Ask a straight man, “How do you like your women?” and it’s unlikely he’ll answer, “Dumb and sleepy.” But according to new findings, these characteristics—and any other traits suggesting that the lady isn’t particularly alert—are precisely what the human male has evolved to look for in a one-night-stand.

In an article soon to be published in Evolution and Human Behavior, University of Texas–Austin graduate student Cari Goetz and her colleagues explored what they called the sexual exploitability hypothesis. The hypothesis is based on the differences between male and female reproductive strategies as humans evolved. For ancestral women, casual intercourse with an emotionally unattached man who had no clear intention of sticking around to raise any resulting offspring constituted a massive genetic gamble. By contrast, for a man with somewhere around 85 million sperm cells churned out every day—per testicle—the frivolous expenditure of gametes was far less detrimental to his genetic interests. Goetz and her team began with the assumption that—because our brains evolved long before prophylactics entered the picture—female cognition is still sensitive to the pregnancy-related consequences of uncommitted sex and women remain more reluctant than men to engage in it. They set out to test the idea that any indication that a woman’s guard is lowered—that she’s “sexually exploitable”—is a turn-on for your average man. “[T]he assessment of a woman’s immediate vulnerability,” surmise the authors, “may be central to the activation of psychological mechanisms related to sexual exploitation.”

This is an inflammatory hypothesis, of course, and the language employed in the field doesn’t help matters. It’s worth noting that in the evolutionary psychology sense, the word exploitable simply means that a woman is willing or can be more easily pressured into having sex—which takes her own desires, rather disturbingly, out of the equation. Even if she’s the aggressor, a prostitute, or a certifiable nymphomaniac, having casual sex with her would still constitute “exploiting” her (or at least her body), according to this model.

So how did this team put their sexual “exploitability” hypothesis to the test? Goetz and her colleagues planned to call a bunch of undergraduate males into the lab and ask them to rate a set of women in terms of attractiveness based on their photographs. But first they needed to pick the appropriate images. To figure out which sorts of women might be deemed most receptive to a sexual advance or most vulnerable to male pressure or coercion, they asked a large group of students (103 men and 91 women) to nominate some “specific actions, cues, body postures, attitudes, and personality characteristics” that might indicate receptivity or vulnerability. These could be psychological in nature (e.g., signs of low self-esteem, low intelligence, or recklessness), or they might be more contextual (e.g., fatigue, intoxication, separation from family and friends). A third category includes signs that the woman is physically weak, and thus more easily overpowered by a male (e.g., she’s slow-footed or small in stature). According to the authors, rape constitutes one extreme end of the “exploitation” spectrum—cheesy pickup lines the other.

By asking students for the relevant cues, the experimenters reasoned, they’d keep their own ideas about what makes a woman “exploitable” from coloring their study. When all was said and done, the regular folks in the lab had come up with a list of 88 signs that—in their expert undergraduate opinions—a woman might be an especially good target for a man who wanted to score. Here’s a sampling of what they came up with: “lip lick/bite,” “over-shoulder look,” “sleepy,” “intoxicated,” “tight clothing,” “fat,” “short,” “unintelligent,” “punk,” “attention-seeking,” and “touching breast.”

Next, Goetz and her colleagues searched the Internet for publicly available images of women displaying each of these 88 cues. Once they had pictures of women licking their lips, partying, circling their areolas, and all the rest, they cross-checked them with a separate group of students who surmised that—at least in their subjective views—the images indeed matched the cues. The specific coding details aren’t provided, unfortunately, but presumably these independent raters just used their best guesses to determine what an “attention-seeking” or “unintelligent” woman looked like.

Now it was time for the test. A fresh group of 76 male participants was presented with these images in a randomized sequence and asked what they thought of each woman’s overall attractiveness, how easy it would be to “exploit” her using a variety of tactics (everything from seduction to physical force), and her appeal to them as either a short-term or a long-term partner. The results were mixed. Physical cues of vulnerability—the pictures of, say, short women and hefty ones—had no effect. These women were not necessarily seen as easy lays, nor were they judged as especially appealing partners for either a casual fling or a lifelong marriage. On the other hand, the more psychological and contextual cues—pictures of dimwitted- or immature-seeming women, for example, or of women who looked sleepy or intoxicated, did seem to have an effect: Not surprisingly, men rated them as being easy to bed. But more importantly, they were also perceived as being more physically attractive than female peers who seemed more lucid or quick-witted. This perceived attractiveness effect flipped completely when the participants were asked to judge these women as potential long-term partners. In other words, the woozy ladies were seen as sexy and desirable—but only for fleeting venereal meetings. They lost their luster entirely when the men were asked to rate these same women’s attractiveness as prospective girlfriends or wives. The possible evolutionary logic behind this interaction is fairly straightforward: In the latter case, the man would risk becoming the cuckoldee, not the cuckolder. (Of course you could also argue that men might rather marry a woman who looked like she could hold up her end of the conversation over French toast.)

