172 SCIENCE REMAKING THE WORLD 



who offered these explanations are not responsible for 

 the idea of evolution, but merely attempted to explain 

 the fact of evolution. They were explainers rather 

 than authors. It is also important to realize the 

 method used. It may be called the method of compari- 

 son and inference. Plant and animal forms were ob- 

 served, and resemblances were assumed to indicate re- 

 lationship through descent. It was not demonstration, 

 but inference based on observation. Darwin carried 

 the method to the limit of its possibilities, observing not 

 a small range of forms, but observing through several 

 years a world-wide range of forms, in connection with 

 the famous voyage of the Beagle. His caution is also 

 indicated by the fact that his observations were under 

 consideration for some twenty years before his con- 

 clusions were published. His facts were so undoubted, 

 and his case so well put, that his explanation of evolu- 

 tion attracted immediate attention and really fought the 

 battle of evolution. This is what made his explanation 

 an epoch in the history of biological science. 



This period in the history of evolution, which may be 

 thought of as the mediaeval period, is marked by the 

 appearance of three conspicuous explanations. There 

 is no need to define these explanations in detail. The 

 explanation which ushered in the period was proposed 

 simultaneously and independently by Goethe of Ger- 

 many, St. Hilaire of France, and Erasmus Darwin of 

 England, in 1790. Observations of responses to 

 changed environment, led to the conclusion that en- 

 vironment is the direct cause of change, actually mould- 

 ing forms. This evolutionary factor, therefore, is 



