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C H A P T E R 5 A Science of Rare Males The Genetics of Populations in the Long 1960s One aspect of sexual selection, in the original Darwinian sense, is the evolution of secondary sexual characters. Another even more important aspect is the reproductive isolation between species by sexual selection. From an evolutionary point of view, sexual isolation is the chief function of sexual selection, that is to say, of sexual discrimination. There is a third important function of sexual selection, viz. the maintenance of genetic heterogeneity in populations as a consequence of the advantage of heterozygotes in sexual selection. —Ernst Bösiger, “Role of Sexual Selection,” 1974 In 1946, a young French scientist named Claudine Petit entered graduate school at the Centre National de la Recherche Scientifique (CNRS) in Paris. For her dissertation research, she decided to investigate selection sexuelle in the fruit fly Drosophila melanogaster. She published a series of articles throughout the 1950s, including her description of a “rare-male” mating advantage in Drosophila. Females, she argued, preferred to mate with exotic males; this tendency illustrated true female choice, because it could not be explained by variations in the vigor of male courtship. This story is remarkable for any number of reasons. Petit articulated a vision of female choice in insects that assumed female flies possessed the cognitive apparatus necessary for choosing; Petit is a woman; and she is French. Why was choice-based behavior in flies so surprising? Following the Second World War, the numbers of biologists studying populations of Drosophila had steadily increased. The population geneticists who studied Drosophila sought to understand how genetic differences spread in a population, rather than investigating the causes, effects, and heredity of mutations in individual development as had the “classical” geneticists trained by Thomas Hunt Morgan. In the genetic analysis A Science of Rare Males 109 of populations, the small, black-bellied fruit flies acted as human equivalents, as stand-ins for you and me. At the same time, population geneticists capitalized on the association between insect minds and instinctual mechanization. Although fruit flies were not social insects (as exemplified by the self-sacrifice of ants or bees for the good of the nest/hive), insects generally represented an evolutionary path to instinctual sociality that acted as a foil for the cultural basis of human sociality. Flies seemed to lack the cerebral or intellectual capacity to learn, and so population geneticists came to depend on flies for their ability to behave naturally in the most unnatural of conditions, including being raised by the hundreds in small glass vials filled with a gelatinized mixture of yeast, unsulfured molasses, and agar. Because of the obvious differences between insects and people, fruit flies offered a way for geneticists to investigate the process of evolution without overt eugenic overtones. Yet the similarities in the genetic structure of human and insect populations allowed these same biologists to generalize from their results on fly evolution to probable mechanisms of evolution in humans. Petit’s description of “rare-male” mating preferences in female fruit flies did not sit easily within this framework in which fruit flies mated mechanically and humans chose their mates. Petit’s research was also unusual because she is French. Most biologists in France before the Second World War were reluctant to adopt Mendelian genetics. Petit’s advisor was a notable exception, and his work on genetic diversity of fruit fly populations formed one of the few French programs studying population genetics in the 1940s. After completing her dissertation research, Petit formed connections with the population genetics community in the United States, especially with the help of Theodosius Dobzhansky. Her influence on the population genetics community, therefore, arose from her international ties to American geneticists rather than domestic ties to biologists in France. When Petit began her research, there were very few female population geneticists in charge of their own laboratories. Yet the number of women interested in sexual selection research in fruit flies at this time was larger than one might expect —two! Petit formed a long-lasting collaboration with another woman working in population genetics, Lee Ehrman. They met when Ehrman was a graduate student in Dobzhansky’s laboratory and shared many research interests—among them, female choice. In interviews, Petit and Ehrman each insisted that their early interest in female choice had nothing to do with the fact that they were women; female choice was simply an open question that...

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