For more than three decades evolutionary psychologists have advanced a simple theory of human sexuality: because men invest less reproductive effort in sperm than women do in eggs, men's and women's brains have been shaped differently by evolution. As a result, men are eager for sex whereas women are relatively choosy. But a steady stream of recent evidence suggests this paradigm could be in need of a makeover.

"The science is now getting to a point where there is good data to question some of the assumptions of evolutionary psychology," says social psychologist Wendy Wood of the University of Southern California (U.S.C.).

The eager males–choosy females paradigm doesn't imply that men and women literally make conscious decisions about how much effort they should put into short- and long-term mating relative to their costs of reproduction—minutes versus months. Instead the idea is that during human history, men and women who happened to have the right biochemical makeup to be easy and choosy, respectively, would leave more offspring than their counterparts.

In 1993 psychologists David Buss and David Schmitt, then at the University of Michigan at Ann Arbor, used that idea to generate a series of predictions about men's and women's sexual behavior. As part of their study, Buss and Schmitt surveyed college students about their desire for short- and long-term mates (that is, one-night stands versus marriage partners), their ideal number of mates, how long they would have to know someone before being willing to have sex, and what standards a one-night stand would have to meet. In all categories the men opted for more sex than the women.

Although the study has been cited some 1,200 times, according to Google Scholar, there were "huge gaps from what I'm used to as a scientist," says Lynn Carol Miller of U.S.C. Miller says that in order to evaluate the relative proportion of mating effort devoted to short- and long-term mating in the two sexes, the proper method is to use a scale such as time or money, which has the same interval between units, not the seven-point rating scale that Buss and Schmitt used.

In a study to be published in the journal Sex Roles: A Journal of Research, Miller and her colleagues carried out their own version of Buss and Schmitt's work, asking how much time and money college students spent in a typical week pursuing short-, intermediate- or long-term relationships. The proportion of mating effort dedicated to short-term mating was the same for men and women. Similarly, both men and women showed an equivalent tendency to lower their standards for sex partners, and men did not report feeling constrained to have far fewer sexual partners than they truly desired.

"I'd certainly accepted the idea that men pursue purely sexual relationships with greater fervor than women do," says Paul Eastwick of the Texas A&M University in College Station. "This is the first time I've seen data that makes me think, 'Hmm, I wonder if that sex difference isn't so robust.'" Miller says the results are to be expected if paternal investment boosted the survival rate of offspring during our species' 200,000-year history. If both sexes invest in their offspring's survival, she says, they should both show similar mating adaptations.

As a corollary to male eagerness for sex, men are also supposed to be bothered more by sexual infidelity than emotional infidelity, because men have a vested interest in making sure their offspring are their own and not another man's. Surveys have indeed found that in the U.S. and several other industrialized countries more men than women express greater concern with sexual infidelity than with emotional infidelity (falling in love with someone else). But another recent study suggests jealousy patterns could have something to do with glitches in people's ability to form secure relationships.

Psychologists Kenneth Levy and Kristen Kelly of The Pennsylvania State University surveyed 416 undergraduates to see which type of jealousy bothered them more. They also assessed the students' so-called attachment styles. Previous studies had found that more men than women have what's called a "dismissing avoidant" style in relationships, meaning they tend to deny their emotions and their need for the other person.

When Levy and Kelly broke down their jealousy results by attachment style, they found that men and women who had secure attachment styles were both more likely to view emotional infidelity as more upsetting than a sexual affair. Men with the dismissing style were more bothered by sexual infidelity, but women who manifested this style were also, although the effect was more pronounced in the males.

Levy says attachment styles are largely determined by early experiences with caregivers—usually mom and dad. To explain why more men than women exhibit the dismissive style, he says, "we would have to hypothesize that men are more likely to be raised in such a way that would promote dismissive attachment."

