ADAPTIVE VARIATIONS. 395 



place have very few characters adapting it to an aquatic 

 existence, and so the curve of distribution of such char- 

 acters will be a more steeply sloped one than that for 

 plants. Also the direct effect of environment in the 

 direction of adaptation will be very much less than in 

 the case of plants, even after exposure for a large num- 

 ber of generations. In fact, to effect any real and con- 

 siderable change it will be essential to call in the aid 

 of Natural Selection, and this, by acting constantly for 

 a very large number of generations^ will gradually 

 evolve a typical aquatic mammal such as the seal, dol- 

 phin, or whale. 



In spite of all that has been written to account for 

 the almost universally present adaptation which we 

 see in animate nature, there is still a lingering doubt 

 in the minds of many men as to the entire adequacy of 

 the explanations hitherto offered. It is a feeling such 

 as this which prompted Weismann to formulate an ad- 

 ditional principle in explanation of adaptation, and of 

 other phenomena, as the degeneration of disused organs, 

 viz., his theory of Germinal Selection.* This theory 

 supposes that, similar to the struggle for existence ex- 

 perienced by individual organisms, so there is a strug- 

 gle among the determinants of the germ-plasm of each 

 single individual to obtain as great a supply of nutri- 

 ment as possible, and so flourish at the expense of 

 weaker determinants. Supposing, for instance, that 

 parts of the body, such as the hinder extremities of the 

 quadruped ancestors of our common whales, are ren- 

 dered useless. As selection ceases, individuals with 



*"Ueber Germinal Selection," Jena, 1896 (English translation, 

 Chicago, 1896). 



