If narcissism is one of humanity’s more stubbornly intractable traits—and it is—it’s partly because it facilitates the one basic act likelier than anything else to keep a particular physical or behavioral characteristic alive in the gene pool: breeding. Successful narcissists have a whole lot of sex, which means they’re statistically likelier to have a whole lot of babies—at least compared to everyone else. This highly adaptive component of narcissism gives it a big edge over other disorders in getting passed down to the next generation.

“When you’re talking about truly pathological narcissism, it’s hard to say why it hasn’t been eradicated from the gene pool,” says Jessica Tracy, a professor of personality and social psychology at the University of British Columbia. “But when you’re talking about the more everyday kind, it’s equally hard to see how it ever would disappear since it’s so adaptive. All you have to do is replicate yourself, and narcissists are very good at doing that.”

Male narcissists would seem to have a big advantage here, and they do. For men, breeding is biologically cheap and easy, something they could—at least when they’re young enough—do multiple times a day. Women, even if they wanted to, could never remotely keep up with that kind of fecundity. But heterosexual narcissistic males are still trying to bed women, and no matter the men’s seductiveness, women remain the more discriminating gender and will still be more selective than men about whom they bed. Even the truly narcissistic male will strike out more than he succeeds. Narcissistic women, on the other hand, have a much easier go of things simply because so many men seem almost incapable of saying no.

Psychology and human behavior students are taught early on about the famous 1978 study conducted on the Florida State University campus in which volunteer male and female subjects approached other students of the opposite sex and recited a carefully scripted proposition: “I have been noticing you around campus and I find you to be very attractive,” they said. “Would you go to bed with me tonight?”

The subjects were neither particularly unattractive nor extremely attractive—which is to say they were pretty much the kinds of partners most people do wind up going to bed with. The women’s success rate when they made this pitch was a remarkable 75 percent, though no subsequent rolls in the hay actually took place—at least not under the aegis of the study. The male volunteers succeeded with this approach precisely zero percent of the time. Remarkably, the psychologists repeated the study three more times throughout the 1980s—when the AIDS epidemic made casual sex seem like mortal folly—and about 50 percent of the men were still completely receptive to an anonymous hookup.

In the real world, this pattern holds even when the woman is manifestly bad news—narcissistically or otherwise—someone with volatile moods or a turbulent romantic or personal history. It’s not for nothing that the term “hot mess” has gained such linguistic currency, capturing as it does the Lindsay Lohans, Amanda Bynes and, at one time, the Kate Mosses of the world: Beautiful, captivating women who also, at least for a while, behave in ways that lead to their own undoing. Men can often spot this and nevertheless respond to overtures all the same. A long-ago issue of Playboy—a journal with admittedly less cred than the Journal of Psychology & Human Sexuality, in which the updates of the Florida State studies were published in 1989—included a cartoon that captured this idea splendidly. A beautiful woman in a little black cocktail dress is seated at a bar, talking to an obviously entranced man. The word “trouble” is literally written all over her, covering nearly every inch of her exposed skin. Another man stands behind the first and helpfully asks him, “Could I talk to you for a moment?” The answer, likely as not, would have been no. The entranced man had just one thing on his mind—and it didn’t involve calmly reflecting on what kind of interpersonal crack-up he was courting.

Women may react to charismatic, bad-boy men in much the way men react to bad-girl women, even if they’re not nearly the same sexual pushovers. Multiple studies have shown the seductive power of what’s evocatively known as the Dark Triad of personality traits: narcissism, impulsive thrill-seeking, and Machiavellianism—or exploitativeness. Men who score high in any of these traits—to say nothing of those who score high on all of them, which some do—also tend to exceed other men in number of sexual encounters in any given week, month or year. At a conference convened by the Human Behavior and Evolution Society in Japan in 2008, Peter Jonason of New Mexico State University, who conducted one of the studies, invoked James Bond as the perfect mash-up of all of the Dark Triad traits—and the successful sexuality that goes with it: “He’s clearly disagreeable, very extroverted, and likes trying new things—including killing people and new women,” Jonason said. The headline for the story of Jonason’s study in the UK paper The Independent was “Why Women Really Do Love Self-Obsessed Psychopaths.”

Like Tracy, the other investigators saw evolutionary value in this behavior, simply because any mating at all can result in successful breeding, launching one more little narcissist across the generational divide and into the future. “The strategy seems to have worked. We still have these traits,” Jonason said.

That, of course, raises an inevitable question: Why haven’t narcissists ultimately risen to a position of wholesale domination of the species, using their procreative prowess simply to crowd out the less dark, more agreeable majority? Jonason believes that the relative scarcity of true narcissists gives them the advantage of surprise: If most of the charming potential suitors a woman met turned out to be self-adoring, Machiavellian cads, they’d know to avoid them. But since most nice-seeming, charming guys really are nice and charming, the bad ones get to slip in under the radar.

Reprinted from THE NARCISSIST NEXT DOOR: Understanding The Monster In Your Family, In Your Office, In Your Bed—In Your World by Jeffrey Kluger by arrangement with Riverhead Books, a member of Penguin Random House Inc., Copyright (c) 2014 by Jeffrey Kluger.