*30 ORGANIC EVOLUTION" 



now beginning to learn. Variation is not a sort 

 of " bad shot " at heredity, but has laws of its own, 

 and is itself a form of heredity. What is now 

 material for us, however, is merely to appreciate 

 the cardinal fact that heredity and variation are 

 essential conditions of evolution. What Darwin 

 called " natural selection " is the selection of favour- 

 able variations : this process could not take place 

 if variations did not occur, and would lead nowhere 

 if such variations were not transmitted and per- 

 petuated by heredity. 



There is here a- matter of terminology which it 

 is necessary clearly to understand. In the sense in 

 which the word is used by biologists and in this 

 book, variation is an inborn change. An individual 

 organism may undergo change by reason of the 

 peculiar conditions of its environment, and thus 

 may come to vary from its fellows ; every individual, 

 animal or vegetable, doubtless does so; but such a 

 change is not called a variation, but an acquirement. 

 This definition does not exclude the possibility 

 that a true variation may show itself only late in 

 the individual history, as may quite well be the 

 case even with characters which were truly inborn 

 ■ — latent in the germ. The distinction between a 

 variation and an acquirement is absolutely funda- 

 mental, and must never be lost sight of. 



Clearly understanding, then, the meaning which 

 attaches to these two words in biology ; and clearly 

 recognising that, in all theories of evolution — 

 Lamarckian, Darwinian, Weismannian — these con- 

 ditions, heredity and variation, are presupposed, we 

 may accept them as facts without here concerning 



