INDIRECT EQUILIBRATION. 531 



favoured races in the struggle for life." That there goes 

 on a process of this kind throughout the organic world, Mr. 

 Darwin's great work on the Origin of Species has shown to 

 the satisfaction of nearly all naturalists. Indeed, when once 

 enunciated, the truth of his hypothesis is so obvious as 

 scarcely to need proof. Though evidence may be required to 

 show that natural selection accounts for everything ascribed 

 to it, yet no evidence is required to show that natural selec- 

 tion has always been going on, is going on now, and must 

 ever continue to go on. Recognizing this as an a priori cer- 

 tainty, let us contemplate it under its two distinct aspects. 



That organisms which live, thereby prove themselves fit for 

 living, in so far as they have been tried, while organisms which 

 die, thereby prove themselves in some respects unfitted for 

 living, are facts no less manifest than is the fact that this self- 

 purification of a species must tend ever to insure adaptation 

 between it and its environment. This adaptation may be 

 either so maintained or so produced. Doubtless many 



who have looked at Nature with philosophic eyes, have ob- 

 served that death of the worst and multiplication of the 

 best, tends towards maintenance of a constitution in harmony 

 with surrounding circumstances. That the average vigour of 

 any race would be diminished did the diseased and feeble 

 habitually survive and propagate; and that the destruction 

 of such, through failure to fulfil some of the conditions to life, 

 leaves behind those which are able to fulfil the conditions to 

 life, and thus keeps up the average fitness to the conditions 

 of life; are almost self-evident truths. But to recognize 

 " Natural Selection " as a means of preserving an already- 

 established balance between the powers of a species and the 

 forces to which it is subject, is to recognize only its simplest 

 and most general mode of action. It is the more special 

 mode of action with which we are here concerned. This 



more special mode of action, Mr. Darwin has been the first 

 to recognize as an all-important factor, though, besides his 

 co-discoverer Mr. A. R. Wallace, some others have perceived 



