NATURAL SELECTION 17 



of other desirable qualities. Variation is much more exten- 

 sive than we usually think, and such divergence in many 

 qualities at once might readily be found. 



Illustrations of this principle of natural selection might 

 be indefinitely multiplied. The environment presses upon 

 the animal or plant at all points, and the whole organism 

 is capable of adaptive response, since the whole organism 

 varies, giving favorable peculiarities for selection. Any 

 feature, of structure or of function, may be perfected when- 

 ever it becomes desirable to have it emphasized. The only 

 things necessary are that the useful character shall be pres- 

 ent year after year as a variation in some individuals, and 

 that it shall be of sufficient importance to aid its possessors 

 to win in the struggle for life in which they are constantly 

 engaged. This struggle is so severe that only the most 

 perfectly endowed can hope to win ; so that an advantage, 

 though very slight, may determine survival, or, as Romanes 

 puts it, be " of selection value." 



There are two quite different methods used by both 

 plants and animals to enable the several species to persist 

 and not be destroyed in the battle of life. The first is 



t 



the one already illustrated, namely, the gradual establish- 

 ment, by selection of the most perfect individuals, of a 

 condition of more perfect adaptation of the individuals of 

 the species to the environment in which it lives. The sec- 

 ond is to so greatly increase the number of the offspring 

 by great development of the reproductive functions, that 

 from very numbers they will have more chance of survival. 



J ^ 



We can hardly say that a million starfish eggs have a mill- 

 ion times more chance of survival than would one, but 

 surely a starfish that lays a million eggs has much more 



