2 INTRODUCTORY [ch. 



find in natural selection alone a complete explanation 

 of the process of evolution, and to regard it as the 

 sole factor by which all evolutionary change is brought 

 about. Evolution on this view is a gradual process 

 depending upon the slow accumulation by natural 

 selection of small variations, which are more or less 

 inherited, till at last a well-marked change of type is 

 brought about. Could we have before us all the stages 

 through which a given form has passed as natural 

 selection transforms it into another, they would con- 

 stitute a continuous series such that even refined 

 scrutiny might fail to distinguish between any two 

 consecutive terms. If the slight variations are not of 

 service they will get no favour from natural selection 

 and so can lead to nothing. But if of use in the 

 struggle for existence natural selection preserves them 

 and subsequent variations in the same direction until 

 at length man recognises the accumulation as a new 

 form. Moreover when the perfect thing is once 

 elaborated natural selection will keep it perfect by 

 discouraging any tendency to vary from perfection. 



Upon this view, of which the most distinguished 

 protagonist was Weismann, natural selection is the sole 

 arbiter of animal and plant form. Through it and it 

 alone the world has come to be what it is. To it must 

 be ascribed all righteousness, for it alone is the maker. 

 Such in its extreme form is the modern development 

 of Darwin's great contribution to philosophy. 



But is it true ? Will natural selection really serve 

 to explain all ? Must all the various characters of 



