THEORIES OF LAMARCK AND DARWIN 391 



strain and to survive. As another illustration, Darwin 

 pointed out that natural selection had produced a long-legged 

 race of prairie wolves, while the timber wolves, which have 

 less occasion for running, are short-legged. 



We can also see the operation of natural selection in the 

 production of the sharp eyes of birds of prey. Let us con- 

 sider the way in which the eyes of the hawk have been per- 

 fected by evolution. Natural selection compels the eye to 

 come up to a certain standard. Those hawks that are born 

 with weak or defective vision cannot cope with the conditions 

 under which they get their food. The sharp-eyed forms 

 would be the first to discern their prey, and the most sure in 

 seizing upon it. Therefore, those with defective vision or 

 with vision that falls below the standard will be at a very 

 great disadvantage. The sharp-eyed forms will be preserved 

 by a selective process. Nature selects, we may say, the 

 keener-eyed birds of prey for survival, and it is easy to see 

 that this process of natural selection would establish and 

 maintain a standard of vision. 



But natural selection tends merely to adapt animals to 

 their surroundings, and does not always operate in the direc- 

 tion of increasing the efficiency of the organ. We take an- 

 other illustration to show how Darwin explains the origin of 

 races of short-winged beetles on certain oceanic islands. 

 Madeira and other islands, as Kerguelen island of the Indian 

 Ocean, are among the most windy places in the world. The 

 strong-winged beetles, being accustomed to disport them- 

 selves in the air, would be carried out to sea by the sudden 

 and violent gales which sweep over those islands, while the 

 weaker- winged forms would be left to perpetuate their kind. 

 Thus, generation after generation, the strong-winged beetles 

 would be eliminated by a process of natural selection, and 

 there would be left a race of short-winged beetles derived 

 from long-winged ancestors. In this case the organs are 



