i.] DARWINISM VERIFIED. 19 



are best adapted to a given set of exigencies, we see 

 that, as the combinations of exigencies are altered from 

 time to time, the stability of species can in general 

 be but temporary. Now and then we may expect to 

 find very long persistency of type where, in spite of 

 great terrestrial changes, some simple set of condi- 

 tions most important to the organism remains un- 

 altered ; but in the vast majority of cases such per- 

 sistence is impossible. It is seldom that the life of 

 any species extends over more than one geological 

 epoch ; often the duration is much shorter than 

 this. 



Whether, therefore, it is practicable for us to-day 

 to explain every minute peculiarity of any one par- 

 ticular species by an appeal to natural selection 

 alone, is not the main point to be considered in esti- 

 mating the success of the Darwinian theory. The 

 question has a scientific interest of its own which is 

 very great, but it is not the main question. The 

 main point is that, admitting natural selection to be 

 a vera causa at all (and this no one denies), the 

 stability of species is proved to be but a contingent 

 and temporary affair. The old notion of an absolute 

 fixity of species is overthrown once for all, and with 

 it the only semblance of an argument that could 

 ever have been alleged in behalf of the hypothesis 



C 2 



