522 THE AMEBIC AN NATURALIST [Vol. LII 



the effect that the environment acting through long inter- 

 vals of time may impress characters upon an organism 

 which become unalterable by reversal processes. 



To these propositions may be added the suggestion of 

 the fundamental importance which physico-chemical 

 methods must play during the future in solving the prob- 

 lems of evolution. 



II 



The controversies relating to evolution have been 

 many. When, however, one considers the interest at- 

 tached to the subject, its broad bearing on various phases 

 of human welfare— sociology and economics in general, 

 animal and plant breeding in particular— together with 

 the difficulties of interpretation which apparently have 

 increased rather than diminished during the sixty or 

 more years seriously devoted to its elucidation, it is not 

 at all surprising that many different conclusions have 

 been reached, many dogmatic statements presented, and 

 many acrimonious discussions engendered. 



In connection with a clearer understanding of the 

 points at issue, it will be well to pass certain historical 

 details relating to the development of the different 

 theories somewhat critically in review. This is done 

 even at the risk of a repetition of facts quite familiar to 

 those who have taken more than a passing interest in the 

 subject. 



For long the theory of natural selection dependent on 

 the inheritance of small chance variations received gen- 

 eral acceptance. Championed by Weismann in his 

 notable controversy with Spencer to the exclusion of the 

 Lamarekian idea that characters acquired through en- 

 vironmental stimuli were heritable, it seemed at the time 

 entirely plausible as an explanation meeting the condi- 

 tions. 



With the greater attention given to experimental meth- 

 ods, however, doubt arose concerning the fundamental 

 value of selection and resulted in the presentation of the 

 mutation theory by DeVries. Here evolution was inter- 



