DIRECT ADAPTATION, 23 1 



in our zoological gardens, and exotic plants which are grown 

 in our botanical gardens, are no longer able to reproduce 

 themselves. This is the case, for example, with most birds of 

 prey, parrots, and monkeys. The elephant, also, and the 

 animals of prey of the bear genus, in captivity hardly ever 

 produce young ones. In like manner many plants in a cul- 

 tivated state become sterile. The two sexes may indeed 

 unite, but no fructification, or no development of the fructi- 

 fted germ, takes place. From this it follows with certainty 

 that the changed mode of nutrition in the cultivated state is 

 able completely to destroy the capability of reproduction, 

 and therefore to exercise the greatest influence upon the 

 sexual organs. In like manner other adaptations or varia- 

 tions of nutrition in the parental organism may cause, not 

 indeed a complete want of descendants, but stiU important 

 changes in their form. 



Much better known than the phenomena of indirect or 

 potential adaptation are those of direct or actual adapta- 

 tion, to the consideration of which we now turn our at- 

 tention. To them belong aU those changes of organisms 

 which are generally considered to be the results of practice, 

 habit, training, education, etc. ; also those changes of or- 

 ganic forms which are effected directly by the influence of 

 nutrition, of climate, and other external conditions of exist- 

 ence. As has already been remarked in direct or actual 

 adaptation, the transforming influence of the external cause 

 affects the form of the organism itself, and does not only 

 manifest itself in that of the descendants. (Gen. Morph. 

 ii. 207.) 



We may place the law of universal adaptation at the 

 head of the different laws of direct or actual adaptation, 



