GENETIC DIVERGENCE UNDER UNIFORM SELECTION. I. SIMILARITY AMONG POPULATIONS OF DROSOPHILA MELANOGASTER IN THEIR RESPONSES TO ARTIFICIAL SELECTION FOR MODIFIERS OF ci D

The fossil record contains examples of striking parallels in the evolution of closely related taxa. These episodes of parallel evolution generally have been interpreted as the product of very similar selection pressures acting on closely related lineages. But parallel evolution has never been construed to be an allele-forallele identity of response among lineages; it has long been realized that identical selection pressures do not guarantee identical responses to selection (Gulick, 1872; Wright, 1931). Indeed, conspecific populations of numerous species of animals and plants have diverged under similar selection pressures for a large variety of physiological, biochemical, and morphological characters (reviewed in Cohan, 1984). For instance, different populations of the spider mite Tetranychus urticae have responded to selection for organophosphate resistance by alternative mechanisms: a New York population has responded by detoxifying the poison, while a European population has altered its neural sensitivity to organophosphates (Matsumura and Voss, 1964). Other examples include diverse responses to selection for heavy metal tolerance among different mine populations of Mimulus guttatus (Macnair, 1976), multiple responses to selection for malaria resistance among different populations of Homo sapiens (Luzzatto and Testa, 1978; Luzzatto, 1979), and many more.