EVIDENCES OF ORGANIC EVOLUTION 35 



have no reason whatever for supposing that domesti- 

 cated species are more mutable than wild species, and 

 there is consequently every reason to believe that 

 changes of a similar character take place in Nature. 



Mr. Alfred Russel Wallace has quoted with approval 

 Sir W. Thiselton Dyer's criticism that if there is an 

 equal chance of the occurrence or origin of new forms 

 in nature and under cultivation, then their appearance 

 i.e., their survival until a stage at which they can 

 be readily recognized as distinct from the original type 

 should be more frequent in nature than in cultiva- 

 tion, because the former has a larger population to 

 work with. The reply to this argument is obvious. 

 In the first place, the much greater facilities for obser- 

 vation under cultivation may fairly be set against the 

 greater numbers stated to exist in nature ; but, in the 

 second place, Mr. Wallace may well be challenged to 

 cite a natural species of which a larger number of 

 individuals has passed under man's observation than 

 is the case with cultivated wheat, for example. But a 

 third line of argument is much more conclusive than 

 either of these. The modifications which occur under 

 cultivation are in most cases decidedly weakly as com- 

 pared with the original forms, as every gardener knows 

 to his cost. They are only enabled to survive to a 

 recognizable stage, because cultivation consists in the 

 removal of competition ; all are given an equal chance. 

 This is not so in nature. There, competition (according 

 to the exponents of the Wallacian doctrine) is so intense 

 that even very slight variations may determine success 

 or failure. According to the doctrine of natural selec- 



33 



