40 NATURAL SCIENCE. January. 



supposes the facts to have upon any of his theses, Professor Cope does 

 not, so far as I can discover, deign to tell us ; nor is it clear how the 

 facts of successional relation in time are more valuable evidence than 

 those of successional relation in space, which were dealt with in the 

 first chapter. 



The facts of retrogressive evolution or degeneration, which 

 Professor Cope calls Catagenesis, are discussed in Chapter IV., and 

 are supposed to prove the direct influence of disuse ; but no attempt is 

 made to combat the arguments of many who believe themselves to 

 have shown that degeneration is merely a form of adaptation to 

 surroundings, perfectly explicable on the principles of natural 

 selection. 



At this stage Professor Cope points out the conclusions he thinks 

 he has reached. For my part, while prepared to admit that 

 ** phylogeny exhibits a progressive advance along certain main lines," 

 and that evolution itself has been in definite directions, I cannot see 

 that it has been proved that all or even the majority of variations were 

 in definite directions. Definite variation may be possible, may exist, 

 may be of constant occurrence ; but as an attempt to prove it, these 

 200 pages seem to me utterly beside the point. 



We come now to the second part of the book, and as this is 

 entitled " The Causes of Variation," we look for something in support 

 of the thesis that variations are caused by the interaction of the 

 organism and its environment. Instead of this we find a lengthy and 

 highly interesting account of various methods in which modifications 

 are produced by the direct action of external influences, among which 

 are included the mechanical actions of the parts of the organism itself. 

 Everyone may not agree with everything here brought forward, but 

 none can be prepared to deny all the instances. Let us, for the sake 

 of the argument, admit modifications of the adult or of the growing 

 organism to the extent that Professor Cope desires. The question 

 remains : are these modifications inherited ? Throughout this section 

 such inheritance is boldly assumed by the author, and so all difficulties 

 disappear. But the mere existence of modifications, or the occurrence 

 of evolutionary series, the goal of which appears to be not merely 

 definite but adaptive, of themselves prove nothing. Undoubtedly, if 

 one could prove modifications to be inherited, one would have a 

 simple and satisfactory explanation of a very large number of facts 

 which at present have to be explained as due to some exceedingly 

 tortuous process, and one that many straightforward people find 

 difficult of conception. But we must remember how unsafe it is to 

 assume that simplicity is the rule in nature. 



Palaeontologists, as a rule, — and Professor Cope is one of them — 

 are so profoundly impressed by the adaptive nature of the evolutionary 

 process and by the definiteness of its direction, that they cannot 

 regard the restraining or selective action of the environment as enough 

 to keep the breed true. They are so accustomed to see mutation 



