SUMMARY. 241 



such firm support and to be so intimately connected 

 with Darwinism. But, nevertheless, natural selec- 

 tion has, with further study, proved inadequate to the 

 task which it attempts to solve. No one will deny 

 that it is a potent factor in nature, perhaps the most 

 potent which has been yet discovered ; but there is 

 much disagreement as to the limits of its power. 

 While Darwin would believe it the all-important 

 factor, making every thing else subservient to it, 

 other scientists would consider it as secondary and 

 of little importance. We have seen that even when 

 we admit the efficacy of the law in nature, it lacks a 

 complete explanation. It is based upon the exist- 

 ence of variations which are themselves unexplained. 

 To be sure these variations do undoubtedly occur, 

 as any one acquainted with animals and plants is 

 well aware, and it is easy to conceive that the in- 

 finite variety of circumstances under which different 

 animals are placed should cause varieties in bodily 

 structure. Such variations will have no relation to 

 the needs of the animal, will be indefinite in direc- 

 tion, occurring in only few individuals at a time* and 

 usually of slight importance. Unless we can give 

 a more fundamental explanation, such indefinite 

 variations are all that can be assumed. With these 

 variations Darwin has attempted to account for the 

 origin of species, but, as we have seen, he does not 

 completely succeed. If species have always arisen 

 slowly by minute variations, as they seem to be 

 doing to-day, the time since the solidifying of the 

 world has not been long enough to account for the 

 present species. The numerous transitional links 