In a follow-up study (that ended up being published first), the authors tried to add some nuance to their sexual exploitability hypothesis. Graduate student David Lewis led a project to narrow in on the specific type of man who would be most alert to the sort of “exploitability” cues outlined above. Not every man, it seems, is equally proficient at homing in on these weak spots in women. So he and his colleagues asked 72 straight men to evaluate the same photos as before, and in the same way. But this time, the researchers also measured some key personality traits in the male raters, as well as the extent to which they desired and pursued uncommitted sex. The students were asked, for instance: “With how many different partners have you had sexual intercourse without having interest in a long-term committed relationship with that person,” and, “How often do you experience sexual arousal when you are in contact with someone you are not in a committed romantic relationship with?”

The main finding to emerge from this follow-up study was that the more promiscuity-minded men who happened also to have deficiencies in personal empathy and warmth were the ones most vigilant and responsive to female “exploitability” cues. Men without this critical calculus—say, a disagreeable man who prefers monogamy, or a caring one who likes to play the field—are more likely to have these cues fly right past their heads and miss the opportunity to capitalize on an “easy lay.” So rather than the sexual exploitability hypothesis summing up the male brain as one big ball of undifferentiated stereotype, the caveat here is that there are multiple subtypes of reproductive strategies in men. Not all men are pricks, in other words.

It’s easy to see the sexual exploitability hypothesis as misogynistic, but I don’t believe the authors are advancing a chauvinistic ideology. Take those kinds of complaints up with natural selection, not the theorists untangling its sometimes-wicked ways. The authors are trying—admirably, I think—to decipher an implicit social algorithm in the hopes of better understanding gender relations.

Having said that, the studies to date are also far from perfect. There’s the obvious criticism that ancestral women didn’t have mojitos and martinis to loosen their tenuous hold on chastity, and so ethanol-fueled conceptions couldn’t have exerted any kind of selection pressure. Yet knowing evolutionary psychologists, the equally obvious countercriticism is that modern women’s inebriation is just an exaggerated version of altered states of consciousness that human beings have indeed experienced for hundreds of thousands of years. More important are methodological concerns.

For example, given that the photos of women were collected online, confounds are inevitable. Do photos of boozed-up young women posted on the Internet simply happen to depict more physically attractive females—ones who’ve dolled themselves up for parties, say—than the sober head shots of those who party less? It’s hard to believe that this would be the same for all the “exploitability” cues (such as “sleepy”) but the same problems would certainly apply to cues such as “tight clothes” and “come hither look.” To control for things like facial symmetry, it would have been better, in my opinion, to have the same model exhibiting a targeted sampling of the 88 cues generated by the original raters.

It also seems to me that although men may lower their standards when it comes to judging women for casual sex, even the creepiest, horniest, coldest man has his aesthetic limits. This could be why the proposed physical signs of “exploitability” —say, being obese or a dwarf—didn’t pan out in the first study. According to a strict interpretation of the authors’ model, after all, a woman with even profound mental handicaps (such as being comatose while on life support or having an IQ commensurate with that of a sickly possum) would make her pretty damn hot. That just doesn’t ring true. I’m going out on a limb here, but from their evolutionary theoretical perspective, perhaps some minimal degree of genetic normalcy or maternal competence, even in “easy” women, is key. According to their model, given that the unconscious goal for these males is to spread their genes without being tethered to paternal responsibilities, even the most incapacitated of women should, at the very least, have enough brain cells firing to raise a healthy child to the age of maturity.

I think it’s fair to say that the findings are consistent with the authors’ sexual exploitability hypothesis—and evolved sex differences in reproductive strategies more generally. But here we run into one of the consistent criticisms of evolutionary psychology, which is that there can be a “just-so story” to explain every data set. Perhaps the effects reported by Goetz and her team can be interpreted just as well from a non-evolutionary perspective. (If you think so, I’d be curious to hear your ideas in the comments section below.) However you interpret them, results like these can feel self-evident, given that “obviously” men would find drunk and air-headed women easy to screw. But we also must be on the lookout for our own retrospective biases: After all, I’m not so sure most people would have predicted that men would also find such women more attractive. All else being equal, would you really have thought that the average man would subjectively perceive such women to be physically more alluring than their sober, bright-minded peers?