The evolution of sexual dimorphism in humans: Part 2

In a post one week ago, “The ideological opposition to biological truth,” I argued that sexual dimorphism for body size (difference between men and women) in humans is most likely explained by sexual selection, and that it also reflects behavioral differences between males and females: males compete for females, and greater size and strength give males an advantage. That competition results from females—in many species, not just ours—being a “scarce” resource for males, since the number of males capable of breeding far exceeds the number of females who cannot breed because they’re tending offspring or in gestation. This disparity can be categorized in two ways:

  • The behavioral operational sex ratio: the ratio of sexually active males to fertilizable females at a given time. This is about 11.7 in humans!
  • The physiological operational sex ratio, the same ratio but for all individuals capable of reproducing (rather than those actually engaged in mate-hunting). This is about 8.6 in humans.

The ratios are greater in some primates (gorillas have values of about 84!), but if they’re greater than 1, there’s room for sexual selection, since there are more males seeking females than there are females available as mates. This itself is one bit of evidence for the operation of sexual selection in humans.

Now how the sexual selection actually operated in our ancestors is not perfectly clear. Some of it, as the data suggest, involves male-male competition: fights between males to control females, as we witness in gorillas, deer, and elephant seals. Females are more or less constrained to mate with the winning males. Or females may prefer to mate with the biggest and strongest males, for those males may protect their offspring—and hence the female’s genes—better than do smaller, weaker males. (This gives an evolutionary advantage to those females who can discern and choose the best males.)

Both of these factors can, of course, work at the same time, and there are other more arcane forms of sexual selection I won’t mention, including other signs in males of “good genes”. But any sexual-selection scenario goes along with a difference in sexual behavior, explaining why, even today, males are more promiscuous and willing to mate than are the choosier females.

A further possibility is that there could be an ecological distinction between males and females, with males hunting, and thus needing size and strength, while females do gathering (presumably females don’t have time to hunt because they’re rearing children). That doesn’t involve sexual selection, but it also fails to explain all the data, like the correlation between sexual dimorphism and polygyny within humans, and the fact that in our primate relatives there’s not only the same correlation among species, but no palpable division of labor among males and females. It also doesn’t explain the existence of traits like beards, lower voices, or same-sex aggression among human males but not females. Nevertheless, there’s no reason why several forces couldn’t work together to cause men to have evolved larger body size and increased musculature (as well as other features) in our ancestors. But surely sexual selection is one, for the evidence below fits no other hypothesis.

As I noted, these relatively uncontroversial ideas about sexual selection (not mine, actually; they’re the conventional wisdom among evolutionists beginning with Darwin), was challenged by Holly Dunsworth, an associate professor of anthropology at the University of Rhode Island, on her website. Dunsworth, who called my theory (supported by lots of data cited in my original post) a “story”, offers her own speculations, which really are a story because they lack empirical support and don’t explain a lot of observations. Here’s what she said:

It’s not that Jerry Coyne’s facts aren’t necessarily facts, or whatever. It’s that this point of view is too simple and is obviously biased toward some stories, ignoring others. And this particular one he shares in this post has been the same old story for a long long time.

What about the other side of the body size sexual dimorphism story?

What about the women?

Selection could well be the reason they stop growing before men and why they end up having smaller bodies than men, on average.

Perhaps men can make babies while growing, but perhaps women can’t. Energetically, metabolically. So reproduction wins over growth. We reach sexual maturity and stop growing. Is that just a coincidence?

Why doesn’t this (and other tales) fit alongside the big-aggressive-males-take-all explanation for sexual dimorphism? #evolution

But as I noted in the piece she criticized, selection on females—through either evolution of female preference or on differential ecological roles between the sexes—could affect sexual dimorphism. But Dunsworth conveniently ignored that bit. Her criticisms were echoed by an article by Jesse Singal in New York Magazine, which claimed, as did Dunsworth, that I was offering mere “stories”—unevidenced speculation. Singal said this:

In Dunsworth’s view, all she is asking for is some nuance and, well, skepticism. “People love to boil complex processes down to their preferred (intentional or not) story,” she wrote, “with some in leading roles and others completely absent, and we don’t have to take that anymore.” Her tweeted example about growth nicely captures this: It could be that Coyne’s aggressiveness story leaves out important details about why men are bigger than women, or fails to explain certain aspects about that differences. Overall, it certainly seems like people are quicker to latch onto evo-psych stories that reinforce certain views of men and women.

That last sentence is a veiled accusation that my piece was sexist. I reject that completely.

As I noted in part I of this response, neither Singal nor Dunsworth appreciated that I have a long published history of criticizing “just-so” stories in evolutionary psychology. I don’t like unevidenced speculation when it’s promoted as truth. But the sexual selection theory for human sexual dimorphism is supported by a lot of evidence. It is manifestly not a mere “just-so” story.  In my original piece I adduced this evidence (revised slightly):

  • In human societies studied by Richard Alexander, those societies that are more polygynous (in which males compete more intensively for females) show greater sexual size dimorphism than societies that are more monogamous. This was a prediction made before the data were acquired—a prediction derived from sexual selection theory. And it was fulfilled. UPDATE: I see now that Alexander’s finding wasn’t reproduced in another experiment, so consider this conclusion questionable.
  • Among species of primates, there’s a good correlation between the polygyny of a species and sexual dimorphism: those species in which males have a higher variance in offspring number, and in which males thus compete more intensely for females, also show a greater ratio of male/female body size, even when corrected for phylogeny. (Too, in primate species in which males fight each other over females, the relative size of the canine teeth, used in battle, is larger than in species showing less direct male-male competition.)
  • In humans, as in many other species in which males compete for females, the sex ratio at birth favors males. They then die off at a higher rate due to higher risk-taking and exploratory behavior, and also senesce faster, which is why among older humans there are so many more females than males. (Check out any Gray Line tourbus.) This is predicted by sexual selction theory.
  • In line with the above, in humans and other primates, males show from the outset great exploratory and risk-taking behaviors, and as adults show many other behaviors that differ from those of females, such as greater dispersal. Is this due to the Primate Patriarchy? Probably not, given that these differences in behavior are shown in many species besides ours and make evolutionary sense.

There’s more evidence, too, which I’ll mention shortly.

But what’s the evidence for Dunsworth’s theory? As far as I can see, there isn’t any. Her theory claims that 1) females can’t reproduce while growing, while males can. 2) There’s a tradeoff between growth and reproduction, so if you stop growing as a female, you can start reproducing earlier. Conclusion: females stop growing before males because reproduction is all-important, and therefore they’re smaller than males as adults.

