SELECTION 157 



perfectly for a short time, Nature by con- 

 sistent accumulation during whole geological 

 periods. Natural selection is daily and hourly 

 scrutinizing, throughout the world, the slight- 

 est variations, rejecting those that are bad, 

 preserving and adding up all that are good, 

 silently and insensibly working, whenever and 

 wherever opportunity offers, at the improve- 

 ment of each organic being in relation to 

 its animate and inanimate conditions of life. 

 It may operate on characters which we are 

 apt to consider of very trifling importance, 

 and its accumulation of small variations may 

 set up unexpected correlative changes. It 

 may affect the egg, the seed, or the young as 

 easily as the adult; it may adapt the structure 

 of young to parent and of parent to young; 

 and in social animals it may adapt the struc- 

 ture of each for the benefit of all. In the later 

 editions of the " Origin " a brief account of 

 sexual selection is given at this point. 



The theory of natural selection is then illus- 

 trated by particular instances. Thus Darwin 

 pictures the formation of swift varieties of 

 wolves, much in the same way as greyhounds 

 have been evolved by man. Or, again, he 

 refers to the secretion of nectar by flowers, 

 its use to insects, the action of these in carry- 

 ing the fertilizing pollen, its advantage ia 



