50 DARWINISM STATED BY DARWIN HIMSELF. 



EFFECTS OF THE USE AND DISUSE OF PAETS. 



Origin of From the facts alluded to in the first chap- 



Species, ter, I think there can be no doubt that use in 

 page 108. ^^j, ^Qmggtig 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 can not fly ; yet there are sev- 

 eral 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. Cunningham, 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 beast of prey, has been 

 caused by disuse. The ostrich, indeed, inhabits conti- 

 nents, and is exposed to danger from which it can not 

 escape by flight, but it can defend itself by kicking its 

 enemies as efiSciently as many quadrupeds. We may be- 

 lieve 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 be- 

 came incapable of flight. 



