10 Darwinism and Other Essays. 



was simple, and admitted of precise mathematical 

 treatment ; and it is owing to this that the law of 

 gravitation has become the most illustrious exam- 

 ple which the history of science can furnish of a 

 completely verified hypothesis. 



To look for similar conciseness of verification 

 in the case of the Darwinian theory would be to 

 mistake entirely the conditions under which sci- 

 entific evidence can be procured. To estimate 

 properly the value of any hypothesis, it is neces- 

 sary that we should know what kind and degree 

 of proof to expect ; and in the present case we 

 must not look for a demonstration that shall be di- 

 rect and simple. Instead of a universal property 

 of matter, so conspicuous as to be recognized at 

 once by the inspection of a few striking instances, 

 we have in the theory of natural selection to 

 deal with a very complex process, working results 

 of endless diversity throughout the organic world, 

 and often masked in its action by accompanying 

 processes, some of which we can detect without 

 being able to estimate their relative potency, 

 while others, no doubt, have thus far escaped our 

 attention altogether. Accordingly, while we may 

 consider it as certain that natural selection is ca- 

 pable of working specific changes in organisms, we 

 may at the same time find it impossible to give a 



