GENE MUTATION 



favorable ones, which must have recurred many times in the past because 

 of the high natural mutation rate, have already been incorporated into the 

 normal genotype of the species. Second, although unproven, it is gener- 

 ally accepted that a species can harmoniously incorporate into its geno- 

 type a series of small mutations more readily than it can a single, equiva- 

 lent, larger mutation. Most important, however, is the fact that subspecies 

 and closely related species generally differ from each other in a series of 

 quantitative traits, such as size, proportions, intensity of color, or extent 

 of a pigmented area. As explained above, such traits are generally in- 

 herited upon the basis of swarms of genes, each with a very small effect 

 individually. 



This theory is plausible in every detail. It has the advantage of incor- 

 porating the greater part of historical Darwinism with some of the main 

 trends of modern genetic research. It is backed up by a great body of 

 experimental data. It is hardly to be wondered at then, that this theory 

 has achieved very nearly universal acceptance. But there is another pos- 

 sibility, also based upon modern genetic research, and this will be taken 

 up in the next chapter. 



REFERENCES 



Babcock, E. B., 1947. "The Genus Crepis," Part 1, Univ. Calif. Pubis. Botany, 21, 

 1-199. This paper summarizes an extraordinarily comprehensive study of one genus, 

 with the neo-Darwinian theory providing the direction. (Turesson.) 



Blum, H. F., 1955. "Time's Arrow and Evolution," 2nd Ed., Princeton University 

 Press. The application of the laws of thermodynamics to mutation and evolution is 

 here explored. 



Clausen, Jens, 1951. "Stages in tlie Evolution of Plant Species," Cornell University 

 Press, Ithaca, N.Y. A brilliant exposition of evolution in several genera of plants, 

 from a neo-Darwinian viewpoint. ( Baur. ) 



DoBZHANSKY, Th., 1951. "Gcnetics and the Origin of Species," 3rd Ed., Columbia 

 University Press, New York, N.Y. A very readable book which is the cornerstone of 

 the neo-Darwinian theory. ( Auerbach, Demerec, Dice, Dubinin, Ives, Spencer, Stem, 

 Tschetverikoff . ) 



DoDSON, Edward O., 1956. "Genetics: the Modern Science of Heredity," W. B. Saun- 

 ders Co., Pliiladelphia, Pa. If you have enjoyed your evolution book, you might like 

 this one too. 



Morgan, Thomas Hunt, 1928. "The Theory of the Gene," 2nd Ed., Yale University 

 Press, New Haven, Conn. A classic of modem biology. ( Belling. ) 



Stabler, L. J., 1954. "The Gene," Science, 120, 811-819. A very penetrating study of 

 the theory of the gene by one of its major architects. 



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