The Factors of Evolution 



23'J 



whole question of selection can be had after a discussion of 

 the next factor of evolution, namely mutation. 



The mutation theory is not a new one to biologists. A 

 century ago St. Hilaire suggested the origin of birds from 

 reptiles, the first formed bird hatching full-fledged from a 

 reptile 's egg. The existence of mutants or l ' sports ' ' were well 

 known to Darwin, and are cited by him as a source, although 

 a minor one, of evolution. The cases which he gives are how- 



MUTATION IN (ENOTHERA 



The original stock lamarkiana to the left, gigas a mutant to the right. 

 From Castle, ''Genetics and Eugenics," 



By permission of Harvard University Press. 



ever of a striking and unusual sort. The Ancon ram is one 

 of these. In 1791 a Massachusetts farmer discovered in his 

 flock a ram with short crooked legs and a long body. The 

 thrifty farmer bred from this ram in order to obtain a flock 

 of sheep which could not jump fences, and would thereby 

 save himself much worry, and his sheep dog much exercise. 

 This was the origin of the famous breed of Aucon sheep, which 

 is now however extinct. The merino sheep, a breed having 

 long silky wool, which originated in 1828, is another exam- 



