In the early days of evolutionary psychology—that is, when it was just beginning to be applied to humans—I was rather critical of the endeavor, though not so much about “sociobiology”, the application of evolutionary principles to animal behavior. A lot of the early evo psych stuff on humans was weak or overly speculative.
Since then, I’ve mellowed somewhat in light of replicated research findings about human behavior that show phenomena predicted by or very consistent with the theory of evolution. Not only are the phenomena predicted and replicated, but they are in line with what other animals show. Further, researchers have also falsified some alternative explanations (“culture” or “patriarchy” is the most common one).
I’ll add here that the disturbingly common claim that evolutionary psychology is “bogus” or “worthless” as an entire field is ridiculous, both in principle and in practice. In principle, why should human behavior, or behavioral differences between the sexes, be the one area that is exempt from evolutionary influence, especially given that we evolved in small hunger-gatherer groups for at least five million years, on top of which is overlaid a thin veneer (about 20,000 years) of modern culture? That position—that all differences between men and women, say, are due to cultural influence—is an ideological and not an empirical view. If physical differences, both between sexes and among groups, are the result of evolution, why not mental ones? After all, our brain is made of cells just like our bodies!
In practice, there are several types of human behavior that, using my mental Bayes assessment, I consider likely to reflect at least some of the workings of evolution, past and present, although culture may play a role as well. There will be an upcoming paper on these fairly solid evo-psych behaviors (I’m not an author), but I’ll highlight it when it’s published.
In the meantime, we have one behavior, described in this 2017 article from Areo Magazine, that describes a “universal human behavior” involving sex differences, and a behavior that’s likely to reflect our evolutionary heritage. Although the article is four years old, it’s worth reading. The author, David P. Schmitt, has these bona fides:
David P. Schmitt, PhD, is Founding Director of the International Sexuality Description Project, a cross-cultural research collaboration involving 100s of psychologists from around the world who seek to understand how culture, personality, and gender combine to influence sexual attitudes and behaviors.
See also his Wikipedia page, which describes him as “a personality psychologist who founded the International Sexuality Description Project (ISDP). The ISDP is the largest-ever cross-cultural research study on sex and personality.”
The article, which I recommend you read, is chock-full of data. Click on the screenshot for a free read:
The behaviors Schmitt discusses in this longish but fascinating and readable piece are summarized in the first two paragraphs (there are lots of references should you want to check his claims):
Choosing to have sex with a total stranger is not something everyone would do. It probably takes a certain type of person. Quite a bit of evidence suggests, at least when it comes to eagerly having sex with strangers, it might also take being a man. Let’s look at the evidence.
Over the last few decades almost all research studies have found that men are much more eager for casual sex than women are (Oliver & Hyde, 1993; Petersen & Hyde, 2010). This is especially true when it comes to desires for short-term mating with many different sexual partners (Schmitt et al., 2003), and is even more true for wanting to have sex with complete and total strangers (Tappé et al., 2013).
Of course this is “common wisdom” in American culture: it is the heterosexual guy who does the pursuing, and does so without many criteria beyond the lust object having two X chromosomes, and he’s still often rejected, while women are far choosier about who they mate with.
There are many studies, described and cited by Schmitt (usually using lab experiments or good-looking students on campus approaching members of the opposite sex) that show the same thing. An attractive man propositioning a woman for sex is accepted about 0% of the time, while, in the opposite situation far more than half the males accept a sexual proposition from an attractive female stranger. Here are two studies, but there are more:
In a classic social psychological experiment from the 1980s, Clark and Hatfield (1989) put the idea of there being sex differences in consenting to sex with strangers to a real life test. They had experimental confederates approach college students across various campuses and ask “I’ve been noticing you around campus, I find you to be very attractive, would you go to bed with me tonight?” Around 75 percent of men agreed to have sex with a complete stranger, whereas no women (0 percent) agreed to sex with a complete stranger. In terms of effect size, this is one of the largest sex differences ever discovered in psychological science (Hyde, 2005).
