Why do people have sex? The answer given by many evolutionary biologists boils down to the "selfish gene" -- the powerful propensity of DNA to replicate itself. Indeed, in this view, the impetus to transmit one's genes to the next generation underlies human (and animal) behavior in general and serves as the driving force of biological evolution. Organisms can be regarded as essentially vehicles for the transmission of genes -- and sex, or more precisely the quest to spread genes through sex, is the basic purpose of life.
Such thinking has achieved considerable influence in recent decades. It has spread from biology to fields such as anthropology and psychology, and is central to the school of thought known as sociobiology or evolutionary psychology. It is transmitted to the public via journalistic reports suggesting that genes control behavior, and by the books of eminent biologists such as Richard Dawkins (who coined the term "selfish gene") and Edward O. Wilson (who sees genetic explanations as key to achieving "consilience" or unity among fields of knowledge).
Why We Do It: Rethinking Sex and the Selfish Gene, by Niles Eldredge (published by W.W. Norton), is a valuable counterpoint to the sweeping claims made for selfish genes and evolutionary psychology. Eldredge, a biologist, paleontologist and curator at the American Museum of Natural History, presents a well-argued case against "ultra-Darwinism." (Despite his caustic use of that term, Eldredge is debating not whether evolution occurred but rather its full implications for behavior. Similarly, Eldredge and the late Stephen Jay Gould developed "punctuated equilibrium," an idea about evolution's pace that is sometimes misconstrued as an argument against evolution.)
The biological world, Eldredge argues, cannot be understood solely as a struggle for reproduction. Rather, organisms are engaged in "economic" activity as well; much of life is about finding food and, more generally, staying alive. Genes are not active competitors in a race to replicate; instead, they are snippets of information passively recording what bodily structures and functions were successful in the past in keeping organisms alive. Nor are genes the driving force of evolution; species show a high degree of stability, and evolution occurs mainly when there is major environmental change.
Gene-centered biology, in Eldredge's view, offers only limited insight into social behavior. It works well when a social system consists of organisms that are closely related, such as bees, ants and corals. But it is less successful in explaining vertebrate behavior, which involves a complex mix of economic and reproductive activity. And it is particularly unsuccessful in explaining how humans behave. Humans are capable of culture, or learned behavior, as well as genetically-based instinctual behavior, and through technology have attained a degree of insulation from Darwinian natural selection.
Moreover, humans (and, to an extent, chimpanzees and bonobos) differ from other animals in having largely decoupled sex from reproduction. People, in other words, often have sex without wanting to have babies, and engage in types of sex that could not possibly produce babies. Human sexual behavior in all its diversity, Eldredge maintains, cannot plausibly be explained as so many manifestations of the imperative to reproduce genes. Rather, sex is sometimes performed for its own sake, and is entangled with feelings of self-worth and power. Plus, sex is often connected to life's economic side. People pay for sex, sleep their way up organizational ladders, seek out partners who can provide income and wealth, and in prehistoric times probably traded sex for food.
Is economic life really a competition to spread genes? If so, one would expect there to be a strong correlation between economic and reproductive prowess. To the contrary, as Eldredge notes, wealthy individuals and nations tend to produce fewer children. And cultural norms and dictates, far from manifesting the gene-spreading impulse, often run counter to it; an extreme example is China's policy of allowing only one child per couple.
Eldredge decries the "Pleistocene cop-out" whereby evolutionary psychology assumes that behaviors must have arisen through some reproductive advantage, even if there is no such advantage today. He cites the example of rape. Is it a holdover from prehistoric times, reflecting the success rapists had in spreading their genes (and thus their genetic predisposition to rape)? This might seem plausible on the surface, but as Eldredge points out, there is little evidence to support it. Indeed, rape is evidently uncommon in hunter-gatherer tribes that survived into modern times. Rape, Eldredge suggests, has more to do with "the anomie of industrial society" than with an ineluctable urge to spread genes.
Why We Do It provides some needed skepticism not only about the supposed dominance of genes in human society, but also about claims that humanity is about to transform itself through genetic engineering. Such transformation would require not just genetically engineering a few -- or even quite a few -- individuals. Real evolutionary change means transforming entire populations and species. "The most prodigious gene-jockeying task force imaginable," Eldredge aptly notes, "could barely scratch the surface of the collective genome of six billion people."
Ken Silber writes frequently for TCS. He recently wrote about Pondering Animals.