The Evolutionary Dynamics of Complex Polymorphisms,,

The theory of balanced polymorphism which has been elaborated by population geneticists, notably Sewall Wright and R. A. Fisher, has in the main been concerned with the effects of single loci. As theory generally goes apace with experiment, this accent on single locus polymorphisms has been due to the plethora of observational evidence relating to simple cases. It is sufficient to note the vast effort made by Dobzhansky and his co-workers in their elucidation of the inversion polymorphism of the third chromosome of Drosophila pseudoobscura. In recent years, however, a few cases have come to light of polymorphisms involving more than one Mendelian unit. Among these are the inversions on different chromosomes found in D. robustca studied by Levitan (1955 and 1958), the shell color of Cepaea nemoralis reported by Lamotte (1951) and by Cain and Sheppard (1952), the complex mimicry pattern in certain butterflies (Sheppard, 1959) and the inversions in two chromosomes of the grasshopper Moraba scurra analyzed by White (1957) and Lewontin and White (1960). The study of effects of natural selection on single locus polymorphisms must take into account only inter-allelic effects such as additivity and dominance. In multi-locus polymorphisms, however,