Twenty years later, Hald and Høgh-Olesen (2010) largely replicated these findings in Denmark, with 59 percent of single men and 0 percent of single women agreeing to a stranger’s proposition, “Would you go to bed with me?” Interestingly, they also asked participants who were already in relationships, finding 18 percent of men and 4 percent of women currently in a relationship responded positively to the request.
This of course jibes with the behavior of many animals (in my flies, for example, males will court almost any female, even wooing pieces of dust or small blobs of wax), while females repeatedly reject males. It’s true of primates in general, and of many animal species. And it makes evolutionary sense. If a male mates with five females instead of one, he’s likely to have five times more offspring. In the reverse situation, though, a female who mates with five males in a short period will have roughly the same number of offspring as if she mated just once. That’s because she makes a huge investment in eggs and (in some species like ducks) maternal care, and so she should be selected to be choosy about her mates, looking for a male who is fit, healthy, may have good genes, and, if there’s parental care, will be an attentive father. Since the male has far less to lose, and far more to gain, by repeatedly mating with different females, this explains the strategy of “wanton male versus choosy female” sexual preference. These are likely to be evolved sexual behaviors.
This of course is a generalization. There are certainly picky men and women who are less choosy about their partners. But it’s a generalization that holds up not only in the “choice” studies I just mentioned, but in other aspects as well. Psychological studies show that (here I quote Schmitt, bolding is his)
. . . men have more positive attitudes towards casual sex than women, have more unrestricted sociosexuality than women, and generally relax their preferences in short-term mating contexts (whereas women increase selectivity, especially for sexual attractiveness.
. . . Cognitively and emotionally, men are more likely than women to have sexual fantasies involving short-term sex and multiple opposite-sex partners, men perceive more sexual interest from strangers than women, and men are less likely than women to regret short-term sex or “hook-ups.”
Considering sexual fantasies, men are much more likely than women to report having imagined sex with more than 1,000 partners in their lifetime (Ellis & Symons, 1990).
Behaviorally, men are more likely than women to be willing to pay for short-term sex with (male or female) prostitutes, men are more likely than women to enjoy sexual magazines and videos containing themes of short-term sex and sex with multiple partners, men are more likely than women to actually engage in extradyadic sex, men are more likely than women to be sexually unfaithful multiple times with different sexual partners, men are more likely than women to seek one-night stands, and men are quicker than women to consent to having sex after a very brief period of time (for citations, see Buss & Schmitt, 2011).
Here’s a table reproduced in the Areo paper taken from Buss and Schmitt (2011), where you can find the original references. Click to enlarge.
These patterns hold in nearly all studies in different parts of the world. That in itself suggests that culture may play an insignificant role in the difference I’m discussing.
Now if you’re thinking hard, you can think of at least four non-evolutionary explanations for these behaviors (I’ve combined disease and pregnancy in #3 below). Both, however, have been shown to be unlikely to be the major explanation for the sex difference in choosiness.
1.) Patriarchy: These could be cultural differences enforced by the patriarchy and socialization. Why a patriarchy exists itself may be evolutionary (e.g., males are stronger and thus can control females more easily than the other way around), but male dominance itself is not the explanation we’re testing here. Schmitt explains why (beyond observed cultural universalism), this is unlikely to explain the entire behavioral difference (all emphases are the author’s):
For instance, Schmitt (2015) found sex differences in the sociosexuality scale item “I can imagine myself being comfortable and enjoying ‘casual’ sex with different partners” were largest in nations with most egalitarian sex role socialization and greatest sociopolitical gender equity (i.e., least patriarchy, such as in Scandinavia). This is exactly the opposite of what we would expect if patriarchy and sex role socialization are the prime culprits behind sex differences in consenting to sex with strangers.
How can this be? Why are these sex differences larger in gender egalitarian Scandinavian nations? According to Sexual Strategies Theory (Buss & Schmitt 1993), among those who pursue a short-term sexual strategy, men are expected to seek larger numbers of partners than women (Schmitt et al., 2003). When women engage in short-term mating, they are expected to be more selective than men, particularly over genetic quality (Thornhill & Gangestad, 2008). As a result, when more egalitarian sex role socialization and greater sociopolitical gender equity “set free” or release men’s and women’s mating psychologies (which gendered freedom tends to do), the specific item “I enjoy casual sex with different partners” taps the release of men’s short-term mating psychology much more than it does women’s. Hence, sex differences on “I enjoy casual sex with different partners” are largest in the most gender egalitarian nations.
