THE ANCESTRY OF THE HORSE 173 



titles as " Clique, the horse with six feet," 

 " the eight- footed Cuban horse," and so on ; 

 and possibly some of these are famiUar to 

 readers of this page. 



So the collateral evidence, though scanty, 

 bears out the circumstantial proof, derived 

 from fossil bones, that the horse has developed 

 from a many-toed ancestor ; and the evidence 

 points toward the little Hyracothere as being 

 that ancestor. It remains only to show some 

 good reason why this development should 

 have taken place, or to indicate the forces by 

 which it was brought about. We have heard 

 much about "the survival of the fittest," a 

 phrase which simply means that those animals 

 best adapted to their surroundings will sur- 

 vive, while those ill adapted will perish. But 

 it should be added that it means also that the 

 animals must be able to adapt themselves to 

 changes in their environment, or to change 

 with it. Living beings cannot stand still in- 

 definitely ; they must progress or perish. And 

 this seems to have been the cause for the ex- 

 tinction of the huge quadrupeds that flour- 

 ished at the time of the three-toed JNIiocene 



