The Mutation Hypothesis. 63 



express themselves more or less definitely in favor of 

 the mutation hypothesis. 



E. D. Cope was the first to clearly formulate objec- 

 tions against the doctrine of selection. Selection pre- 

 serves the good and weeds out the bad, but whence does 

 the good arise? Obviously ordinary variability is not 

 sufficient, and causes of an entirely different kind must 

 be sought for. Such causes he includes under the term 

 bathmism. 



Carl Semper similarly rejects the selection theory 

 and ascribes considerable importance to the influence of 

 the environment, the so-called monde ambiant of the 

 French school, in originating useful specific characters. 



Louis DoLLO was the first to express the view that 

 revolution est discontinue from the standpoint of the 

 theory of descent. He supports his statement by a series 

 of facts, partly zoological, partly botanical, but especially 

 derived from his own researches in paleontology. He 

 puts forth the additional proposition that revolution est 

 irreversible et limit ce.^ 



According to Wallace^s selection theory, progres- 

 sive change by artificial and natural selection is supposed 

 to be unlimited and even reversible. It must be reversed 

 according to Wallace as soon as the conditions on which 

 the selection depends are themselves reversed. According 

 to the mutation theory, on the other hand, no cause can 

 be assigned which would make a mutation reversible, 

 apart from the loss or latency of characters. Each 

 mutation is a definitely circumscribed unit. 



About a year later there appeared Bateson's famous 

 work Materials for the Study of Variation Treated 



^ Louis Dollo, Lcs Lois dc f evolution. Bull. Soc. Bclgc de Geo- 

 logic, T. VII, p. 164, Annee 1893. 



