422 DARWINISM chap. 



these Amei'ican evolutionists have departed very widely from 

 the views of Mr. Darwin, and in place of the Avell-established 

 causes and admitted laws to which he appeals have introduced 

 theoretical conceptions which have not yet been tested by 

 experiments or facts, as well as metaphysical conceptions 

 which are incapable of proof. And when they come to 

 illustrate these \deAvs by an appeal to palaeontology or 

 morphology, we find that a far simpler and more complete 

 explanation of the facts is afforded by the established principles 

 of variation and natural selection. The confidence Avith Avhich 

 these new ideas are enunciated, and the repeated assertion 

 that A^thout them DarAvinism is poAA^erless to explain the 

 origin of organic forms, renders it necessary to bestoAV a little 

 more time on the explanations they give us of well-knoAvn 

 phenomena Avith Avhich, they assert, other theories are incom- 

 petent to grapple. 



As examples of use producing structural change, Mr. Cope 

 adduces the hooked and toothed beaks of the falcons and the 

 butcher-birds, and he argues that the fact of these birds belong- 

 ing to Avidely difterent groups proA^es that similarity of use has 

 produced a similar structural result. But no attempt is made 

 to shoAv any direct causal connection betAveen the use of a bill 

 to cut or tear flesh and the development of a tooth on the 

 mandible. Such use might conceivably strengthen the bill 

 or increase its size, but not cause a special tooth-like outgroAvth 

 Avhich Avas not present in the ancestral thrush-like forms of 

 the butcher-bird. On the other hand, it is clear that any 

 variations of the bill tending toAvards a hook or tooth aA' ould give 

 the possessor some advantage in seizing and tearing its prey, 

 and Avould thus be preserved and increased by natural selection. 

 Again, Mr. CojDe urges the eftects of a supposed " laAv of polar 

 or centrifugal groAvth " to counteract a tendency to un- 

 symmetrical groAA^th, AA'here one side of the body is used more 

 than the other. But the undoubted hurtfulness of Avant of 

 symmetry in many important actions or functions Avould 

 rapidly eliminate any such tendency. Allien, hoAvever, it has 



dress, namely, what is the meaning and importance of Professors Cope and 

 Hyatt's views ou acceleration and retardation ? I have endeavoured, and 

 given up iu desjiair, the attempt to grasji theu' meaning " {Life and Letters, 

 vol. iii. p. 233). 



