6 INTRODUCTION, 



would liold the progeny of a single pair after a certain num'ber 

 of generations. The inevitable result is an ever-recurrent 

 Struggle for Existence. It has truly been said that all 

 nature is at war ; the strongest ultimately prevail, the 

 weakest fail ; and we well know that myriads of forms have 

 disappeared from the face of the earth. If then organic beings 

 in a state of nature vary even in a slight degree, owing to 

 changes in the surrounding conditions, of which we have 

 abundant geological evidence, or from any other cause ; if, 

 in the long course of ages, inheritable variations ever arise 

 in any way advantageous to any being under its excessively 

 complex and changing relations of life ; and it would be a 

 strange fact if beneficial variations did never arise, seeing 

 how many have arisen which man has taken advantage of for 

 his own profit or pleasure ; if then these contingencies ever 

 occur, and I do not see how the probability of their occur- 

 rence can be doubted, then the severe and often-recurrent 

 struggle for existence will determine that those variations, 

 however slight, which are favourable shall be preserved 

 or selected, and those which are unfavourable shall be 

 destroyed. 



This preservation, during the battle for life, of varieties 

 which possess any advantage in structure, constitution, or 

 instinct, I have called Natural Selection ; and Mr. Herbert 

 Spencer has well expressed the same idea by the Survival of 

 the Fittest. The term " natural selection " is in some respects 

 a bad one, as it seems to imjDly conscious choice ; but this 

 Avill be disregarded after a little familiarit3^ No one objects 

 to chemists speaking of " elective affinity ; " and certainly an 

 acid has no more choice in combining with a base, than the 

 conditions of life have in determining whether or not a new 

 form be selected or preserved. The term is so far a good 

 one as it brings into connection the production of domestic 

 races by man's power of selection, and the natural preserva- 

 tion of varieties and species in a state of nature. For brevity 

 sake I sometimes speak of natural selection as an intelligent 

 power ; — in the same way as astronomers speak of the attrac- 

 tion of gravity as ruling the movements of the planets, or 

 as agriculturists speak of man making domestic races by his 



