260 Darwin, and after Darwin. 



the fixed laws of heredity, it further follows that the 

 individuals composing each successive generation have 

 a general tendency to be better suited to their sur- 

 roundings than were their forefathers. And this 

 follows, not merely because in every generation it is 

 only the " flower of the flock " that is allowed to breed, 

 but also because, if in any generation some new and 

 beneficial qualities happen to arise as slight variations 

 from the ancestral type they will (other things per- 

 mitting) be seized upon by natural selection, and, being 

 transmitted by heredity to subsequent generations, will 

 be added to the previously existing type. Thus the 

 best idea of the whole process will be gained by com- 

 paring it with the closely analogous process whereby 

 gardeners, fanciers, and cattle-breeders create their 

 wonderful productions ; for just as these men, by 

 always "selecting" their best individuals to breed 

 from, slowly but continuously improve their stock, so 

 Nature, by a similar process of "selection" slowly but 

 continuously makes the various species of plants and 

 animals better and better suited to the conditions of 

 their life. 



Now, if this process of continuously adapting or- 

 ganisms to their environment takes place in nature 

 at all, there is no reason why we should set any limits 

 on the extent to which it is able to go, up to the 

 point at which a complete and perfect adaptation is 

 achieved. Therefore we might suppose that all species 

 would eventually reach this condition of perfect 

 harmony with their environment, and then remain 

 fixed. And so, according to the theory, they would, 

 if the environment were itself unchanging. But for- 

 asmuch as the environment (i. e. the sum total of the 



