NATURAL SELECTION 1509 



any organic being ever do occur, assuredly individ- 

 uals thus characterized will have the best chance of 

 being preserved in the struggle for life; and from 

 the strong principle of inheritance, these will tend 

 to produce offspring similarly characterized. This 

 principle of preservation, or the survival of the fit- 

 test, I have called Natural Selection. It leads to the 

 improvement of each creature in relation to its or- 

 ganic and inorganic conditions of life; and conse- 

 quently, in most cases, to what must be regarded as 

 an advance in organization. Nevertheless, low and 

 simple forms will long endure if well fitted for their 

 simple conditions of life. 



Natural selection, on the principle of qualities 

 being inherited at corresponding ages, can modify 

 the egg, seed, or young, as easily as the adult. Among 

 many animals, sexual selection will have given its 

 aid to ordinary selection, by assuring to the most vig- 

 orous and best adapted males the greatest number of 

 offspring. Sexual selection will also give characters 

 useful to the males alone, in their struggles or rivalry 

 with other males; and these characters will be trans- 

 mitted to one sex or to both sexes, according to the 

 form of inheritance which prevails. 



Whether natural selection has really thus acted, in 

 adapting the various forms of life to their several 

 conditions and stations, must be judged by the gen- 

 eral tenor and balance of evidence. But we have 

 already seen how it entails extinction; and how 

 largely extinction has acted in the world's history, 

 geology plainly declares. Natural selection, also, 

 leads to divergence of character; for the more or- 



