Recent Developments in Heredity and Evolution 7 



The seven categories of facts thus indicated, and others 

 that might be added to them, will explain why a number 

 of scientific men were so impressed by the idea that organic 

 evolution is a fact, that they thought it important to 

 search for an explanation of the process. 



3. THE EXPLANATION OF EVOLUTION 



To accept organic evolution as a fact, and to explain 

 it as a process are two very different things, and must be 

 kept clearly distinct. The failure to distinguish them has 

 led recently to much confusion in popular statement and 

 belief. For example, the more exact work of recent years 

 has developed a considerable body of criticism against 

 Darwin 's theory of natural selection. To those who thought 

 of the theory of organic evolution as belonging to Darwin, 

 these criticisms seemed to indicate that belief in organic 

 evolution was tottering; when in fact, if any belief was 

 tottering, it was a belief in natural selection as a sufficient 

 explanation of the process of evolution. Darwin 's explana- 

 tion, Lamarck's explanation, every explanation hitherto 

 proposed, may be found inadequate, and still organic 

 evolution will remain to be explained. It must be remem- 

 bered that the work of biologists has been to explain the 

 fact of organic evolution, not to propose it as an idea; and 

 the destruction of no explanation can weaken the fact. 



A single address does not permit the mention of all the 

 proposed explanations of organic evolution, but a few domi- 

 nating ones may be selected as illustrations. The selection 

 is made with a full appreciation of the fact that profes- 

 sional biologists may think that others should be included. 



It is important to distinguish between the two methods 

 of attacking the problem. The earlier method, and the 



