CHAPTER IX. 



THE CAUSE OF THE INCREASE OF ,,VARIABILITY" 

 UNDER DOMESTICATION. 



It is almost generally believed that domestication 

 causes variation by the influence of better food or of 

 unusual food etc., giving rise to certain transmit- 

 table tendencies in the domesticated animals or 

 plants. 



So Darwin says: 



,,When we see an animal highly kept, producing off- 

 spring with an hereditary tendency to early maturity 

 ,,and fatness, when we see the wild duck, and the austra- 

 ,,lian dog, always becoming, when bred for one or a 

 ,,few generations in confinement, mottled in their co- 



,,lours we naturally attribute such changes to the 



,,direct effect of known or unknown agencies acting for 

 ,,one or more generations on the parents. It is possible 

 ,,that a multitude of peculiarities may thus be caused 

 ,,by unknown external agencies". 



Now we have seen that there is no proof for the 

 existence of a transmittable influence of external agen- 

 cies, so that we must look for another cause for the 

 changes we find that frequently follow upon confine- 

 ment of a wild animal. Darwin himself clearly recogni- 

 zed that there must be other causes for the greater 

 ,, variability" existing among domesticated animals and 

 plants, than this direct effect of external agencies, so 



