Let’s talk about sex (at dawn)

Anthony Weiner is an idiot. I think we can at least all agree that if you’re going to use a social networking site to spread illicit photos of yourself, you damn well better learn the difference between direct messaging and displaying your crotch to all of your followers. That said, all of us are idiots sometimes. And if I had to put money on it, I’d wager dollars to donuts that the thing we are the most stupid about is sex. But why?

What’s the point of sex? You may think I’m the idiot for asking the question – the answer is obvious, right? Well…

The answer to why humans have sex turns out to be a more complicated than you might think. Obviously, reproduction is one reason. But compare how many times you’ve had sex and how many children you have. Clearly, there must be something else going on. What about, “We have sex because it feels good.” But why does it feel good? If your answer is “So that we’ll have sex,”

It’s not that science never asks questions about sex. It’s just that a lot of the studies are bad, and a lot are weighed down by prejudice, squeamishness or both.

By way of example: Most people believe there is a difference between men and women regarding attitudes towards sex. Men are more promiscuous, and women are more selective. The standard explanation for this is as follows:

Men must invest relatively little time and resources to potential offspring, so having sex with as many partners as possible increases potential progeny without much cost. However, men can not be sure of paternity once a woman gets pregnant. Women, on the other hand, must invest huge amounts of time and resources in each child, but they can know that the child is theirs. This led to something called the “Sexual Strategies Theory,” in which men and women have evolved different attitudes and behaviors towards sex that will maximize their evolutionary fitness (the number of children they produce that go on to have children of their own). Leaving aside the assumption that sex is only about reproduction, a lot of the “science” that purports to support this theory is circumstantial at best.

Take one of the best known examples: At a college campus, an attractive female grad student would approach random men and say, “I’ve been noticing you around campus and find you very attractive. Would you go to bed with me tonight?” Most of the men said yes. When an attractive male graduate student asked the same of random women, most of them declined. Using this data, researchers concluded that this supported sexual strategies theory – men are promiscuous and women are selective, because they’ve evolved to maximize reproductive success. Never mind the rampant casual sex that occurs on college campuses, or the increased danger women face in casual sexual encounters. The data fits the theory, so the theory must be right (for the best demolition of this theory, check out this post about a follow-up study – it’s long but fantastic)

But what if the theory is wrong? What if even the underlying assumptions about human sexuality are wrong? That is the premise of Sex at Dawn: The Prehistoric Origins of Modern Sexuality by the husband and wife team of Christopher Ryan and Cacilda Jethá.

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The major thesis of the book is that humans did not evolve to be in long-term, sexually monogamous relationships. Far from it, Ryan and Jethá conclude that pre-agrarian human societies were exceedingly promiscuous. Drawing on archeological, behavioral and anatomical evidence, as well as analysis of extant pre-agrarian human societies and our closest primate relatives, the authors build an argument with page after page of clear, convincing and often humorous discussion.

The book is not for the sexually repressed though. It was a little unsettling to read lengthy treatises on the size of primate testicles on the bus, but these authors clearly know their stuff, and know how to build their case. Speaking of testicle size, here’s the argument in a nutshell: It turns out humans have huge huevos. Maybe not squirrel huge (NSFW), but still pretty big compared to related species. Large testicles in animals usually points to sperm competition. Sperm competition usually means that females mate with multiple males. Bonobos and chimps, our closest primate relatives and profligate polygamists, also have sizable scrotums. Bonobos have bigger balls (and more sex) while chimps’ are slightly smaller. By contrast, gorillas have tiny testes – but male gorillas enforce their primacy by physically preventing other males from mating with their harem. Male gorillas have enormous muscles, so their sperm don’t need to do as much work.

If giant gonads isn’t enough to sway you, there’s plenty more where that came from. My favorite aspect of this book is the extensive critiques of the science that supports human monogamy. For example, when looking for evidence of monogamous primates, scientists that want to uphold the standard view often turn to gibbons. Ryan and Jethá point out that our last common ancestor with gibbons was over 20 million years ago (as opposed to 6 million years for chimps and bonobos), gibbons rarely have sex unless it will lead to pregnancy, they don’t live in social communities and of course, they have small testicles. They also cite lots of studies on primitive human cultures that appear to be monogamous, but upon closer scrutiny are anything but. There’s a culture in the amazon that supposedly has “marriage,” but in order to “divorce” and remarry, a woman just has to hang her hammock in another man’s hut. Another supposedly monogamous tribe has hunting ceremonies where men are required to chose a mate other than their wife, and if the chosen woman’s husband objects, he’s ostracized.

