264 Darwin, and after Darwin. 
to survive, and so to perpetuate the improvement in 
his or her progeny. 
Now I say that all these several component parts 
of Darwinian doctrine are not matters of theory, but 
matters of fact. The only element of theory in his 
doctrine of evolution by natural selection has reference 
to the degree in which these observable facts, when 
thus brought together, are adequate to account for the 
process of evolution. 
So much, then, as a statement of the theory of 
natural selection. But from this statement—i. e. from 
the theory of natural selection itself—there follow 
certain matters of general principle which it is im- 
portant to bear in mind. These, therefore, I shall 
here proceed to mention. 
First of all, it is evident that the theory is applicable 
as an explanation of organic changes in specific types 
only in so far as these changes are of wse, or so far 
as such changes endow the species with better chances 
of success in the general struggle for existence. This 
is the only sense in which I shall always employ the 
terms use, utility, service, benefit, and so forth—that 
is to say, in the sense of life-preserving. 
Next, it must be clearly understood that the life 
which it is the object, so to speak, of natural selection 
to preserve, is primarily the life of the species ; not 
that of the zvdividual. Natural selection preserves 
the life of the individual only in so far as this is 
conducive to that of the species. Wherever the life- 
interests of the individual clash with those of the 
species, that individual is sacrificed in favour of others 
