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 



