87 



per cent., the green snake 23 per cent., and the ring-necked snake 23.5 per 

 cent. In proportion of tail to body the garter snake varies 9.4 per cent., 

 the black snake 28 per cent., the green snake 25 per cent., and the ring- 

 necked snake over 35 per cent. There is scarcely a doubt that every 

 character in each of these species will be found to be as unstable as those 

 which have been studied. And it must be observed, too, that each of the 

 characters varies independently of the others, so that we may get any 

 combination that we may want. If breeders should find it to their inter- 

 ests to raise a varied assortinent of black snakes they could, doubtless, by 

 careful selection and crossing, produce short-bodied snakes with long 

 tails, long-bodied snakes with short tails, or snakes extremely short or 

 very long in both parts. Much more might we expect that natural se- 

 lection, which has more abundant materials to work upon and unlimited 

 time, should be able to produce varieties and species to suit the require- 

 ments of the changing conditions of geological periods. 



While the main proposition of Darwin and Wallace that species arise 

 from earlier species by descent with modification, has been almost unani- 

 mously accepted by the scientific world, a number of scientific authorities 

 have, within recent years expressed more or less dissatisfaction with the 

 prominence that Darwin and Wallace and their followers have given to 

 the doctrine of Natural Selection as an explanation of organic evolution. 

 This dissent has expressed itself in degrees from questioning whether or 

 not natural selection has been the only factor concerned, to open decla- 

 rations that it has had little or nothing to do with evolution. ( )f course, 

 those who deny the efliciency of selection to transform species endeavor 

 to find some other principles or forces which, in their estimation, act as 

 efficient causes, and thus we are beginning to witness the evolution of 

 various schools of evolution. And here it seems proper, as a matter of 

 justice to Darwin, to deny that he, at least in his later works, maintained 

 that natural selection is the only influence at work to bring about changes 

 in organisms. One cannot read his works with even moderate attention 

 without recognizing that he admitted the operation of the very forces 

 and principles that many of these later evolutionists rely on to explain 

 the phenomena of organic change. < )nly Darwin did not assign the same 

 high value to these factors that some authors do now. Wallace, ijn the 

 other hand, in his latest work advocates the earlier position of Darwin, 

 and stands for what he calls the "overwhelming importance of Natural 

 Sele<tion over all other agencies in the production of new species." 