But the data don’t even support her theory. Puberty begins in females at about ages 10 and 11, and in males between 11 and 12.  (The age of both appears to be decreasing in recent years.) Yet males keep growing this whole period and well beyond, as do females. There’s no indication that females stop growing when they become reproductively competent. Here are growth curves (stature and weight) for both males and females. Stature begins tapering off at about ages 14-15 in both sexes (a slower taper in males), but both sexes continue to grow until age 20.




Now we don’t know about body sizes and ages of puberty in our ancestors, which is the really important information, and I doubt we’ll have that given that it’s virtually impossible to ascertain the age of puberty in fossils. But clearly there’s no support in any data for Dunsworth’s hypothesis that “perhaps men can make babies while growing, but perhaps women can’t. Energetically, metabolically.” Both men and women can make babies while they’re still growing. But men continue to grow not only faster but also bit longer than do women (see above), something which explains sexual dimorphism. But since men are reproductively competent when they hit puberty, why do they keep getting bigger? Dunsworth doesn’t tell us, but sexual selection theory does. Men achieve greater stature and muscle mass by both growing faster than females, and tapering off a bit later.

So Dunsworth’s hypothesis is not only unsupported by data, but fails to explain the growth data that do exist.

More important, her theory doesn’t explain the four points given above—points that are well explained by sexual selection theory.  She and New York Magazine fail to realize that the sexual-selection explanation for human sexual dimorphism is not a “story”, but makes supported predictions and clarifies previously obscure observations. How irritating to see these people distort what we know about evolutionary theory and human biology!

As I mentioned in earlier posts, I think Dunsworth is blinkered by her ideology, because she thinks that sexual selection theory ignores females. Well, straight male-male competition without female choice does involve evolution mainly in males, but there are forms of sexual selection that involve female choice, too, and that has surely happened in species like birds and fish. In those groups, and others, males show ornaments and colors not useful in male-male competition, but are the object of female choice. And some of that process may have happened in our own lineage. The competing theories are not zero-sum, so that only one can be right. All these processes can work together. But surely one is sexual selection.

Regardless, sexual selection as an explanation implies that there are also sexual differences in behavior: differences we see in modern experiments and are probably not purely cultural because a. they’re predicted by the differences in body size and b. we see the same difference in mate choosiness in many other species—and not just primates. It’s an ineluctable consequence of the difference in reproductive investment between males and females.

I’ll now list some other observations about human mating and morphology that are explained by sexual selection theory but not explained at all by Dunsworth’s theory. Some of these come from the references given at the bottom of the post.

  • In other sexually dimorphic primates, including chimpanzees and gorillas, direct contests between males can be observed, and probably existed in our ancestors since paleoanthropological data show that many more males were killed by violence than females, possibly reflecting inter-group battles, which in modern hunter-gatherer societies are often over females. Many societies also show “bride theft”, capture of females by bands of males—common in Amazonian hunter-gatherer societies.
  • Male humans have more robust skulls than do females, including mandibles and brow ridges. This may reflect evolution to withstand blows to the head. (Males also have a higher tolerance for pain.)
  • Men are not only taller and heavier than women, but are stronger, particularly in the upper body. While size differences are about 8%, and body mass about 15-20%, women’s bodies have a higher percentage of fat, so that when you look at fat-free body mass, men are 40% heavier, have 60% more lean muscle mass, 80% greater arm muscle mass, 75% more upper-body muscle mass, and 50% more lower body mass. This difference in relative amount of muscle mass cannot be explained by Dunsworth’s theory, which is purely about growth, but is explained by male-male competition under sexual selection—and perhaps by female preference as well. This is reflected in differential athletic performance, and is why men and women usually compete separately in athletics. Even for men and women of equal sizes, men are far stronger; as Hill et al. note, “the average man is stronger than 99.9% of women (some of this, of course, may be because men work out; I haven’t checked the references.)
  • In every society studied, men are physically more aggressive than women, both in play as kids and as adults. The vast majority of murderers are men, and this aggressive activity peaks during men’s peak reproductive years, when they would be competing for mates most strongly. These data do not include killings in war.
  • Traits like beards and lower voices in men (men’s vocal folds are 60% longer than women’s, giving them lower voices) have been shown to act as indicators of dominance; both are evolved morphological traits. (The evidence supporting all these claims can be found in the papers cited below.) Women also prefer larger men and deeper voices, so there may have been an element of female choice in sexual selection, though of course the observations we make are on modern rather than ancient hominins.
  • Sexual dimorphism is also seen in our ancestors like Australopithecus and H. erectus, implying that it’s been acting on our lineage a long time. But there’s also some evidence, cited by Plavcan, that the degree of sexual dimorphism has waxed and waned as females got either bigger or smaller over time, implying that there may have been some separate natural selection in females that could increase or decrease sexual dimorphism (but never effaced it).
  • Finally, Buss’s article and others not cited outline the psychological and behavioral differences between males and females that make sense under sexual selection. These not only include the greater promiscuity of males than females, but also the greater sexual jealousy of males toward women than vice versa (our male ancestors weren’t always sure who the father of their mate’s children was, while women were far more certain). There is also a big difference between males and females in their attitudes towards casual sexual experiences (guess in which direction), and in how exacting their standards are for a short-term mate (guess again). Men have lower psychological thresholds for risk-taking. And so on. As Buss wrote, “Large sex differences appear reliably for precisely the aspects of sexuality and mating predicted by evolutionary theories of sexual strategies.”

I’ve adduced about a dozen pieces of evidence supporting the sexual selection explanation for human morphological and behavioral dimorphism—none of which can be explained by Dunsworth’s hypothesis. (And that hypothesis was dead in the water anyway, contradicted by the known data.) Since all hypotheses must, at bottom, be supported by the weight of accumulated scientific evidence, it is clear that sexual selection, and male-male contest competition in particular, is a compelling explanation for human sexual dimorphism. In contrast, Dunsworth’s hypothesis isn’t in the least compelling. That doesn’t mean we shouldn’t keep evaluating the evidence or suggesting new hypotheses, but simply that these should be supported by data rather than ideological preference.

I urge readers to look at the papers below, and use the data (and that from other papers) to evaluate theories about human behavioral and sexual dimorphism. I don’t propose to engage in a dialogue with Dr. Dunsworth about this, but I would like to know how her theory can explain the dozen-odd observations given above.

