160 NATURAL SELECTION. [Chap. IV. 



dinary fact if no variations had ever occurred useful to 

 each being's own welfare, in the same manner as so 

 many variations have occurred useful to man. But 

 if variations useful to any organic being ever do occur, 

 assuredly individuals thus characterised 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 characterised. This 

 principle of preservation, or the survival of the fittest, I 

 have called Natural Selection. It leads to the improve- 

 ment of each creature in relation to its organic and inor- 

 ganic conditions of life; and consequently, in most 

 cases, to what must be regarded as an advance in organi- 

 sation. 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. Amongst many 

 animals, sexual selection will have given its aid to or- 

 dinary selection, by assuring to the most vigorous 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 transmitted 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 condi- 

 tions and stations, must be judged by the general tenor 

 and balance of evidence given in the following chapters. 

 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 



