DARWIN-. 179 



between sparrows and other birds, grows yearly 

 more severe. Each year now the sparrow gains a 

 little and the other birds lose correspondingly; but 

 sooner or later with each species a point will be 

 reached when the loss exactly balances the in- 

 crease. This produces a condition of apparent 

 equilibrium, — the equilibrium of Nature ; a sort of 

 armed neutrality which a superficial observer mis- 

 takes for real peace and permanence. But this 

 equilibrium is broken as soon as any individual 

 or group of individuals appears that can do some- 

 thing more than merely hold their own in a struggle 

 for existence. Slight deviations from the ancestral 

 type, for better or worse, are constantly appear- 

 ing in Nature. Of the infinite number of these 

 small variations which may affect the individual, 

 some will be found to be of advantage to him in 

 this struggle for existence. Be it ever so slight, 

 this help in time will count. The individuals thus 

 aided will live and multiply, and their type is the 

 type of the species preserved. Those individuals 

 Avho do not share this advantage, or who may be 

 handicapped by disadvantageous variation, die and 

 leave no descendants. Thus the advantage of the 

 individual becomes the gain of the species, and 

 thus in the character of the species does the fitness 

 of the individual survive. 



It is this progress through competition, this sur- 

 vival of the fittest to live in the struggle for exist- 

 ence, to which the term " natural selection " has 

 been applied. Different estimates of the relative 

 importance of the action of natural selection and 

 of other agencies modifying the history of a species 