Beyond simply poking holes in the standard evolutionary psychology narrative, researchers have another paradigm ready to put in its place: U.S.C.'s Wood and Alice Eagly of Northwestern University propose that men and women adapt their outlooks to fit their society's division of labor between the sexes, which results from physical differences in size, strength and mobility (during pregnancy).

In a 2009 study Eagly, along with Eastwick and another colleague asked college students of both sexes to imagine themselves as either a future homemaker or provider. Students who imagined being homemakers rated their anticipated spouse's provider qualities as more important than that spouse's homemaker qualities. The finding fits with data indicating that women and men who earn more are more likely to get married, suggesting they make more attractive partners.

"In more equal actual roles, men and women have more similar mate preferences," Eagly says. "In very different marital roles that confine women to a domestic role, men and women choose differently."

The evidence, however, does not move Buss, now at the University of Texas at Austin. He calls Eagly and Wood's theory "bizarre" for positing that "natural selection has shaped sex differences in male and female bodies, but not in male and female brains and the psychological adaptations those brains contain."

In Wood's view the traditional evolutionary psychology paradigm was attractive because it explained the pattern of sex differences people saw around them in a way that made those differences seem natural. It assumed that men and women have always interacted in the way they do now. "We would say that men and women have evolved to act in a lot of different ways," Wood says. "We're the ultimate flexible species."

28 Comments

1. 1. silvrhairdevil 04:15 PM 10/14/10

   "...the idea is that during human history, men and women who happened to have the right biochemical makeup to be easy and choosy, respectively, would leave more offspring than their counterparts."
   
   In actuality, those who conquered the most territory and had the most wives & concubines left the most descendants:
   
   Giocangga - 1.5 million,
   Genghis Khan - 16 million,
   "Niall of the Nine Hostages" - 3 million,
   Charlemagne - 600 million,
   Etc.

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2. 2. BoolySpark 04:43 PM 10/14/10

   I agree with Buss and the bizarre description. Even more so that this will be published.

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3. 3. hotblack 05:09 PM 10/14/10

   Funny, I always looked at it as simple supply/demand. As soon as enough individuals of one sex wanted it more than the other, the sex who appeared to want it less would realize they have a commodity, and make everyone else miserable holding it over each others heads.
   
   ...which I maintain still describes most of human social behavior. What tipped that balance, could have been social, physical, or any combination, but, there it is.
   
   It's interesting how different people are toward you when they learn that you don't value them sexually, or are trying to outcompete them for someone elses mating rights.
   
   Stupid, primitive species.

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4. 4. wildthing 05:29 PM 10/14/10

   I think perhaps the respressive sexual social environment interferes too much to make any determinations... as conscious being we could chose to have several patners and share child rearing among a set of adults for maximum security financially and emotionally and have a very flexible parent child ratio for population regulation and could do much better at maintaining a home and nuturing chldren versus the over stressed toxic nuclear family of over consumption..so why don't we??

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5. 5. scribblerlarry 06:08 PM 10/14/10

   I am always stunned by "scientists" who compare AMERICAN men and women then go on to generalize about "men and women" as though those raised in the US are suitable representatives of the human race. I have live in countries where their "work" wouldn't even be necessary - it is understood by everyone in the society that that women's and men's interest in short term sex, mid term sex/relationship, and long term sex/relationship are similar.

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6. 6. blindboy 07:09 PM 10/14/10

   This isn't science it is guess work. The number of environmental variables with the potential to influence reproductive behaviour is simply too large. The genetic components of the behaviour are simply swamped. Scribblerlarry draws attention to one of these variables but there are many others ranging from embryonic influences, to diet, age, previous relationship history and so on and so forth.

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7. 7. jtdwyer 08:17 PM 10/14/10

   More than just a sample population of Americans, this is some very specific sample group comprised of university students, aged ~18-22(?), primarily from some specific region of the U.S. but likely also including a significant percentage of non-U.S. citizens, possibly including a large number of Asian nationals, etc., etc.
   