Dunsworth must have emitted something like twenty tweets about her piece, impugning me; and she even issued this over-the-top pronouncement:

Well, there’s fighting material above, but I’ve had my say. Still, I can’t believe that simply my writing a post on human sexual dimorphism and its implications would drive anybody away from studying human evolution. After all, the give-and-take of hypotheses, critical thinking, and data are the very meat of science, and if you disagree with somebody, you don’t simply walk away from a field. I sure as hell am not leaving evolutionary biology because Dunsworth and New York Magazine took out after me!


UPDATE: Things are getting worse: Peter Boghossian is arguing with Dunsworth on Twitter (I’m not involved, as I avoid Twitter Wars), but now we’re getting lumped with some rather unsavory types (except for the “evolutionists”):

h/t: Steve, David


Buss, D. M. 1995. Psychological sex differences. Amer. Psychologist 50:164-168.

Hill, A. K., D. H. Bailey, and D. A. Puts. 2017. Gorillas in our midst? Human sexual dimorphism and contest competition in men. pp. 235-249 in: On Human Nature: Biology, Psychology, Ethics, Politics, and Religion. in M. Tibayrencand F. J. Ayala (eds.) .On Human Nature, M.  Tibayrenc and F. J. Ayala, eds. Academic Press.

Puts, D. A. 2010. Beauty and the beast: mechanisms of sexual selection in humans. Evolution and Human Behavior 31:157-175.

Plavcan, J. M. 2012. Sexual size dimorphism, canine dimorphism, and male-male competition in primates. Where do humans fit in? Human Nature 23:45-67.


  1. rickflick
    Posted December 21, 2016 at 11:25 am | Permalink

    Very interesting.

    • Kiwi Dave
      Posted December 21, 2016 at 2:13 pm | Permalink

      Yes indeed! For non-scientists such as me, this is not only fascinating, but easily digestible when presented clearly in bite-sized summary form.

  2. Posted December 21, 2016 at 11:30 am | Permalink

    Proof, if proof were needed, that academic achievement and fuzzy thinking are not mutually exclusive. There’s a world of difference between scepticism and denialism, the latter of which is what Dunsworth is in fact advocating, when she refers to “thoughtful people”.

    • bric
      Posted December 22, 2016 at 3:14 am | Permalink

      And kind, don’t forget you need to be kind!. Oh by the way you are probably a nazi, have a nice day.

  3. M&S
    Posted December 21, 2016 at 11:34 am | Permalink

    Here’s a recent review on “evolutionary perspectives on on human height variation”

    Looks like a useful addition to the debate.

  4. Posted December 21, 2016 at 11:37 am | Permalink

    Stay AND FIGHT? Quite clearly ideology is her main driver. How about stay to study and research?

    • Posted December 22, 2016 at 12:44 am | Permalink

      + 1. But she doesn’t look like a person who can contribute much to research.

    • Riverman
      Posted December 22, 2016 at 1:51 am | Permalink

      I don’t remember where I’ve read that science frightens both right wing and left wing people. But facts are facts even though they threaten your ideology.
      Few months ago I’ve watched a talk about dimorphism in humans beings (form a university of Spain). First, he talked about birds, where it’s well known that there’s a strong correlation between low dimorphism and fidelity. He talked about a kind of bird that broked that correlation, because they are monogamous (same couple all their life), but they present a slight dimorphism. They studied that bird with more attention and they found out that the male cheated his partner, so indeed there are competition among males, as the theory predicted.

  5. Posted December 21, 2016 at 11:38 am | Permalink

    If you don’t like what the data tell you, the data must be wrong. She would’ve got along great with Lysenko.

    • jaxkayaker
      Posted December 21, 2016 at 7:08 pm | Permalink

      Well said, pacopicopiedra.

      Great post, Jerry. Very interesting. I see parallels such that:


      I, for one, appreciate your efforts to explain and explore ideas and the evidence, and not to personally attack those with whom you disagree.

  6. Peter Nonacs
    Posted December 21, 2016 at 11:39 am | Permalink

    Of course sexual selection is a bidirectional process which can predict both a gain or loss of sexual dimorphism. I believe there is some suggestive fossil evidence that our ancestral species were more dimorphic than us. Is it not possible then that the long term arrow of sexual selection on humans is towards a reduction in differences? This would further suggest that things like beards and larger body sizes in males are not advantages but instead slightly disadvantageous traits yet to be weeded out by selection. If perhaps humans had continued to live in small kin groups that hunted and gathered for say another 5000 generations, perhaps our species would have become like gibbons, with very little sexual dimorphism.

    • Posted December 21, 2016 at 12:06 pm | Permalink

      Yes, that’s possible, especially now that we’re more monogamous than we used to be. But still the operational sex ratio in humans is male-biased, so there’s still scope for sexual selection, though it may be weaker than before. And of course just as we retain the substantial size and musculature differences, and beards, so we could retain the behavioral differences.

    • Mark Sturtevant
      Posted December 21, 2016 at 4:49 pm | Permalink

      I know about this idea. It is largely inspired by the discovery of near-human levels of moderate sexual dimorphism in Ardipithecus, an early species of bipedal primate. The thinking is that their reduced dimorphism is the result of less male-male competition, replaced by pair-bonding and cooperative child rearing.

    • W.Benson
      Posted December 21, 2016 at 7:07 pm | Permalink

      There is, I believe, no arrow of natural and sexual selection. Just as there is no way to predict which way society will turn, there is no way to predict the direction evolution will be pushed. If civilization and tecnhology (science) collapses when the oil runs out, all bets are off.

  7. mikeyc
    Posted December 21, 2016 at 11:42 am | Permalink

    I’ve only one comment.

    I am astonished that Dr. Dunsworth would be so uncivil in suggesting anything about this discussion comes from someone unthoughtful and unkind. I have read and re-read Dr Coyne’s writing on this and I am utterly confused as to how Dr. Dunsworth could be so offended by anything he wrote.

    It is beyond reason.

    • Kevin
      Posted December 21, 2016 at 12:21 pm | Permalink

      She seems to have a contrarian agenda or motivations that I cannot pin down.

      • Craw
        Posted December 21, 2016 at 1:45 pm | Permalink

        You can’t pin them down? But this sort of thing is easy to explain: she will “fight” any scientific claim that disrupts her politics. This is precisely why fundamentalists object to evolution too. Very common amongst the humanities as well as the religious.