Overall, when looking across cultures, reducing patriarchy doesn’t make these and most other psychological sex differences go away, it makes them larger (Schmitt, 2015). So much for blaming patriarchy and sex role socialization.
2.) Fear of injury. In general, men are stronger than women (this is almost surely the result of evolution affecting competition for mates). Perhaps women are leary of accepting propositions from unknown men because they might get hurt, as do many prostitutes. But several studies show that safety alone cannot be the whole explanation:
Clark (1990) was among the first to address the issue of physical safety. He had college-aged confederates call up a personal friend on the phone and say “I have a good friend, whom I have known since childhood, coming to Tallahassee. Joan/John is a warm, sincere, trustworthy, and attractive person. Everybody likes Joan/John. About four months ago Joan/John’s five year relationship with her/his high school sweetheart dissolved. She/he is was quite depressed for several months, but during the least month Joan/John has been going out and having fun again. I promised Joan/John that she/he would have a good time here, because I have a friend who would readily like her/him. You two are just made for each other. Besides she/he has a reputation as being a fantastic lover. Would you be willing to go to bed with her/him?” Again, many more men (50%) than women (5%) were willing to have sex with a personally “vouched for” stranger. When asked, not one of the 95% of women who declined sex reported physical safety concerns were a reason why.
3.) Fear of pregnancy and/or disease. Since venereal diseases can be passed in both directions, I’m not sure that disease is a good explanation, though perhaps women are more likely to get serious disease than are men. As far as pregnancy is concerned, there’s at least one study showing it can’t be the sole factor:
Surbey and Conohan (2000) wondered whether worries of safety, pregnancy, stigma, or disease were what was holding women back from saying yes to sex with a stranger. In a “safe sex” experimental condition, they asked people “If the opportunity presented itself to have sexual intercourse with an anonymous member of the opposite sex who was as physically attractive as yourself but no more so (and who you overheard a friend describe as being a well-liked and trusted individual who would never hurt a fly), do you think that if there was no chance of forming a more durable relationship, and no risk of pregnancy, discovery, or disease, that you would do so?” On a scale of 1 (certainly not) to 4 (certainly would), very large sex differences still persisted with women (about 2.1) being much less likely to agree with a “safe sex” experience with a stranger compared to men (about 2.9).
So, sex differences in agreeing to sex with strangers are not just a matter of safety issues, pregnancy concerns, slut-shaming stigma, or disease avoidance. Controlling for all of that, researchers still find large sex differences in willingness to have sex with a stranger.
There’s a lot more in this paper, including Schmitt’s critique of the two papers cited widely as disproving the “pickiness” hypothesis. Both papers, however, suffer from extreme methodological flaws, and in both cases the results support the “pickiness” hypothesis when the flaws are corrected.
You can read the hypothesis and judge for yourselves, but I think this is one of the best examples we have of evolutionary psychology explaining a difference between men and women in behavior*. As I said, it’s shown up throughout the world in different cultures, it’s paralleled in many species of animals, alternative explanations fail to explain the data, other, unrelated data support at least a partial evolutionary basis of the choice difference, and the few papers that claim to disprove it wind up actually supporting it.
Aside from “universal” behavior like sleeping, eating, or wanting to reproduce, which are surely instilled in us by evolution (and nobody questions those), we shouldn’t ignore differences between groups, especially the sexes, as having an evolutionary origin. It’s likely that morphological differences between geographic populations, like the amount of melanin in the skin, are adaptive responses to natural selection, so why is behavior the one trait that is always off limits to evolutionary explanation? It’s ideology, Jake.
h/t: Steve Stewart-Williams
*As a reader points out below, and even more obvious evolutionary difference is that the vast majority of men are sexually attracted to women, and vice versa. That would be hard to explain as a result of the patriarchy or of socialization.