CHAPTER V 



THE PRINCIPLE AS MANIFESTED IN 

 THE ANIMAL KINGDOM 



THE amount of evidence available as to the operation 

 of the principle in the animal kingdom is comparatively 

 limited. We are compelled to rely chiefly on the evidence 

 supplied by the effect of change of environment on domes- 

 ticated animals, and the effect of captivity on wild animals. 

 It is of little use in this connection to make comparisons 

 between the fertility of wild and domesticated animals. 

 These latter have been adapted to the requirements of 

 man by a course of selection extending over innumerable 

 generations, and fertility is one of the attributes for which 

 they have been selected. 



It is true Darwin says that with " cats, ferrets, and 

 dogs," and other animals " which are not valued for their 

 prolificacy, selection can have played only a subordinate 

 part " 1 ; but to this it may be replied that prolificacy 

 is always a valuable quality in a valuable animal. Ex- 

 perience with wild animals in captivity shows that when 

 animals were first domesticated they would probably be 

 relatively infertile. Darwin has himself shown that the 

 principle of selection is in some measure understood even 

 by primitive tribes. It is impossible to imagine that 

 people who were capable of domesticating wild animals, 

 an extremely difficult feat, would be blind to the fact 

 that they would be more likely to obtain a large number 



1 Variation of Animals and Plants under Domestication, chap. xvi. 



n 