      • ToddP
        Posted December 21, 2016 at 2:13 pm | Permalink

        I tend to think it’s an unfortunate byproduct of the “with us or against us” mentality currently sweeping the landscape. Polite disagreement is damn near extinct, or at least has gone into hiding for a spell.

        To admit your opponent has any decent points at all is becoming the ultimate sin.

  8. Bhagwan
    Posted December 21, 2016 at 11:54 am | Permalink

    Excellent breakdown.
    All this is surprising, given that almost everything stated here is clear and evidence-based to someone with knowledge of evo biology.

    Its high time we declared there are two major ideological enemies of evolutionary biology, and Right-wing/creationism is now less dangerous than the Leftist/feminist one.

    The ways they will get their Leftist ideologies past science is by
    1. pushing postmodernist poisons – truth does not exist, science is white male whatever, facts are oppressive.
    2. calling scientists who are looking at evidence, data and facts from the point of view of truth and intellectual honesty as racist, sexist, bigoted etc to silence them.
    3. insist any criticism of THEIR theories is hate, harassment and, ironically, “ideology”.

    I’m surprised they’re even “trying” to do science. Lets see how far this one goes before resorting to the above.

    • Posted December 21, 2016 at 12:17 pm | Permalink

      Hasn’t she already resorted to the above by making the statement “but maybe I need to stay and fight”
      What is there to fight about?

      • Posted December 21, 2016 at 12:41 pm | Permalink

        There’s nothing wrong with staying and fighting with evidence. Many scientific theories were/are highly contested and subject to lots of fighting. Ultimately, the fight ends when the evidence makes clear the winner. But if she wants to prove Jerry (and everyone else) wrong, she needs to provide some evidence.

    • Zado
      Posted December 21, 2016 at 12:53 pm | Permalink

      I’m surprised they’re even “trying” to do science.

      Many (most?) anthropologists no longer are. Out of all the social sciences, anthropology has gone farthest down the leftist/activist rabbit hole. What’s more, it shows no signs of coming back up. I took an anthropology course at CU-Boulder a couple years ago, and the professor was still trying to paint Napoleon Chagnon as a racist who colluded in infecting Amazonians with small pox as part of an epidemiological experiment. I say “still” because those accusations have long been discredited. But, as we all know, ideologues disregard facts and blithely carry on.

      • Zado
        Posted December 21, 2016 at 12:55 pm | Permalink

        Is that link broken?

      • Zado
        Posted December 21, 2016 at 12:57 pm | Permalink

        No, apparently my linking is.

      • GBJames
        Posted December 21, 2016 at 12:57 pm | Permalink

        I think that depends greatly on which sub-dicipline you’re talking about. Bio-anthropology and archaeology haven’t wandered so far into lala land. I have been hearing rumors for years about the schism morphing into re-organization of departments.

        • Zado
          Posted December 21, 2016 at 1:04 pm | Permalink

          That’s true. My professor was an ethnologist, which seems to be the field most given over to activism.

          I suspect the Noble Savage myth is still quite pervasive in others though.

          • nickswearsky
            Posted December 21, 2016 at 1:18 pm | Permalink

            Now, I’m an anthropologist from a four-field school, and can say that there is still a lot of quality cultural anthropology being done out there. No more activist ethnologists than there are activist evolutionary biologists, if you ask me.

            • Zado
              Posted December 21, 2016 at 11:30 pm | Permalink

              I’ll admit: I’m probably over-generalizing and over-extrapolating about anthropology because of my experience with that one professor. The dude just rubbed me the wrong way.

              In addition to Napoleon Chagnon, he also trashed Jared Diamond and his seminal book Guns, Germs, and Steel. He brought it up in the curriculum for the sole purpose of casting aspersions upon it, one of which being that it’s author was trained as an ornithologist (because someone interested in birds couldn’t possibly be trusted to write something significant about human history).* After addressing him after class and after sampling a few anthropological forums online, I came to the conclusion that a significant number of anthropologists were irony-deficient ideologues. They opposed a book that presented the closest thing to a scientific proof of the stupidity of racism while accusing it of “geographic determinism.” Really.

              So, I have no doubt that the vast majority of anthropologists do good work in the field. I just can’t help but wonder where their heads are at when it comes to the broader picture of human evolution and history.

              *That was an allusion to Darwin, for anyone who didn’t catch it.

              • Carl
                Posted December 21, 2016 at 11:56 pm | Permalink

                I think your generalization turns out to be accurate. Anthropology is the native home for the Noble Savage myth and cultural relativism. Anthropologists are ingenious at explaining the most gruesome and bizarre cultural practices as adaptive and serving some purpose. Sick Societies, Challenging the Myth of Primitive Harmony by Robert B. Edgerton provides numerous examples showing this is not the case.

              • Posted December 22, 2016 at 12:50 am | Permalink

                To be fair, Diamond deserves some trashing. He is careless to facts and twists them to fit his ideology. I have mentioned this with his claims about pathogens, where I have some background, but I suspect the same is true about all fields covered by him. So you can learn much from Diamond, but the process is inefficient, because you have to double-check every single damn fact reported by him.

            • GBJames
              Posted December 22, 2016 at 7:06 am | Permalink

              Perhaps you are at a rare school, nick?

              I’ve known many anthropologists in my time. My dad was one. My wife and I met in graduate school (a four-field school) studying anthropology and while we eventually left the field we have many friends in the field. Our training was back in the ’70s before the pomo wave hit big time, but even then the cultural/linguistic half was way more activist than archaeologist/physical types.

              And of course, a few years back the shit hit the fan when AAA moved to remove science as the central foundation of the discipline.

              So, I think Zado hits the target, even though the conclusion is based on a small sample.

        • Jonathan Dore
          Posted December 21, 2016 at 1:15 pm | Permalink

          Yes indeed. A friend of mine studied anthropology at Cambridge, where the department is of “Anthropology and Archaeology”, and consequently their degree has that title, even though everyone holding it has only studied one of those disciplines. She said the anthropologists were a lot happier about that than the archaeologists were (i.e. the anthropolgists felt the mention of archaeology made the degree more credible; the archaeologists felt anthropology diluted it).

      • Bhagwan
        Posted December 21, 2016 at 3:13 pm | Permalink

        yep, Holly is herself one of the activist anthropologists (and a card-carrying feminist).

        we should criticize the perversion and abuse of science by left-wing activists like we (actually) do the same for right-wing activists..

