173 



Genetics and Evolution 



The Material Basis of Evolution. By Richard Goldschmidt. Yale Univer- 

 sity Press. 436 pp. 1940. $5.00. 



For over two thousand years men have been considering the 

 idea of evolution as an explanation of the origin of living things 

 as they exist today. John M. Coulter (Science, 1926) divided 

 the history of evolution into three periods: Speculative, to 1790; 

 Observation and Inference, 1790-1900; and Experimental, 1900 

 to date. Each of these periods may be said to have made certain 

 definite contributions to the progress of the whole concept. Through 

 speculation men came to realize that there are only three or four 

 conceivable explanations for existence of present-day living things, 

 viz., special creation, spontaneous generation, evolution, with the 

 "cosmozoa" concept as a possible fourth. As more and more data 

 were accumulated in the field of biology and in other sciences, it 

 became obvious that only one of the four was susceptible of factual 

 substantiation, and the speculative period ended when the pur- 

 poseful assembling of supporting evidence for evolution began. 



This second or inductive period reached its climax wath the 

 appearance of Darwin's "Origin of Species," w-hen the overwhelm- 

 ing weight of all the facts obtained from the study of the distribu- 

 tion of living things in time and in space, from comparative 

 anatomy, embryology, and the rest, combined to carry conviction 

 as to the historicity of the evolutionary process. In the forty years 

 which followed 1859, little more was accomplished in a fundamental 

 way except through the addition of many more positive data, and 

 the recognition that there was little if any evidence for which a 

 negative interpretation could be given. It did become clear, how- 

 ever, that little was really settled as to the method of evolution. 

 Attention was therefore focussed on the necessity for the experi- 

 mental study of variation and inheritance as to the focal processes 

 in any evolutionary change. 



With Mendel's rediscovered experiments as a basis, the con- 

 centrated attack of many investigators, using many different organ- 

 isms, especially in the fields of experimental breeding and cytology, 

 have combined to unravel many problems. The reasons why off- 

 spring resemble or differ from their parents seem to have been 

 pretty well elucidated. So complete has the solution of the prob- 

 lem of variation seemed to many of those who have gro\\-n up in 



