Inducing death in the mother of your future children may not be the wisest way to maximize your contributions to the gene pool. And yet male flies do just that: their sperm (or, more correctly, their seminal fluid) increases the death rate of recipient females. In the November 21 Proceedings of the National Academy of Sciences, Civetta and Clark suggest that the polygamous nature of fly society provides an explanation for this puzzling behavior. They find that male flies that induce a greater mortality effect (killing off their mates more rapidly) are also the most successful in inducing females to produce sons and daughters from their sperm, rather than from the sperm of competing males who come along later (Proc Natl Acad Sci USA 2000, 97:13162-13165). Thus the mother's early death is the cost of ensuring more sons and daughters for the first husband.

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