        • Posted December 22, 2016 at 12:53 am | Permalink

          I think left-wing activists in science are more dangerous than right-wing ones because the latter are rarely professional scientists to begin with, and even if they are, they tend to leave their original institutions and settle at Discovery and similar ones. Left-wing activists, on the contrary, may take over universities and research centers from within.

        • Torbjörn Larsson
          Posted December 22, 2016 at 7:17 am | Permalink

          I suspected that even before I went down the anthropological rabbit hole of apparent silo compartmentalization [“four field approach”; ]. The reason is that I found out she blogs on “The Mermaid’s Tale”, which is a blog I noticed, and slowly backed away from, a few years ago.

      • nicky
        Posted December 21, 2016 at 10:12 pm | Permalink

        In the context of sexual selection I think that Laura Betzig’s “Despotism and Differential Reproduction, a Darwinian View of History” remains one of the strongest arguments where humans are concerned.
        She is an anthropologist, albeit not of the regressive kind.

    • Marc Aresteanu
      Posted December 23, 2016 at 9:45 am | Permalink

      I find it baffling how so many “intellectuals” want to keep maintaining the belief that feminism isn’t an enemy of reason.

      And before the Motte&Bailey occurs, I’m talking about actual feminism… not the dictionary definition of feminism.

      I hear people talk about the regressive Left, but then defend modern western feminism. How long we going to keep bullshitting about this? Do people know what Gender Studies teaches? It’s not a secret. It’s all there for us to see.

  9. Posted December 21, 2016 at 11:57 am | Permalink

    Great post. Keep it up, PCC. Can’t get enough.

  10. nicky
    Posted December 21, 2016 at 12:00 pm | Permalink

    Most (didn’t say all) of the length difference between human males and females is due to the later growth spurt of puberty in males. This is typically a ‘proximal’ explanation, since it does not explain why. Sexual selection does, an ‘ultimate’ ex[planation. Note that for a male, later start of reproduction can ‘easily’ be made up for under sexual selection.
    If metabolism and energy use were the main restriction on reproduction, one would expect females to grow bigger than males. As they do in many birds, fish, reptiles, amphibians, not to mention arthropods.

    I must say I’m stunned by those 11.7 and 8.6 ratios. Quite a bit higher than I intuitively assumed.

    • loren russell
      Posted December 21, 2016 at 5:39 pm | Permalink

      Those ratios are probably similar to those seen on some “dating sites” like the one exposed a couple of years ago where supposedly upscale women were in fact bots.

      • aljones909
        Posted December 22, 2016 at 4:51 pm | Permalink

        There have been some astonishing reports on Ashley Madison. e.g. “Ashley Madison hack: Just three in every 10,000 female accounts on infidelity website are real”.
        This boils down to 12,000 real accounts held by females in a 37 million account database.

  11. BlackGriffin
    Posted December 21, 2016 at 12:01 pm | Permalink

    Here’s another peer reviewed paper relevant to this discussion:
    “Darwinian sex roles confirmed across the animal kingdom”
    by Janicke et al (2016) in Science Advances (open access) under DOI: 10.1126/sciadv.1500983

  12. Posted December 21, 2016 at 12:02 pm | Permalink

    Hey Jerry, in an article published just the other day in Quillette, two social scientists expose and chastise the kind of reasoning (or should say lack thereof) by Dunsworth and like-minded people, who scream “sexism” to everything and everyone. I see a timely complementarity between their piece and yours. Some refreshing common sense.

  13. VRandom
    Posted December 21, 2016 at 12:20 pm | Permalink

    Very interesting read, however there are a few points that I cannot wrap my head around. Also, since I’m trying to make up my mind about this issue, I’ve thought about some counter points to what has been presented here.

    1) The behavioral operational sex ratio: the ratio of sexually active males to fertilizable females at a given time. This is about 11.7 in humans!

    The physiological operational sex ratio, the same ratio but for all individuals capable of reproducing (rather than those actually engaged in mate-hunting). This is about 8.6 in humans

    Okay, these are amazing facts and very surprisingly, almost unbelievable! And I’m not sure I quite fully understand it. So I have a few questions. Is this high ratio because old men are counted among ‘men capable of reproducing’ while women past menopause or pregnant women are not? If so, wouldn’t this be highly sensitive to life expectancy, and in particular to long life expectancy of women? So if the life expectancy was much lower in the past, wouldnt this ratio be closer to one?

    But I agree that nonetheless, the ratio will be far from one.

    2) In humans, as in many other species in which males compete for females, the sex ratio at birth favors males. They then die off at a higher rate due to higher risk-taking and exploratory behavior, and also senesce faster, which is why among older humans there are so many more females than males. (Check out any Gray Line tourbus.) This is predicted by sexual selction theory.

    Doesn’t the ecological reason also apply here? If males are the hunters, then it is expected that they live a more dangerous life and die sooner.

    3) In other sexually dimorphic primates, including chimpanzees and gorillas, direct contests between males can be observed, and probably existed in our ancestors since paleoanthropological data show that many more males were killed by violence than females, possibly reflecting inter-group battles, which in modern hunter-gatherer societies are often over females. Many societies also show “bride theft”, capture of females by bands of males—common in Amazonian hunter-gatherer societies.

    I think there are a lot of valid reasons to be a bit wary of comparing humans to gorillas and chimpanzees. Isn’t it true that bonobos are very different from chimpanzees in their social structure even though they are also very close to us? So wouldn’t it make sense to seriously consider the possibility that our ancestors could also have a very different social structure compared to both bonobos and chimpanzees?
    Also, how do we know males were killed in ‘inter-group battles’ and not fighting some other tribe, say in competition for food and other resources? Furthermore, the Amazonian environment is vastly different to the African savannah where we evolved so perhaps that comparison could also be misleading, specially, considering that the environment can have a major influence in our social structure.

    4)Male humans have more robust skulls than do females, including mandibles and brow ridges. This may reflect evolution to withstand blows to the head. (Males also have a higher tolerance for pain.) … Men are not only taller and heavier than women, but are stronger, particularly in the upper body …

    Again, aren’t these also consistent with the ‘males as hunters’ point of view?

    • Carl
      Posted December 21, 2016 at 12:32 pm | Permalink

      A lot of good observations and questions here. Dunsworth would have done well to consult you.

      What do you make of the “males as hunters” idea, when you consider lions, where females are the primary (not exclusive) hunters, but the sexual dimorphism is great.

