been caused by disuse. The 

 ostrich indeed inhabits continents, and is exposed to danger from 

 which it cannot escape by flight, but it can defend itself, by 

 kicking its enemies, as efficiently as many quadrupeds. We may 

 believe that the progenitor of the ostrich genus had habits like 

 those of the bustard, and that, as the size and weight of its body 

 were increased during successive generations, its legs were used 

 more and its wings less, until they became incapable of flight. 



Kirby has remarked (and I have observed the same fact) that 

 the anterior tarsi, or feet, of many male dung-feeding beetles are 

 often broken off; he examined seventeen specimens in his own 

 collection, and not one had even a relic left. In the Onites apelles 

 the tarsi are so habitually lost that the insect has been described 

 as not having them. In some other genera they are present, but in 

 a rudimentary condition. In the Ateuchus or sacred beetle of the 

 Egyptians, they are totally deficient. The evidence that accidental 

 mutilations can be inherited is at present not decisive; but the 



