PAPERS PRESENTED AT GENERAL SESSIONS 33 



nothing new. It is the appearance of new things that 

 leads from one great group to another. 



Another subsidiary explanation is called " isolation," 

 which certainly accounts for the survival of variations 

 that might otherwise have been swamped out by crossing 

 and competition. After all it is a method of natural 

 selection; that is, selection is usually made by competi- 

 tion, but sometimes by isolation. 



Now, however, we are in the modern period in the 

 history of evolution. Darwin carried the method of 

 observation and inference to its limit in space and time, 

 but inference is not demonstration. At present we are 

 developing the technique of demonstration, by opening 

 up the great field of heredity, which is not only vast in 

 extent, but also extremely complex. When a species 

 ordinarily begets its own kind, according to well defined 

 laws of inheritance, what are the very occasional condi- 

 tions that make it beget or at least start another species'? 

 At the present time, therefore, attention is being focused 

 upon the experimental study of inheritance, the field of 

 genetics, which may be rightly called also the experi- 

 mental study of evolution. This newly developed field of 

 genetics, with its increasing complexities, has taught us 

 that evolution is a very intricate process, and that some 

 of the earlier explanations, like that of Darwin for ex- 

 ample, deal only with the more superficial phenomena. 

 They are true as far as they go, but they do not get at 

 the fundamentals. To say that evolution is discredited 

 because Darwin's explanation does not explain the whole 

 situation would be like discrediting the rotation of the 

 earth because some one explanation is not satisfactory. 

 It was in recognition of this modern genetical attack 

 upon the problems of evolution, with its multiplying com- 

 plications, that Bateson spoke of evolution as he did, 

 as a problem not yet solved. Of course, any explanation 

 of evolution must take into account the machinery of 

 heredity, and we are finding that machinery not only 

 complicated, but now and then producing unexpected 

 results, which the geneticist must explain. 



Naturally, this intensive study of evolution through 

 experimental work in inheritance has somewhat 



