146 SECRETS OF EARTH AND SEA 



in Chapter X.), instead of being a trifling and unimportant 

 character, as was supposed by the older naturalists, is 

 really one of great significance, often correlated with 

 important constitutional differences. It is pointed out by 

 Alfred Wallace that in all the recorded cases in which a 

 decided infertility occurs between varieties (or races) of the 

 same species of plants (such as those just cited), those 

 varieties are distinguished by a difference of colour. He 

 gives reasons for thinking that the correlation of colour 

 with infertility which has been detected in several cases in 

 plants may also extend to animals in a state of nature. 

 The constant preference of animals — even mere varieties 

 of dog, sheep, horses, and pigeons — for their like, has 

 been well established by observation. Colour is one 

 of the readiest appeals to the eye in guiding animals 

 in such selection and association, and is connected with 

 deep-seated constitutional qualities. " Birds of a feather 

 flock together " is a popular statement confirmed by the 

 careful observation of naturalists. Thus we arrive at some 

 indication of features which may determine the inter- 

 breeding, or the abstention from inter-breeding, of diverse 

 races sprung from one original stock. The "colour 

 bar" is not merely the invention of human prejudice, 

 but already exists in wild plants and animals. 



We now come to the questions, the assertions, the beliefs, 

 and the acts concerning the inter-breeding of human races, 

 to the consideration of which I have been preparing the 

 way. The dog-fancier has generally a great contempt for 

 " mongrels." Breeders generally dislike accidental crosses, 

 because they interfere with the purpose which the breeder 

 has in view of producing animals or plants of a quality, 

 form, and character which he has determined on before- 

 hand. This interference with his purpose seems to be the 

 explanation of beliefs and statements, to the prejudice of 

 " mongrels." Really, as is well known to great breeders 