There’s much more, but I fear I can’t do it justice. Unfortunately, since I’m not trained as an anthropologist, I can’t be certain that the authors aren’t cherry-picking examples that support their conclusions. Thomas MacAulay Millar, who blogs at Yes Means Yes (and wrote the amazing critique of the sexual strategies theory research I mentioned above) is a bit more circumspect:

My take was that they did a wonderful job of undermining the arguments that pair-bonding, chimp-focused folks make, but a less good job actually making an affirmative case.

He notes that, as with most evo psych research, they’re almost entirely dependent on circumstantial evidence. To me, it seems like a lot of evidence, and the weight of it all makes it more compelling. But maybe I just want to be persuaded. Besides that, Millar notes:

Christopher Ryan makes little attempt to hide that he’s writing a brief for polyamory, so read him essentially as a polyvangelist, if you know what I mean.

Fair enough, but I definitely recommend you read him just the same.

Comments

  1. #1 Rosie Redfield
    June 17, 2011

    Our Popular Science Book Club read it. It’s an amusing read, but there’s way too much cherry-picking and unjustified extrapolation for it to be taken as serious science.

  2. #2 John
    June 17, 2011

    Nice article, really sounds interesting. But you need a grammar checker please! Two glaring ones: site -> cite and theres -> theirs.

    [Fixed, thanks! -KB]

  3. #3 Kevin
    June 17, 2011

    @ Rosie – Yeah, I read it as more of an effort to shift the paradigm of thought rather than an attempt at the last word on the subject. Seems like there’s a lot of cherry-picking and unjustified extrapolation in the whole field of evo psych, so I thought it was refreshing to see them attack it from so many angles.

  4. #4 Alan M.
    June 17, 2011

    > Christopher Ryan makes little attempt to
    > hide that he’s writing a brief for polyamory,

    Actually, I believe he never heard of polyamory until the book was nearly finished, when he ran across an article about filmmaker Terisa Greenan and her group (poly spokespeople). The word only occurs briefly near the end of the last chapter, as an afterthought; see the index.

    He and Cacilda have been at pains to say they have no prescription to offer for how modern people should deal with their supposedly promiscuous evolved nature, other than to understand that it’s there. This despite the pressure they got from their publisher (HarperCollins) to turn Sex at Dawn into a prescriptive helf-help guide to promote sales.

    Nevertheless, it has certainly gotten a lot of notice in the poly world, which has long had to deal with the public assumption that polyamory is *contrary* to human nature.

    Alan M.
    Polyamory in the News
    http://polyinthemedia.blogspot.com

  5. #5 Kevin
    June 17, 2011

    @ Alan M. – Thanks for the clarification.

  6. #6 Thomas MacAulay Millar
    June 17, 2011

    I don’t have the book handy, but my recollection of the intro is that it’s difficult not to read it as prescriptive. They essentially say that monogamy has doomed humans to war with natural instinct. Whatever denial they make about prescribing a remedy, they’re saying that monogamy is unnatural.

    One can simply say that deriving any “ought” from an “is” is a logical fallacy, but people who say that are usually issuing a boilerplate denial on their way to making a sweeping claim about human nature that ends in an express or implied “ought”.

    Here’s what he said at CNN.com (here http://www.cnn.com/2010/OPINION/07/27/ryan.promiscuity.normal/index.html):

    “Few mainstream therapists would contemplate trying to persuade a gay man or lesbian to “grow up, get real, and stop being gay.” But most insist that long-term sexual monogamy is “normal,” while the curiosity and novelty-seeking inherent in human sexuality are signs of pathology. Thus, couples are led to believe that waning sexual passion in enduring marriages or sexual interest in anyone but their partner portend a failed relationship, when in reality these things often signify nothing more than that we are Homo sapiens.

    This is a problem because there is no reason to believe monogamy comes naturally to human beings. In fact, for millions of years, evolutionary forces have cultivated human libido to the point where ours is arguably the most sexual species on Earth. ”

    Whether Ryan had a grounding in the terminology before the book is interesting but not dispositive. He is pretty clearly arguing that the social position of monogamy as a hegemonic arrangement is destructive and that its replacement with some kind or kinds of nonmonogamy is preferable. Any claim that he has no opinion on how we should live is inconsistent with his writings.

    That’s not to say I disagree. I’m poly-friendly and was polyamorous until my current relationship, so I’m not arguing for hegemonic monogamy, just pointing out that Ryan has a strong opinion.

  7. #7 Sven DiMilo
    June 17, 2011

    I think we can at least all agree that if you’re going to use a social networking site to spread elicit photos of yourself, you damn well better learn the difference between direct messaging and displaying your crotch to all of your followers.

