Sunday New York Times, June 20, 2004


'Why We Do It': Sex and the Single Cell


Published: June 20, 2004

BIRDS do it. Sullen teenagers sneak around to do it. Even biologists think about doing it, though it puzzles them. The problem is that sex has its costs. If women reproduced by giving birth asexually, like aphids, to exact genetic duplicates, any beneficial mutations occurring in the mother would pass to all of her offspring. But in sexual reproduction, since newborns share but half the mother's genes, only half of her children would probably reap the genetic advantage. Sex seems a bad idea, evolutionarily speaking. It's a puzzle, then, why our ancestors -- those one-celled creatures thriving in ancient seas -- ever bothered to try it.



In ''Why We Do It,'' the eminent paleontologist Niles Eldredge, of the American Museum of Natural History, takes up the problem. His goal in this accessible book, however, is not so much to solve the puzzle as to discover the purpose of life, which for him is not sex. He takes his stand against scientists who adhere to the theory of the selfish gene and, more generally, the doctrines of sociobiology and evolutionary psychology. They (prominently, Richard Dawkins and E. O. Wilson) maintain that most of life's activities are ultimately aimed at procuring a sex partner for the propagation of one's genes.


Like Darwin, with whom he declares his allegiance, Eldredge pursues a quasi-teleological investigation of the main objective of life. In ''The Origin of Species,'' Darwin proposed that the struggle for existence, which involved much suffering and death, yielded the most exalted object we were capable of conceiving -- namely, ''the production of the higher animals.'' Eldredge, though, regards the purpose of life to be neither the generation of the higher animals nor the spread of one's genes; rather, it's economics. This may sound like an echo from the halls of the University of Chicago -- and Eldredge does slide in that direction. But he initially suggests a more comprehensive meaning for economics.


He defines economics as energy transfer and flow throughout an ecological system. On African savannas elephants consume huge quantities of grasses, absorbing the energy to carry on their physiological processes, including the production of large piles of dung, which dung beetles reprocess into soil nutrients, which feed plants on which elephants graze. All organisms live in intersecting ecological systems through which energy flows and is transformed. Eldredge glides from this abstract notion to a somewhat more concrete meaning of economics when he declares that in Darwin's conception, the struggle for existence indicated the effort to secure energy resources -- food -- not the attempt to produce offspring. (Contemporary evolutionists frequently recruit Darwin to their side and, often as not, bend him into unlikely positions.) Eldredge does allow that with most animals, the effort to get food ultimately serves the aim of reproduction; but with human beings, he contends, sex has been shorn of its baby-making function.


He describes those mundane varieties of human sexuality that have scant reproductive outcome: masturbation, homosexuality, contraceptive coitus, pornography, rape, sex slavery and theme parks of the teenage imagination. He considers these now to be the predominant modes of human sexual activity. Moreover, we have evidence that economics controls sexual reproduction, not the reverse. The rich, demographers have shown, are different from the rest of us: they generally have fewer offspring. Such examples demonstrate, Eldredge believes, that our getting and spending lay waste to the sociobiological assumption that all human activities have the ultimate evolutionary goal of spreading successful genes to the next generation. For him sex is merely a fraction of the currency flow consolidating a community.


If sex no longer has the primary purpose of spreading successful genes and thus furthering evolution of the species, what is it good for? Eldredge says the real reason for sex is its function in producing stable species that are more resistant to extinction than colonies of simple, asexual organisms. His logic, never explicitly stated, seems to be that when the superficial procreative function of sex is conceptually demoted, the real significance of sex will be revealed. He sees bonobo chimpanzees, our closest living relatives, as illustrating its stabilizing and unifying power. Their rampant sexual gymnastics, with both the same and different sexes, and with astounding frequency, do seem to effect social bonding throughout a local community. Yet comparable behavior in human communities, as many utopian experiments testify, would quite likely have the opposite result: disintegration. Also, Eldredge offers no evidence that sexual species are more resistant to extinction than bacteria -- after all, blue-green algae have been around since the beginning. Even if sexual behavior has become partly decoupled from its procreative function -- though only in human societies -- this development alone hardly supplies a reason to believe it has deeper, species-unifying features.


THE hidden lever by which Eldredge attempts to lift his argument to plausibility is the highly controverted notion of species selection, which is natural selection applied at the species level. For this argument to work, a species must itself have the character of an individual, as opposed to that of a mere collection of individuals. And the trait selected -- sexuality -- would have to benefit that individual (in this case a species) in competition with other individual species lacking the trait. But do sexual species compete with bacteria for resources or to produce more daughter species? Only the speculative imagination might hazard an answer to this question, and Eldredge doesn't even try. And while the frenzied flow of energy coursing through New York clubs might suggest otherwise, neither our species nor any other sexual species seems to possess the structure of a coherently unified individual, so that selection could act upon it. A more vigorous and explicit metaphysics would be needed to make the idea of species as unit of selection spring to life.


Contemporary science has cast aside many veils from the sexual dance, but a few yet remain to sustain the mystery.


Robert J. Richards, a professor of the history and philosophy of science at the University of Chicago, is the author of ''The Romantic Conception of Life: Science and Philosophy in the Age of Goethe.''

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