    • VRandom
      Posted December 21, 2016 at 12:58 pm | Permalink

      Regarding lions, I’m not an expert so I can make at least three (probably uneducated) points:

      One, lions are not humans so it is possible that selection could work differently (e.g., see the next point).
      Two, the way lions hunt could favor a faster and smaller build for hunting but massive and bulky build for protection against competing lion groups. Female lions took the first role so they got smaller and faster but male lions took the second role so they got bigger and bulkier (of course this could work together with sexual selection to make male lions bigger).
      Three, we can be fairly certain that they way lions live is consistent with how they have been living for past many tens of thousands of years. So by observing lion behavior, we can be fairly confident in extrapolating that to the past. We can’t do that with the same degree of ease for humans.

      • Mark Sturtevant
        Posted December 21, 2016 at 5:04 pm | Permalink

        I agree with you on the lions. The larger male size is more for successful protection of the pride (his cubs, especially), and there are other similar examples like gorillas. There too, males are there to protect the young from infanticide from other males.

        • Carl
          Posted December 21, 2016 at 5:45 pm | Permalink

          Careful, larger size is not for …, but because … . The larger stronger male lions were able to obtain a pride, taking over, by killing or driving off, an existing top male, and therefore send their battle-proven genes (for size and strength, and a big mane) into the next generation. The big mane being analogous to the thick skull of men. On taking over a pride, cubs sired by other males are immediately killed.

          So it fighting, in both species, not hunting, that selects for size and strength. Male lions are actually excellent hunters, with remarkable burst speed.

          I’m speculating, of course.

    • Posted December 21, 2016 at 1:36 pm | Permalink

      Regarding your point #1, in societies without birth control almost all post-puberty pre-menopause females are almost always pregnant. This effect alone removes most females from the available pool of baby-makers for a male.

      • VRandom
        Posted December 21, 2016 at 2:15 pm | Permalink

        Hmm, are you sure about that, do you have a reference? Breastfeeding lowers fertility and freastfeeding mothers might not even ovulate for a while. Actually I wonder how much this effect the formula used to the get to this ratio.

        • Jonathan Wallace
          Posted December 22, 2016 at 2:30 am | Permalink

          But if lactating females are not capable of conception then they are also removed from the pool of available baby-makers. In the sense of Lou’s argument, nursing is simply an extension of pregnancy.

    • nicky
      Posted December 22, 2016 at 10:48 pm | Permalink

      Regarding point 2, we should not forget that the maternal deathrates were much higher in traditional societies than in our modern society.

  14. Kevin
    Posted December 21, 2016 at 12:24 pm | Permalink

    Isn’t it also true that taller stronger females, when mated to taller stronger males will produce offspring with advantages over shorter humans?

    If an Olympic athlete (>6’6″) mates with a (5’0″) female aren’t their offspring less likely to be as strong as if the male mates with a (6’0″) female?

    • Carl
      Posted December 21, 2016 at 12:34 pm | Permalink

      Sure, but the male will “mate” bit both.

  15. Zado
    Posted December 21, 2016 at 12:27 pm | Permalink

    As long as evolution, especially human evolution, is publicly championed like that, it’s not going to catch on among thoughtful kind people.

    Well, evolution is neither thoughtful nor kind. Sorry, but we didn’t descend from carefree individuals in a comfortable garden.

    Now, if we want more people to be thoughtful and kind (and I think we all do!), then it can only help to illuminate those features of our nature which we’ve inherited from our “lowly origin” that keep us from being so.

    Or we can just indulge in wishful thinking.

    • DrBrydon
      Posted December 21, 2016 at 1:02 pm | Permalink

      I was also struck by this comment. “It’s not going to catch on”? It’s not a movement, and what would be the point of publicly championing it, if we had to adjust the facts?

      • Kevin
        Posted December 21, 2016 at 1:47 pm | Permalink

        I also found the comment lacked perspective. Dunsworth might want to actually talk with scientists outside the life sciences. My experience strongly suggests a near unity agreement among physicists, for example, that evolution is fact. It’s not a movement.

        If there is a movement it should be one to make people less lazy and use their critical thinking skills.

      • Craw
        Posted December 21, 2016 at 1:54 pm | Permalink

        The part that strikes me is the “kind” part. Kind people will reject such a theory, so change it! Missing is any concern for truth, logic, or evidence. We are after all merely shopping for stories, we may choose as we please, they are but competing narratives, let us by all means pick the most congenial one.

        • Posted December 21, 2016 at 3:46 pm | Permalink

          I would argue that “thoughtful” is even worse and more offensive than “kind” in that statement. If anything, “thoughtful” people would want to examine the evidence and get to the truth. Is she implying that evolutionary biologists are not “thoughtful?” Or that “thoughtful” lay people would prefer feel good fairy tales to rigorous scientific analysis? Maybe she doesn’t know what “thoughtful” means.

          • BJ
            Posted December 21, 2016 at 5:37 pm | Permalink

            I think she’s implying that one isn’t being “thoughtful” unless they’re always keeping her pet issues in mind, and constructing narratives and interpreting any data that comes their way through the lens of said issue/s.

    • Jonathan Dore
      Posted December 21, 2016 at 1:19 pm | Permalink

      Yes, this was the statement that really underlined the gulf in fundamental assumptions between evolutionary studies on the one hand and the sort of working backwards from desired conclusions that cultural anthropology has sadly become. Really jaw-dropping that anyone with pretensions to academic rigour, deserving the title of professor, would be able to utter such a fatuous statement.

    • Mark Sturtevant
      Posted December 21, 2016 at 5:17 pm | Permalink

      Yes, I caught that too. Here, and in the earlier posts we have seen around this, the opponents always let slip a little dig where they basically say: ‘If these sexual differences evolved by natural selection, then that would justify continued male dominance and subjugation of women’.

    • Posted December 22, 2016 at 1:02 am | Permalink

      Well said.

  16. Posted December 21, 2016 at 12:29 pm | Permalink

    Some of Dr. Dunsworth’s statements – e.g. those last tweets – make it clear that ideology is a main motivator for her arguments. When someone is trained as a scientist, they are taught how to deduce and infer an approximation to objective reality from the data. For those not trained in the sciences, it can be far too easy to fool yourself into thinking data and facts (“or whatever”) can be legitimately spun to buttress any kind of story one wants. This is what happens when objectivity and, yes, emotional detachment are not prized in inference. Ideology naturally takes their place.

    From a purely ideological point of view – and from one that is incapable or unwilling to recognize that we are more than capable of creating societies that transcend our general biology – I certainly understand why some of the implications of sexual selection in humans could be hard to swallow. I sometimes wonder if such people would be more willing to reconcile with the facts if they were aware that sexual selection does not always imply some form of “males dominating females.” I think this is what ideological opponents to the science tend to fixate on.

