148 EVOLUTION 



reproductive system acting irregularly and 

 producing variations. But that variation is 

 aot exclusively associated with sexual repro- 

 duction is demonstrated by the case of plants 

 " sporting " through bud-variation. Such 

 cases, moreover, prove that the nature of the 

 organism counts for more than the conditions. 



Changed habits, e.g. changes in the degree 

 of use or disuse of a part, produce an inherited 

 effect, witness the lighter wing-bones and 

 heavier leg-bones of the domestic duck, or 

 the enlarged udders of cows. 



Variations are often definitely correlated : 

 thus short-beaked pigeons have small feet; 

 hairless dogs have imperfect teeth; and blue- 

 eyed white tom-cats are deaf. Hence selec- 

 tion of any one character will probably modify 

 others indirectly. 



Although the laws of inheritance are mostly 

 unknown, it seems that probably most, if not 

 all, characters tend to be inherited. There 

 is no satisfactory evidence to support the 

 popular idea that domestic varieties revert 

 to the primitive stock when they run wild. 

 Reversions occasionally occur in domestica- 

 tion, but there is no general tendency to lose 

 what has been gained apart, of course, from 

 breeding with wild stocks, or with other 

 domesticated ones. 



