No. 542] DARWIN'S THEORY OF EVOLUTION 81 



in feral environment, and of domesticated characters in 

 return to domestication, e. g., barking in dogs. (19) 

 Ontogenic reactions to environment are observed in all 

 external and internal characters in animals and plants. 

 (20) Under selection Darwin anticipated the theory of 

 organic or coincident selection. 10 



Summary 



Darwin did not so sharply distinguish in language as 

 Weismann and Mendel have taught us to between the 

 different kinds of variation and different factors of evo- 

 lution, yet in his observations and the cases he cites his 

 perception is absolutely clear between heredity, ontogeny, 

 environment and selection as interoperating factors. In 

 fact, he remarks 11 on the frequent difficulty of distin- 

 guishing between the inextricably mingled factors of 

 ontogeny (e. g., effects of use and disuse), and of corre- 

 lated or coadapted variability and of spontaneous varia- 

 tions. A comparison of all the various kinds of varia- 

 tion cited by Darwin in his two great volumes shows that 

 they fall into the following four classes : 



I. ' * Individual variations, ' " ' spontaneous variations, ' ' 

 new suddenly appearing heritable characters, practically 

 equivalent to the minor mutations of De Vries, believed 

 by Darwin to be the chief material of natural selection 

 and evolution. 



II. Sports, or major saltations, such as the "man- 

 champ," "ancon" and "niata" breeds, believed by Dar- 

 win not to occur in a state of nature. 



III. Fluctuations of proportion, congenital and hence 

 transmissible, equivalent to the quantitative variation of 

 Bateson, best illustrated by Darwin in his theory of the 

 evolution of the long neck of the giraffe : 



So under nature with the nascent giraffe, the individuals which were 

 the highest browsers, and were able during dearths to reach even an 

 inch or two above the others, will often have been preserved; for they 



10 Vol. II, pp. 317, 318. 



n Vol. n, p. 327. 