   Drawing general conclusions about ultra-modern human attitudes about sex from this extreme sample is absurd!
   
   Perhaps an identical study should be conducted among airline employees, construction workers, hospital staff, the homeless, etc. Surely conclusions drawn from analyses of these special populations would be just as valid when extrapolated to the entire human population.
   
   The social science community in particular need to seriously pursue some kind of minimal standard procedures for producing studies and meaningful conclusions. They should now be the butts of jokes.

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8. 8. ectopist 03:44 AM 10/15/10

   Interesting and thanks for that, but please could you unpack the concept of "emotional infidelity"? I find it highly contestable!

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9. 9. gazmend.selimi@gmail.com 07:10 AM 10/15/10

   Human genes, through the generations passes through both: men and women bodies,...continuously, therefore theory "the natural selection has shaped sex differences in male and female bodies, but not in male and female brains and the psychological adaptations those brains contain." is not 'bizarre'.
   

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10. 10. mankinirevolution 11:05 AM 10/15/10

    The problem I have with many studies on the differences between the sexes is that they often have misleading pitfalls. These pitfalls oftentimes lead us to believe there are greater differences between the sexes then what probably are. A couple articles that address this notion are on the Mankini Revolution website. One is called the top ten ways gender studies can be misleading, and another asking if gender studies are accurate.

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11. 11. mankinirevolution 12:06 PM 10/15/10

    At mankini revolution there's an article that lists 10 ways research studies on gender can be misleading. Personally I believe many studies on gender fall prey to such bias. This, in turn with the media, has propelled misconceptions about the sexes. The reality is males and females are much more alike then what's traditionally thought.

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12. 12. mankinirevolution 12:07 PM 10/15/10

    Interesting article. I'm a big fan of all scientific american magazines.

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13. 13. minkelj 05:45 PM 10/15/10

    For anyone who feels like the old evolutionary psychology paradigm got short shrift, check out David Buss's response to my article: http://fistfulofscience.com/2010/10/15/david-buss-defends-evolved-sex-differences-exclusive

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14. 14. Wayne Williamson 06:16 PM 10/15/10

    Interesting article...I think that with the move to more parity between males and females(except in repressive societies) and the reduced pressure to procreate...things have changed considerably over the last 50/100 years...Interesting to see how we adapt...

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15. 15. Abduction in reply to silvrhairdevil 07:30 PM 10/15/10

    Comment #1: Your comment doesn't contradict the assertion you believe it to at all, indeed you give evidence that that male lust unrestrained by female choice is drastically asymmetric (due to minutes to conceive (and having no guarantee of genetic fatherhood) vs 9 months and guaranteed genetic motherhood). And even if there were a contradiction Ghenghis khan etc. are not on an evolutionary timescale nor is their's a pragmatic or genetically encodable strategy.
    
    I suppose you were being deliberately idiotic and ironic.
    
    comment #3 said 'Stupid, primative species': Yes we are primates, highly cultured cavemen, to call us as a species stupid is a little strange though, considering our brains are the most complex adaptive structures in the known universe.

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16. 16. martineden 07:38 PM 10/15/10

    Sounds like a politically correct study.

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17. 17. Abduction 07:51 PM 10/15/10

    comment #14: Don't conflate 50/100 years with evolutionary timescale, I don't see why the fact that we decouple sex from procreation, (contraception, IVF), should bear upon our hardcoded preferences for mates.
    
    Frome the article- "Miller says the results are to be expected if paternal investment boosted the survival rate of offspring during our species' 200,000-year history. If both sexes invest in their offspring's survival, she says, they should both show similar mating adaptations." No because mens' genes would be more frequent if the men invested the relatively small amount of effort in cuckholding, whereas woman could gain less from being promiscuous.

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18. 18. Wayne Williamson 08:56 PM 10/15/10

    Abduction...interesting comments...let me summarize your objections....
    
    not that i agree with any of the posters but here i go...wee....
    
