Sleeping with the Enemy

All romance comes with some rough strife. So we try to let the petty quarrels slide, and trust our relationships will become less adversarial over time. But will they? It's looking more and more like the tensions and conflicts over commitment and fidelity and trust and jealousy are such primitive evolutionary adaptations that they are wired into our very DNA. Indeed at the genetic level men and women appear more like combatants than lovers.

This unwanted valentine comes from a relatively new branch of science called evolutionary psychology. The basic premise of evolutionary psychology is that when early humans were evolving on the savannah millions of years ago, much of their behavior was shaped by pressures to survive. Not to survive as individuals (as in staying clear of the mastodon stampede), but to survive as an ancestral lineage, which meant propagating one’s genes into the next generation. The behaviors (and attitudes) that maximized sexual “fitness” over time became ingrained in the genes themselves, and remain with us today.

We should be happy about these adaptations. They are the reason we’re here today. But what worked on the savannah doesn’t always work exactly the same way in the modern bedroom. Three University of New Mexico psychologists—Steven Gangestad, Randy Thornhill and Christine Garver-Apgar—have been studying the female menstrual cycle as an example of our Darwinian legacy gone awry. More specifically, they have been studying the way men and women’s feelings and attitudes fluctuate along with a woman’s hormonal cycle.

Ancestral women basically wanted two things in a mate: They wanted good genes, to make their offspring (and their offspring’s offspring) more fit for long-term survival, and they wanted a good partner, who would stay around to help raise the kids. But here’s the rub: Those things don’t always come in the same man, so women developed a strategy (on an unconscious level) to hedge their genetic bets. The New Mexico psychologists hypothesized that vestiges of this ancient strategy (and of men’s counter-strategy) might be seen in a modern couple’s behavior when a woman is ovulating.

Not to put too fine a point on it, they hypothesized that women tend to choose good, solid husbands to marry, but that they desire sexier men when they are most fertile. Why sexier men? Because women’s tastes in men also have ancient roots, and what we think of as sexy today equates with genetic fitness. Symmetrical build and features, good scent, deep voice, competitive personality—those traits all signal stable genes, as they did three million years ago.

The scientists have done several studies to test this idea, and the results, as reported in the journal Current Directions in Psychological Science, powerfully support the theory. For example, in four experiments women were asked to smell men’s unlaundered T-shirts: In every case the women, when they were ovulating, preferred the T-shirts of men with symmetrical features. When they were not fertile (80% of the time), they had no preference. (The scientists suspect a hormone mediates such preferences, but none has yet been identified.)

In another experiment, women watched videotapes of various men. The researchers found that fertile women prefer men who are confident, even condescending toward other men. And in yet another study, ovulating women were more attracted to creativity than to wealth. Indeed, women’s interest in traits typically associated with good life partners—financial success, kindness, intelligence, good parenting—did not fluctuate at all over their cycles. And so much for devotion: Men judged to be faithful were actually seen as less sexy by fertile women.

But hold up. Men are not just passive dupes in this mating game. If women are wired for infidelity a few days every month, then it stands to reason that men might be wired to avoid being cuckolded. And in fact that’s what the studies show: Not only are men sensitive to signals that women are ovulating (again, scent is a big cue), they also become more vigilant, proprietary and monopolizing when their wives are ovulating. It was the wives who reported both their own wandering desires and their husbands’ hovering. So one of the perverse legacies of our distant past seems to be that men are attentive precisely when women most want to be left alone with their fantasies. Perhaps future studies will reveal the gene for clueless.

For more insights into human nature, visit the Association for Psychological Science website at www.psychologicalscience.org.