6 INTRODUCTION 



by the action of natural selection upon minute differ- 

 ences, in the manner which Darwin described, and 

 which has been claimed by others as the sole means 

 by which the origin of new forms takes place. The 

 evidences of evolution are much more numerous and 

 more weighty than the evidences of the survival of 

 the fittest. The theory of evolution, as opposed to 

 the creation hypothesis, is supported by innumerable 

 facts of classification, of morphology, and of embryo- 

 logy, by the geographical distribution of animals and 

 plants, and by their succession in the geological strata* 

 as well as by direct observation of the actual occurrence 

 of changes in the case of domestic productions as well 

 as under Nature, and many of these facts have no 

 direct bearing upon the theory of natural selection. 



Before discussing the problem of the origin of species, 

 it is necessary to arrive at some idea as to what the 

 term * species ' means. And this is not altogether an 

 easy matter, since a precise definition has not been, 

 and cannot be, agreed upon. The idea of species is, 

 indeed, of great antiquity and very gradual growth. 

 Primitive men doubtless recognised certain plants or 

 animals as being like one another, and different from 

 others, and they gradually came to distinguish such 

 forms by giving a different name to each. The names 

 first used must have applied as a rule to genera rather 

 than to species. Thus, such common names of plants 

 as rose, bramble, vetch, nettle, dock, crowfoot, are 

 names of genera groups of greater extent than species, 

 and often more easily defined than the latter. Later 



