The Biology of Love—Not

A stripper who feels sexy gives a more tip-worthy lap dance than one who feels uncomfortable or bloated.

All in all, it was probably a mistake to let scientists anywhere near the topics of love and lust. Just as analyzing a joke kills it, so analyzing why we fall in love with those we do was bound to end badly. Consider the idea that aging professors attract their nubile young female students because young women are genetically programmed to fall for high-status, well-off men. Further, aging men are supposedly wired to be attracted to fertile young things.

Result: when our fiftysomething married man beds his student, the fault, dear Brutus, lies not in his stars or his character or his moral compass but in his DNA.

It's no wonder reductionist explanations for behavior—especially "my genes made me do it"—are so popular: they let us off the hook. Bad choice in whom you went home with that night? Understandable; you were overwhelmed by his pheromones. Unfaithful? Not your fault; blame the genes that program men to spread their seed widely. Except that in many cases more mundane explanations that invoke plain old thinking and feeling, rather than an unconscious drive to get your genes into the next generation, are more plausible.

Take the lap-dance experiment. Last year, scientists asked 18 strippers to log how many hours they worked, what they earned in tips and whether they were ovulating, menstruating or neither. While ovulating, the phase in the monthly cycle when a woman is most likely to conceive, the strippers earned an average of $335 per five-hour shift, compared with $185 while menstruating. The reason, the (male) scientists concluded, is that a fertile woman emits a signal that she is physiologically ripe to conceive. Men are, supposedly, genetically programmed to detect the signal—since being drawn to a fertile woman is something evolution and natural selection would favor—and to behave in a way (generous tipping) that might win her.

Leaving aside the fantasy element of that last part, this explanation has some problems. First, there is no good evidence that men can detect pheromones, hormones or any other magic molecule that reveals when a woman is ovulating. Also, even if such magic molecules existed, there is a simpler explanation for why men give bigger tips to ovulating strippers, one with no need to invoke unconscious genetic impulses. Women feel sexiest when ovulating. Just a guess, but maybe a stripper who feels sexy gives a more tip-worthy lap dance than one who feels uncomfortable during her period. If so, says David Buller of Northern Illinois University, author of a 2005 book, "Adapting Minds," which questions evolutionary explanations for complex behavior, "the lap dance may be [more alluring to] the client, so he will tip more."

In a similar explanatory vein, women in several studies say their husbands or lovers are more attentive and amorous when they are ovulating. This, too, is supposed to reflect men's ability, honed by natural selection, to detect signals (pheromones, hormones, whatever) that indicate when sex is likely to yield children. Children are how evolution keeps score; genes for behaviors that produce offspring—in this case, for detecting a woman's fertile period—survive the brutal winnowing process of natural selection. But again there is a simpler explanation for why men turn on the charm when their partners are ovulating, and it harks back to the strippers. Ovulation increases libido. A libidinous wife is more likely to send signals—readers are invited to provide their own examples—that she would welcome affection. Again, no genes controlling us like puppets. A loving heart and working brain are enough.

Men's taste in women is also supposed to reflect evolutionary selection, and to show that genes have our behaviors and preferences on a short leash. Specifically, men prefer D cups and broad hips, says this school of thought, because those are signs of fertility. A man who picks fecund females is more likely to leave offspring—that measure of evolutionary success—than a man who is attracted to reproductive duds. Two problems here. There is no empirical evidence that women whose shape deviates from the Barbie "ideal" are less fertile. Also, different societies at different times have idolized very different female bodies. The Rubenesque woman is nothing like the 2008 ideal of, say, Angelina Jolie. Genes do not evolve fast enough to account for that change in male tastes. Some esthetic preferences, including in a mate, are driven by culture, not DNA.

When an Anna Nicole Smith (27) marries a J. Howard Marshall (89), much of the public nods knowingly and figures, DNA programs women to seek out older, wealthy men, and men to go for young, fertile babes. Please. Give the lady credit for rationally evaluating the benefits of marrying an incontinent octogenarian multimillionaire. Besides, when 50-year-old men are asked the age of their preferred mate, most settle on 40 or so, not 25, even though the younger woman is more fertile. And on average, 25-year-old women say their ideal guy is 28, even though a 50-year-old is more likely to have the status and 401(k) that evolutionary explanations say women are programmed to lust for. This Valentine's Day, let's celebrate all the ways our hearts and minds, not our mindless DNA, guide us in the ways of love.