    I think we can at least all agree that if you’re going to use a publicly-viewed science-blogging site to spread your opinions by writing in English, you damn well better learn the difference between ‘elicit’ and ‘illicit’. FFS.

    [I actually disagree, but fixed anyway :-) -KB]

  8. #8 abb3w
    June 17, 2011

    Thjomas MacAulay Millar: Whatever denial they make about prescribing a remedy, they’re saying that monogamy is unnatural.

    So is not whacking that annoying SOB next to you with a rock, as are many other aspects of civilization.

    Confusing “natural” with “good” is a textbook fallacy, known as the “Appeal to Nature”, and related to Hume’s is-ought problem. Non-monogamy is an instinct; what we ought to do about that instinct is a separate question. It may be that we ought to work out mechanisms to indulge it, such as the current tendency in the US to serial monogamy; it may be that we ought to pretend that it isn’t there, so it’s seldom indulged and frowned on when it is.

    Of course, it may be that the authors are relying on how common it is for people to erroneously apply the Appeal to Nature in their own reasoning. My impression, however, is that the Appeal to Nature is more commonly used as a post-facto rationalization than a prior justification.

  9. #9 Thomas MacAulay Millar
    June 17, 2011

    Abb3w, I understand, but I do not think that Ryan is merely describing. By invoking the ex-gay analogy, I think he’s pretty clearly making the fallacious argument from nature himself, because while it is a logical fallacy, it has powerful rhetorical appeal. That’s why I say heand his co-author have written a brief for polyamory.

  10. #10 informania
    June 17, 2011

    “for the best demolition of this theory, check out this post”

    Sexual strategy theory and this so called pleasure theory do not seem incompatible to me at all.
    You are familiar with the distiction between ultimate and proximate causes for behavior, are you not? At least you do not seem to be…

  11. #11 Kevin
    June 17, 2011

    @ informania – It’s entirely possible that I’m missing something in either SST or the pleasure theory that would make them compatible, but the way I read it, they have different underlying assumptions. SST seems to imply that a) sex is only for reproduction in humans and b) men and women have completely different motivations/strategies for having sex and choosing a partner. I originally read that article at the same time I was reading Sex at Dawn, so it’s possible I conflated the two arguments, but it seems to me that if human sexuality evolved in the context of social bonding, that would invalidate a lot of the underlying assumptions of SST

    In addition, the women in the study I mentioned were not less likely to have sex with a stranger because he was unfit/unattractive/unlikely to provide resources to offspring as SST would predict. They were less likely because of the inherent danger women face in that context.

    Or I may be missing something entirely.

  12. #12 informania
    June 17, 2011

    Let me explain more clearly..

    Questions of behavior can be of an ultimate or a proximate nature (As described by Niko Tinbergen)
    One can question the mechanistic cause and life-time development of a behavioral trait; so called proximate behavioral causes. Or one can question the road of its evolution and adaptative function.

    These four different types of questions yield different answers, but these do not adres the same aspect of a behaviour and are thus not mutually exclusive per se.

    SSH tries to explain sexual behavior on the basis of fitness payoffs and parental investment criteria, and is in fact an ultimate causation hypothesis.

    The question of pleasurability clearly addresses the mechanistic cause of sexual behavior. But even if it was addressed in an ultimate sense it would not exclude SSH;
    i.e. Pleasure in sex might have developed within a population of organisms that only copulated by chance. Pleasure leading to active seeking, promoting copulation above chance and thus spreading the pleasure mechanism within the population essentially turning your circular argument into a positive evolutionary feedback loop.

    SSH basically suposes that the investing sex should benefit from being choosy (if it is able to, of course), this is in no way upset by pleasurability of copulation.

  13. #13 informania
    June 17, 2011

    “the women in the study I mentioned were not less likely to have sex with a stranger because he was unfit/unattractive/unlikely to provide resources to offspring as SST would predict.”

    Only if you think of fitness judgement on a high cognitive level.
    This can not just be inferred, for mechanisms for judging or choosiness
    are quite probably simple affective heuristics.

  14. #14 informania
    June 17, 2011

    On social bonding in humans I’d advice Primeval Kinship by Bernard Chapais, a 2008 book from Harvard University Press.

    I usually don’t do commercials, but it might clarify on the subject matter at hand.

