Chap. XXII. CAUSES OF VARIABILITY. 263 



that there should be no crossing with domestic breeds, has 

 given, as previously stated, full details on the changes which they 

 gradually undergo. He found that he could not breed these wild 

 ducks true for more than five or six generations, " as they then 

 " proved so much less beautiful. The white collar round the neck 

 " of the mallard became much broader and more irregular, and 

 " white feathers appeared in the ducklings' wings." They in- 

 creased also in size of body ; their legs became less fine, and they 

 lost their elegant carriage. Fresh eggs were then procured 

 from wild birds ; but* again the same result followed. In these 

 cases of the duck and turkey we see that animals, like plants, 

 do not depart from their primitive type until they have been 

 subjected during several generations to domestication. On 

 the other hand, Mr. Yarrell informed me that the Australian 

 dingos, bred in the Zoological Gardens, almost invariably pro- 

 duced in the first generation puppies marked with white and 

 other colours ; but these introduced dingos had probably been 

 procured from the natives, who keep them in a semi-domesticated 

 state. It is certainly a remarkable fact that changed conditions 

 should at first produce, as far as we can see, absolutely no effect ; 

 but that they should subsequently cause the character of the 

 species to change. In the chapter on pangenesis I shall 

 attempt to throw a little light on this fact. 



Returning now to the causes which are supposed to induce 

 variability. Some authors 31 believe that close interbreeding 

 gives this tendency, and leads to the production of monstrosities. 

 In the seventeenth chapter some few facts were advanced, 

 showing that monstrosities are, as it appears, occasionally thus 

 caused; and there can be no doubt that close interbreeding 

 induces lessened fertility and a weakened constitution ■ hence it 

 may lead to variability : but I have not sufficient evidence on 

 this head. On the other hand, close interbreeding, if not car- 

 ried to an injurious extreme, far from causing variability, tends 

 to fix the character of each breed. 



It was formerly a common belief, still held by some per- 

 sons, that the imagination of the mother affects the child in 



?» Devay, 'Manages Consanguins,' pp. 97, 125. In conversation I have found 

 two or three naturalists of the same opinion. 



