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sexual selection.
    Sexual selection has sometimes been cast as a contrast or conflict with natural selection, but such an interpretation misunderstands Darwin’s vision. Sexual selection is our most elegant confirmation of his central tenet that the struggle of individuals for reproductive success drives evolution—a notion that natural selection cannot adequately confirm because its products are also the predictions of other evolutionary theories (and also, for optimal design, of creationism itself). The proof that our world is Darwinian lies in the large set of adaptations arising only because they enhance reproductive success but otherwise both hinder organisms and harm species. Darwinian selection for reproductive success must be extraordinarily powerful if it can so often overwhelm other levels and modes of advantage.
    We may now return to the blood meal of the mating mantis. W.H. Auden once wrote, with great understanding of our lives, that love and death are the only subjects worth the attention of literature. They are indeed the foci of Darwin’s world, a universe of struggle for survival and continuity. But should they be conjoined? At first sight, nothing seems more absurd, less in keeping with any notion of order or advantage, than the sacrifice of life for a copulation. Should a male, in Darwin’s world, not survive to mate again? Not necessarily, if he is destined for a short life and unlikely to mate again in any case, and if his “precious bodily fluids” (to cite the immortal line from Dr. Strangelove ) will make a big difference in nourishing the eggs fertilized by his sperm within his erstwhile partner and current executioner.
    After all, his body is so much Darwinian baggage. It cannot be passed to the next generation; his patrimony lies, quite literally, in the DNA of his sperm. Thus, sexual cannibalism should be a premier example of why we live in a Darwinian world—a classic curiosity, an apparent absurdity, made sensible by the proposition that evolution is fundamentally about struggle among organisms for genetic continuity. But how good is the evidence? (And now I must warn you—since this essay may be the most convoluted I have ever written—that this eminently reasonable argument for Darwinism has, in my assessment, very little going for it at present. Yet an alternative interpretation, for a different reason, affirms something even more fundamental about Darwinism and about the nature of history itself. Frankly, while I’m at the confessional, I began research for this essay on the assumption that such a lovely and reasonable argument for sexual selection would hold, and found myself quite surprised at the paucity of evidence. I also steadfastly refuse to avoid a subject because it is difficult. The world is not uncomplicated, and a restriction of general writing to the clear and uncontroversial gives a false view of how science operates and how our world works.)
    A recent issue of the American Naturalist , one of America’s three leading journals of evolutionary biology, featured an article by R.E. Buskirk, C. Frohlich, and K.G. Ross, “The Natural Selection of Sexual Cannibalism” (see bibliography). They develop a mathematical model to show that willing sacrifice of life to an impregnated partner will be to a male’s Darwinian advantage if he can expect little subsequent success in mating and if the food value of his body will make a substantial difference to the successful development and rearing of his offspring. The model makes good sense, but nature will match it only if we can show that such males actively promote their own consumption. If they are trying like hell to escape after mating, and occasionally get caught and eaten by a rapacious female, then we cannot argue that sexual selection has directly promoted this strategy of ultimate sacrifice for genetic continuity.
    Buskirk, Frohlich, and Ross are frank in stating that sexual cannibalism is not only rare in general but