    #1(silvrhairdevil) states the obvious...the number of offspring correlates to genetic fitness....for 99 percent of our existence this is correct...
    
    #3(hotblack)just pointing out that a lot(if not most people) are stuck with the roots we came from;-)..name your favorite topic...war...politics...etc...
    
    #14(me)trying to state that the sexes are more equal now than at any time in the past...not that there is parity yet....also, the world has too many people to support in the long run(or short run if you watch the news..famine..flood..pick your favorite disaster)
    
    

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19. 19. zstansfi 02:18 AM 10/16/10

    Give me a break. This study presents one of the best explanations for why I got out of Psychology. There are confounds all over the place! For one, why should time and money be such accurate measures of reproductive effort? Did the authors even consider the effect of changing sexual mores? And here's the kicker: this survey was based upon college students! Psychologists have been berated about the problems of studying such a homogeneous population, and yet time and again they make sweeping claims based upon an unrepresentative sample. Not to mention that the original study in '93 was conducted at Ann Arbor, with a student population which was likely less interested in obtaining sex than the population currently inhabiting USC.
    
    Miller calls herself a "scientist", my God.

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20. 20. davidschmitt 11:10 AM 10/16/10

    This article contains mischaracterizations of current evolutionary psychological thinking on sex differences in sexuality.
    First, Sexual Strategies Theory (Buss & Schmitt, 1993) did not claim that all men are “easy” short-term maters and all women are “choosy” long-term maters. To the contrary, the key contribution of Sexual Strategies Theory to psychological science was to highlight the differences within men when pursuing short-term mates versus long-term mates and within women when pursuing short-term mates versus long-term mates. Subsequent to this development within evolutionary psychology, several additional theories (e.g., Strategic Pluralism Theory, Life History Theory, Attachment Theory) have been elaborated and extended to accommodate this important advance in adaptationist thinking. Current evolutionary thinking continues to focus on the mating psychology differences within men and within women, as well as highlighting fundamental differences between the genders. It seems only ill-informed researchers who have failed to read the massive literature in the area and the ideologically-driven critics of evolutionary psychology continue to depict the “easy men” versus “choosy women” straw man. This does nothing but hurt psychological science.
    Second, Sexual Strategies Theory did predict that the adaptive psychological design of how men pursue short-term mates will be, in some ways, different from the adaptive design of how women pursue short-term mates. Important design feature differences include the restrictiveness of who, when, and how many short-term sexual partners men and women are likely to desire. However, contrary to the limited tests put forth as examples in the article, these design feature differences have been validated in literally dozens of ways using thousands of participants across hundreds of cultures. This includes meta-analyses of sexual attitudes, cross-cultural studies of romantic desires, and field experiments of sexual behaviors (for a review, see Schmitt et al., 2003 [http://www.bradley.edu/academics/las/psy/facstaff/schmitt/documents/schmitt.etal.2003.jpsp.pdf]).
    In summary, Scientific American should know better than to fall for the scientific canard of “easy men” and “choosy women.” Such characterizations should be, and I hope will be, beneath us all.
    

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21. 21. davidschmitt 11:12 AM 10/16/10

    Also, perhaps the foremost topic currently within short-term mating research from an evolutionary perspective is the sexual desire shifts observed within women across the ovulatory cycle. As women’s short-term psychology is activated, they appear to express more restrictive desires for genetic traits in men that would benefit short-term seeking women. Modern evolutionary psychology views women as heavily designed for seeking short-term mates (in some ways even more specially-designed than men!), but it is clear that their short-term mate seeking psychology does not have the same design as men’s. The extant literature on this view is substantial [http://www.oup.com/us/catalog/general/subject/LifeSciences/EvolutionaryBiology/?view=usa&ci=9780195340990].
    