    Maybe we should point them to hyenas, or phalaropes, or jacanas. Most of the points Jerry outlines here for evidence of sexual selection in humans are reflected in these animals as well, only with the sex roles reversed. There is also other evidence – like the phenomenon of infanticide – in some of these species that doesn’t have a direct human analogue.

    • Carl
      Posted December 21, 2016 at 12:39 pm | Permalink

      When someone is trained as a scientist, they are taught how to deduce and infer an approximation to objective reality from the data.

      I’ll just point out that Dr. Dunsworth or people like her are and have been training “scientists.”

  17. GBJames
    Posted December 21, 2016 at 12:35 pm | Permalink

    sub, part 2

  18. Allan
    Posted December 21, 2016 at 12:43 pm | Permalink

    Wow. A brilliant riposte. A little aside: I’m on holiday in Iceland on holiday. Typing this as my coach traverses a snowy road. “Bride thefts” were mentioned. Icelandic males are mostly Norse. The mitochondrial DNA sbows 62℅ of females had a lineage to females from Britain and Ireland.

    • GBJames
      Posted December 21, 2016 at 12:54 pm | Permalink

      Given we’re talking mitochondrial DNA, that would also mean that 62% of males have lineage to females from Britain and Ireland!

      • Carl
        Posted December 21, 2016 at 1:21 pm | Permalink

        That seems pretty plausible. Norse people had a large presence in the Northern British Isles and started from their settlements there (Orkney and Shetland Islands) to get to Iceland. See Saxons, Vikings, and Celts, The Genetic Roots of Britain and Ireland by Brian Sykes for details.

      • Carl
        Posted December 21, 2016 at 1:33 pm | Permalink

        I assume Allan means that the Y-chromosomes present in Iceland today descended from those originally in Viking lands.

        • GBJames
          Posted December 21, 2016 at 2:41 pm | Permalink

          I’m sure that’s the case.

          It’s just that everyone carries maternal mDNA, so the only way you would have a smaller number for men in Norway than women would be due to differential in-migration of males in recent times from Norway.

          • loren russell
            Posted December 21, 2016 at 6:50 pm | Permalink

            GBJ: Are you just missing the point, or am I? This says that the maternal ancestry is predominantly from the British Isles [yes, all the modern Icelandic mitochondria agree]. And that the paternal ancestry was primarily Norse, not British. You get the latter by looking at Y chromosomes. The most likely explanation was that many Norse men acquired British/Irish wives and not so much the other way around.

            Are we agreed?

            • Sigmund
              Posted December 22, 2016 at 3:07 am | Permalink

              Isn’t the standard explanation that the current distribution of mitochondrial DNA is due to the founder effect? The initial stock of men in Iceland were from Scandinavia while the initial stock of women included a majority from Ireland/Scotland – possibly slaves acquired during Viking raids on the northern British Isles. As the Icelandic colony grew there was little influx of additional women from Scandinavia so the Irish/Scottish mitochonria predominated.

              • Torbjörn Larsson
                Posted December 22, 2016 at 7:45 am | Permalink

                I don’t think the proportion of female thralls could have been large, if Vikings had already settled on the British Isles. Marriages would have taken place between Norse men and British women, explaining some of the genetic influx.

                Thralls would mainly be poor families that associated (most were likely forced to associate) – poor people were badly treated – and that explains some more. According to archaeology and literature träldom – and having frillor (female partners) from among trälar – was limited throughout the Viking period. [ ]

              • aljones909
                Posted December 22, 2016 at 4:33 pm | Permalink

                Torbjörn A study (link below) suggests that most white Britons have a (mostly) ancient lineage – pre-dating the Roman invasion. The Vikings left very little of their DNA behind. The anglo-saxons were the only significant contributors. The figure given is “between 10% and 40%”. So around 25% anglo-saxon seems a reasonable ball park figure.

                See New Scientist:

                “Ancient invaders transformed Britain, but not its DNA”


            • GBJames
              Posted December 22, 2016 at 7:21 am | Permalink

              We agree on that, loren.

              What I’m trying to point out is that everyone receives both maternal and paternal DNA from parents and that mDNA from mothers is shared equally with daughters and sons. So one should not expect a number much different from 62% among males in Iceland. Icelandic guys will be pretty much exactly like their sisters in terms of “maternal ancestry”.

              • aljones909
                Posted December 22, 2016 at 4:23 pm | Permalink

                GBJames. Yes, it’s pretty much 50% of our DNA from father and 50% from mother. The mitochondrial DNA allows the line of matrilineal descent to be established. In the case of Iceland a population that has been isolated for many centuries) it appears to show that that 62% of the female founding population were from Scotland and Ireland. A similar analysis of patrlineal descent (I assume analysis of the Y chromosome)shows that most of the male founding population were scandinavian.

              • Carl
                Posted December 22, 2016 at 4:37 pm | Permalink

                The Sykes book I mentioned earlier gives a somewhat different makeup for Icelandic genetics:

                We discovered that roughly two thirds of Icelandic Y-chromosomes were Scandinavian, while the remaining third were from Ireland and Scotland. However, the origin of maternal DNA was reversed, with only a third from Norway and two thirds from Ireland and Scotland. This confirmed the stories that, while most of the men had settled in Iceland from Norway, they relied heavily on women imported from Ireland and Scotland. It doesn’t necessarily mean they were taken there against their will, as the results could not distinguish between settlers who had arrived straight from Norway and the male descendants of Vikings who had spent a generation or two in Scotland. Even so, it is hard to account for the Gaelic origins of a third of Icelandic Y-chromosomes without contemplating that these men were taken to Iceland as slaves.

                Sykes, Bryan. Saxons, Vikings, and Celts: The Genetic Roots of Britain and Ireland (Kindle Locations 2807-2813). W. W. Norton & Company. Kindle Edition.

  19. Craw
    Posted December 21, 2016 at 1:42 pm | Permalink

    Excellent piece.

    Her remark about driving her away shows her motivation is ideological not truth-seeking.

  20. Posted December 21, 2016 at 2:14 pm | Permalink

    Another piece of evidence would be enlarged female breasts. In humans the breasts are mostly fatty tissue rather than milk-producing tissue (as can be seen by comparing to the much smaller size in cats and dogs), and that must surely indicate sexual selection.

