Preface 



Theee are fashions in science as in all other things, and the study of 

 evolution is at present highly fashionable among biologists. This is re- 

 flected not only by the immense number of technical papers on various 

 aspects of evolution which are published annually, but also by the fact that 

 courses in evolution are presented in many colleges and universities, while 

 most courses in biological departments deal with evolution to some extent. 



Our generation has witnessed a complete reversal of the character of 

 evolutionary thinking. During the early decades of the present century, 

 after the great enthusiasm of the immediate post-Darwinian era had spent 

 itself, widespread pessimism prevailed regarding the very possibility of 

 gaining any real insight into the mechanics of evolution. This pessimism 

 was based upon many things, including a psychological reaction against 

 the unbridled and uncritical enthusiasm of post-Darwinian biologists; a 

 misconstruction of the significance of the new science of genetics; the 

 disrepute into which taxonomy had fallen; and the mutation theory of 

 the DeVries, which seemed to make Darwinian variation and selection 

 unnecessary. 



Even while this pessimism prevailed, however, its bases were being 

 destroyed by research in many apparently unrelated fields. In 1937, Dob- 

 zhansky published Genetics and the Origin of Species, in which he brought 

 together many lines of research, and demonstrated that the prospects were 

 bright indeed for understanding the mechanics of evolution in terms of 

 the genetics of natural populations. This stimulated a reassessment of the 

 relationship of many biological sciences (and some of the physical sci- 

 ences) to evolution, and the result has been a modern synthesis in which 

 all biological sciences seem to converge fruitfully upon evolution. This 

 modern synthesis has been formalized in a series of books of such im- 

 portance that any one of them would have required the revision of exist- 

 ing texts and justified the publications of new ones. Dobzhansky's book, 

 which is now in its third edition, was the first of these. It was followed in 

 1940 by Goldschmidt's Material Basis of Evolution, in 1943 by Mayr's 

 Systematics and the Origin of Species, in 1945 by Simpson's Tempo and 



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