IN-BREEDING 227 



animals which produce large numbers of young at a birth 

 and have a comparatively short period of gestation. 

 Domestic swine fulfill these conditions admirably and 

 are therefore most valuable material for breeding experi- 

 ments. 



" Mr. J. Wright, well known as a breeder, crossed 

 the same boar with the daughter, granddaughter, and 

 great-granddaughter, and so on for seven generations. 

 The result was, that in many instances the offspring failed 

 to breed ; in others they produced few that lived ; and 

 of the latter many were idiotic, without sense, even to 

 suck, and when attempting to move could not walk 

 straight. Now it deserves especial notice, that the two 

 last sows produced by this long course of inter-breeding 

 were sent to other boars, and they bore several litters 

 of healthy pigs. The best sow in external appearance 

 produced during the whole seven generations was one 

 in the last stage of descent; but the litter consisted of 

 this one sow. She would not breed to her sire, yet bred 

 at the first trial to a stranger in blood. So that, in Mr. 

 Wright's case, long-continued and extremely close inter- 

 breeding did not affect the external form or merit of the 

 young; but with many of them the general constitution 

 and mental powers, and especially the reproductive func- 

 tions, were seriously affected." 



Nathusius reports that as a result of closely in-breed- 

 ing Yorkshire swine for three generations the offspring 

 were weak in constitution and their fertility was impaired. 



212. In-breeding sheep. The American Merino sheep 

 is a remarkable example of what intelligent breeding and 



1 Darwin, "Animals and Plants under Domestication," p. 

 101. 



Also Journal of Royal Agricultural Society, 1846, vol. 7, p. 205. 



