VARIATION. 109 



breed are analysed, they resolve themselves 

 into differences in respect of size, quality, or 

 shape of certain muscles or bones. The two 

 animals remain the same, or at least similar, 

 in form, and no difference of a specific char- 

 acter between their skeletons or organs can 

 be detected ; but, on the contrary, the longer 

 selective breeding is pursued, the more firmly 

 established becomes even the family expres- 

 sion of a herd. The differences from the 

 average type, induced by selective breeding, 

 are only such as might be expected in the 

 progeny of selected animals, provided with 

 abundance of food and healthy comfortable 

 conditions of existence. Again, as might be 

 expected, wild beasts neither carefully se- 

 lected for breeding, nor reared under excep- 

 tionally favourable conditions, show less 

 divergence from an average type than pro- 

 tected domestic animals. 



The greater differences among domestic 

 than among wild animals probably arise, in 

 part, because the former were endowed with 

 an organisation of greater elasticity and 

 flexibility, and in consequence respond freely 

 to the influence of man. 



It is assumed by Darwin and other natur- 

 alists that all domestic animals came from 

 the closely allied wild species, but of this 