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22. 22. blechten 01:00 PM 10/16/10

    This article displays a very annoying error. People confuse ultimate cause with proximate cause constantly. As humans evolved into what we are today, the concept of cheap sperm versus an expensive egg makes sense and when viewed in the rest of the animal kingdom is also bears out. Now, when viewed in terms of modern humans with everything that we carry with us from all our evolution, it may not make sense. That doesn't mean it was true from an evolutionary perspective, it just means it is not an evolutionary driver any more and could, in fact, mutate away over time without evolutionary consequence.
    
    People need to keep in mind the time frames being discussed when dealing with evolution.

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23. 23. Wayne Williamson in reply to davidschmitt 02:56 PM 10/16/10

    thanks for the link...very informative study...also kind of restrictive as mostly targeting college students...still nice..

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24. 24. Bea_maria in reply to wildthing 07:14 AM 10/17/10

    Isn't that bordering on being a cult???

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25. 25. figleaf 10:46 AM 10/17/10

    @Davidschmidt #20: I'm gratified to hear that actual lower-case evolutionary psychologists have more nuanced theory than... 99% of all popular accounts thereof let on.
    
    But if that's true then Miller's work should hardly be threatening at all: her work seems only to threaten established perceptions routinely promoted by ideology-driven *adherents* of the one-dimensional promiscuous-men/particular-women model articulated ad nauseum in the popular press.
    
    Indeed, if as you say non-pop professional EP is confined by adherence to a single straw-mannish model of sexual selection then by putting pressure on that model Miller ought to be giving real EPs an opportunity to present the more subtle, more sophisticated, and more accurate Sexual Strategies Theory you're endorsing.
    
    Because, seriously Dude, out here in the real world we're not hearing a lot about those, m'kay? Now's your chance. Why waste it attacking that line of research when you could instead co-opt it as confirming your more sophisticated readings against the distortions introduced by ill-informed but highly-enthusiastic ideologues who keep misappropriating the work real EPs?
    
    Because it's not like progressives have a monopoly on "political correctness." And in the case of EP it's the ideological adherents who seem to be doing more damage to the actual work than are its equally ideological antagonists.
    
    Finally, even if Miller's work threatened to undermine all of your Sexual Strategies Theory I still don't see how that should produce so much agitated cheek-puffing (e.g. "Miller calls herself a 'scientist,' my God!") There really are huge numbers of confounding factors! Much of the observable behavior attributed to *sexual* adaptation really could be *general* adaptation that's been unevenly expressed by culture-induced behavioral artifacts. I mean, if it's difficult to accept many of the ham-fisted claims of early sociobiology and pop-evolutionary psychology it's inconceivable that human behavior has no selected-for components. Or even sexually selected-for components. To the extent Miller and other social scientists help distinguish what isn't adaptive sexual behavior the more confident we can all be that what remains is.
    
    What possible problem could conscientious scientists have with that?
    
    figleaf

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26. 26. aforsy in reply to silvrhairdevil 06:18 PM 10/17/10

    Those are outliers.

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27. 27. jtdwyer in reply to davidschmitt 02:56 AM 10/18/10

    Your point of view is quite interesting, but the extant to which the literature you refer to shares the view to which you refer, apparently based on the expert opinions of the authors, does not substantiate your views as might scientific studies of specific human sexual behaviors rather than those applied generally to human female sexuality.
    
    For example, the subject of this report has been restricted to the study of male and female students at just a few universities, mostly between the ages of about 18-22 years of age, with results, by extension, representing all modern humanity.
    
    In my limited observations of female humans of all ages, I've found that their sexual behavior not only varies significantly according to socioeconomic standing but by age of maturity, as female physiological sexual development occurs over a period of at least 30 years.
    
    To quote some other book referred to in an ad at the location you referenced; "A breakthrough in our understanding of life on this planet and throughout the universe." I agree wholeheartedly...

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28. 28. myartman 03:14 PM 10/25/10

    asking college students about their long-term plans for relationships and partnerships is begging for skewed data. a disappointing approach to what might otherwise be a fruitful question.

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