  15. #15 Mike Olson
    June 18, 2011

    1. Love that circular reasoning logo.
    2. Concern over spelling errors can generally be resolved by reading for context, rather than as a grammarian.
    a) Eats shoots and leaves…Eats, shoots and leaves, obviously have different meanings but can be resolved if subject matter is understood. Panda or hitman?
    3. I tend to believe that in regards to human psychology, sociology and philosophy, those proposing the theory tend to voice theories that largely reflect their own desires, beliefs and predispositions.
    a) The only theories that seem to really make sense are those that acknowledge a basic difference in the thinking and behavior of each individual.
    b) To simplify, what is right for you, may not be right for me and even given those two differences, you can still find other humans who are comfortable with none of several proposed options.
    4. I found the comparison of testicular size interesting in that Human size/ratio fell somewhere between gorrillas-with their harems and bonobos with their multiple partner, bisexual approach. In short gorrillas fight other males, get as many females as possible but have the smallest nuts. Bonobos on the otherhand will have sex with pretty near any other available bonobo and they have the largest stones. Humans, so I had read, fall somewhere in the middle. I tend to believe that reflects a more monogamous behavior on the part of both genders. But, that is my personal philosophy prior to being exposed to the research/info/correlation and after.

  16. #16 Kevin
    June 18, 2011

    @ Mike – re: 2) Thanks for the support :-)

    re: 4) Actually, humans fall between chimps and bonobos, and both species are promiscuous maters (though chimps less than bonobos. By contrast, gorillas have REALLY tiny balls compared to all 3 of the others, especially if you do a testis size/body size ratio.

  17. #17 Mike Olson
    June 18, 2011

    Thanks for the clarification. Obviously, humans don’t have a mating season per se, and humans will engage in a variety of behaviors that have little to do with procreation, but much to do with sexual gratification, is the same true with these other primates? This whole subject gets interesting to me because it seems as though other animals have intelligence at levels previously considered to be more anthromorphic than reality. In the case of chimps I watched a PBS special which discussed that they have a notion of justice and fair play. Beyond that, the show seemed to give the impression that their thought process was very similar to humans but with incredible issues with delaying gratification. There are also dogs which are said to be as nearly as intelligent as five year old children. It all kind of comes together in a philosophic murk for me in that I’m given a notion of 2-5 year old humans with adult sexuality issues…with both the dogs, dolphins and these primates. Again, for me, this isn’t a major area of interest, but different bits of flotsam and jetsam I’ve been exposed to which create a vague picture at best and leaves me wildly open to speculation…thanx!

  18. #18 muhr
    June 19, 2011

    “Actually, humans fall between chimps and bonobos”

    can you direct me to where you read this? i was under the impression that the common chimp and bonobo both have a higher testes weight to body weight ratio and larger testes.

    and while testes size seems to be the focus when talking about what might be the human mating system, testes size is only one feature that sperm competition acts upon. There’s also the midpiece volume of sperm (indicates mitochondrial density), sem g1 and g2 (encodes for coagulating proteins), penis length (humans contrary to widespread claims aren’t exceptionally long), penile morphology, and many other things.

    add it all up and humans do appear to have had sperm competition, but nothing like that seen in multi-male/multi-female mating systems such as the bonobo or common chimp. the amount of sperm competition in humans doesn’t seem inconsistent with polygamy or monogamy along with some extra pair copulations on the side.

  19. #19 muhr
    June 19, 2011

    i’m specifically referring to polygyny where i wrote polygamy.

  20. #20 Kevin
    June 19, 2011

    @ muhr – I believe I read that in Sex at Dawn, though I did not go back and double check, so I may be misremembering. The book is heavily annotated, so if I can find the spot where they talk about it, I’m sure they cite the primary source.

  21. #21 CST
    June 29, 2011

    Actually, humans fall between chimps and bonobos

    gibbons rarely have sex unless it will lead to pregnancy, they don’t live in social communities and of course, they have small testicles

    From a comment at Primate Diaries Zinjanthropus’s calculations (based on Alan Dixson’s data) of testes:body size ratio are:

    1:373 in Chimps
    1:1000 in Gibbons
    1:1266 for Humans
    1:2114 in Orangs
    1:3280 in Gorillas

    Unfortunately, since I’m not trained as an anthropologist

    The authors aren’t trained as anthropologists either. Nor zoologists nor primatologists nor linguists (I counted three pseudo-Whorfian arguments in the book)…

    No, I’m not a fan of the book. Too much negativity. The topic is interesting, though. As an alternative, I’d suggest the chapter “The Optimal Number of Fathers” in Sarah Hrdy’s Mother Nature. Supplement that with Shackelford & Goetz’s paper “Adaptation to Sperm Competition in Humans” and you’ve covered at least 80% of the meat of this book with none of the sarcasm or snide comments.

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