338 DARWINISM STATED BY DARWIN HIMSELF. 



like tail, bearing a pair of feathers on each joint, and with 

 its wings furnished with two free claws, has been discov- 

 ered in the oolitic slates of Solenhofen. Hardly any re- 

 cent discovery shows more forcibly than this, how little 

 we as yet know of the former inhabitants of the world. 



THE EXTINCTION OF SPECIES INVOLVED IN MYSTERY. 



Origin of The extinction of species has been involved 



Species, in the most gratuitous mystery. Some au- 

 page . -fchors have even supposed that as the individ- 

 ual has a definite length of life, so have species a definite 

 duration. No one can have marveled more than I have 

 done at the extinction of species. When I found in La 

 Plata the tooth of a horse imbedded with the remains 

 of mastodon, megatherium, toxodon, and other extinct 

 monsters, which all co-existed with still living shells at a 

 very late geological period, I was filled with astonishment ; 

 for, seeing that the horse, since its introduction by the 

 Spaniards into South America, has run wild over the 

 whole country and has increased in numbers at an un- 

 paralleled rate, I asked myself what could so recently 

 have exterminated the former horse under conditions of 

 life apparently so favorable. But my astonishment was 

 groundless. Professor Owen soon perceived that the 

 tooth, though so like that of the existing horse, belonged 

 to an extinct species. Had this horse been still living, 

 but in some degree rare, no naturalist would have felt 

 the least surprise at its rarity ; for rarity is the attribute 

 of a vast number of species of all classes, in all countries. 

 If we ask ourselves why this or that species is rare, we 

 answer that something is unfavorable in its conditions of 

 life ; but what that something is we can hardly ever tell. 

 On the supposition of the fossil horse still existing as a 



