118 EVOLUTION 



be readily sifted out from the slumped total. 

 Others may be wrapped up with age, and these 

 can also be analyzed out. Others are due 

 to something unusual in the " nurture " in 

 the wide sense; that is, they are the direct 

 results of peculiarities in surrounding influ- 

 ences and of peculiarities of habit. Such 

 changes in the bodies of plants and animals 

 are extrinsic, not intrinsic, in origin; they are 

 acquired, not inborn. They are technically 

 called " acquired characters," or much more 

 clearly " modifications." They may be de- 

 fined as structural changes in a part of the 

 body, directly induced by peculiarities of use 

 or disuse, or by some change in surroundings 

 and nurture generally, which transcend the 

 limit of organic elasticity and thus persist 

 after the inducing conditions have ceased to 

 operate. No convincing evidence of their 

 transmission has as yet been forthcoming. 



Now the point is that when we subtract 

 from the total of observed differences all that 

 can be regarded as individual modifications, 

 we have a very interesting remainder, which 

 we thus define off as inborn or germinal 

 variations. They are intrinsic, not extrinsic; 

 inborn, not made. We cannot causally relate 

 them in a direct way to peculiarities in habits 

 or surroundings; they are often distinct at 