    • Posted December 21, 2016 at 3:58 pm | Permalink

      Good point. And since Dunsworth’s main point of contention appears to be “don’t just talk about men evolving; women evolve, too” (as if anyone disagrees with that), she should be very happy to note that women evolving larger breasts, while men evolved larger bones and muscles, fits nicely with current theories of sexual selection causing morphological differences between the sexes. I’m actually very curious to see how this fits with her ideology. Will she reject it because women are strong and keep your eyes up here, mister! Or will she accept it and declare victory. Or something else?

      • rickflick
        Posted December 21, 2016 at 5:23 pm | Permalink

        Lake Wobegon. Where all the women are strong, the men are good looking and the children are above average. 😎

    • Posted December 22, 2016 at 1:20 am | Permalink

      This is mentioned in many sources, but I doubt it. My anecdotal evidence is that the smaller the breasts, the higher the chance that lactation will be insufficient. This is confirmed even by some in the lactation industry:

      There may be developmental correlation between fatty and glandular tissue in breasts. The issue is politically charged, because the current dogma is that every woman who really wishes can breastfeed her baby.

  21. Luke Vogel
    Posted December 21, 2016 at 2:58 pm | Permalink

    So well done. Truly, a fantastic and enlightening read. Thanks.

  22. drosera
    Posted December 21, 2016 at 3:08 pm | Permalink

    “As long as evolution, especially human evolution, is publicly championed like that, it’s not going to catch on among thoughtful kind people.”

    That’s an extraordinarily silly statement. It’s like saying, “As long as physicists tell us that gravity makes it dangerous to fall from a roof, the theory of gravitation is not going to catch on among thoughtful, kind people.”

    In fact, it is worse than silly: it’s blinkered, anti-scientific, and fallacious.

    • BJ
      Posted December 21, 2016 at 5:40 pm | Permalink

      Just as important is that when you lie to people about something, they’re less likely to believe in that something when they discover your lies. One of the many, many risks of pushing narratives you want over the truth is the discovery that you were lying all along, and then people’s refusal to believe anything you had to say in the first place. It’s like teaching kids about drugs using falsehoods and exaggerations instead of the truth.

  23. loren russell
    Posted December 21, 2016 at 3:08 pm | Permalink

    Can anyone explain why Dunsworth thinks that “girls need to stay small so they can get pregnant as soon and often as possible; men can do whatever, it’s not important” is an empowering story, while “men compete, often by fighting, women choose, sometimes wisely..” is just patriarchic?

    • Alpha Neil
      Posted December 21, 2016 at 8:23 pm | Permalink

      My thoughts as well. It’s odd that she laughs off female choice. Perhaps it’s because it implies that at least some of the asshole behaviors of men result from female preferences. If true, it would erode a bit of her precious victimhood.

      • Posted December 22, 2016 at 1:23 am | Permalink

        I admit I am happy that I didn’t end up reproducing with some of the guys I preferred when I was younger. They were charming, interesting, intelligent, but, as we say, not to be in your house.

        • Jonathan Wallace
          Posted December 22, 2016 at 2:41 am | Permalink

          With age comes wisdom!

        • Alpha Neil
          Posted December 22, 2016 at 5:00 am | Permalink

          It may just be schadenfreude, but it always seemed that the biggest jerk at the party never went home alone.

          • Torbjörn Larsson
            Posted December 22, 2016 at 7:49 am | Permalink

            “I am not the greatest gift to women there is (ahem), but I have a nice package!”

          • Posted December 22, 2016 at 2:19 pm | Permalink

            Maybe being jerk is display behavior.

  24. Pluto Animus
    Posted December 21, 2016 at 3:44 pm | Permalink

    Kudos to Coyne for deciphering that woman’s wretched writing. It is positively unreadable.

  25. Mark Sturtevant
    Posted December 21, 2016 at 4:12 pm | Permalink

    Too use a baseball phrase: That one is hit out of the park!

  26. nickswearsky
    Posted December 21, 2016 at 4:17 pm | Permalink

    I think Dunsworth is getting a bit of a bad rap, here. I read her writing, and I do think it is important to understand that selection pressures act on both males and females. Both are maximizing fitness and the strategies to do that are different given the realities of mammalian reproduction. I do think competition between males for mating access drives selection for larger body size via physical combat (or intimidation). That, however, may not be solely responsible for sexual dimorphism. Females are subject to selection pressures having to carry fetuses and care for infants. Primatology has certainly had a history steeped in patriarchy (recall Washburn or Devore). Leakey recognized that and sought women to study apes. I alway teach that males and females face selection pressures and they are not always the same. I don’t see why this has to be a fight.

    • GBJames
      Posted December 21, 2016 at 4:21 pm | Permalink

      If that were the situation there would be little dispute.

      Reread the original Dunsworth post.

      • Posted December 21, 2016 at 7:09 pm | Permalink

        I reread the Dunsworth post and then noticed that her blog The Mermaid’s Tale is also the title of a book. She doesn’t appear to be an author of the book, but the two authors do contribute to the blog. The book sounds…troubling. But it explains a lot. From one review: “They challenge the emphasis on natural selection as the primary evolutionary force…” Another review mentions “the theory’s natural implication that competitive capitalism was a natural order.” You can see where this is going, but have a look for yourself:

        • Posted December 22, 2016 at 1:26 am | Permalink

          This sounds very much like some of the writings of Lynn Margulis after her productive period was over, and before she promoted the paper about the origin of butterflies from onychophorans.

      • nickswearsky
        Posted December 22, 2016 at 8:13 am | Permalink

        She does go a bit over the top. I’m seeing she is getting a fair amount of flak on Twitter, which is perhaps a bit harsh.

        • drosera
          Posted December 22, 2016 at 1:40 pm | Permalink

          As an anti-science ideologue she deserves every amount of flak she gets.

  27. Mark Sturtevant
    Posted December 21, 2016 at 4:43 pm | Permalink

    I would be interested in learning in what way was the Richard Alexander study on polygyny and sexual dimorphism not reproduced. If the 2nd study involved another look at the same populations, then fine, it was not reproduced. But if the 2nd study involved different groups from the first, then the discrepancy could be because of differences in historical levels of competition. For example, a modern, highly polygynous society with intense male-male competition could have had historically less competition.

  28. Col
    Posted December 21, 2016 at 5:11 pm | Permalink

    “Now we don’t know about body sizes and ages of puberty in our ancestors, which is the really important information, and I doubt we’ll have that given that it’s virtually impossible to ascertain the age of puberty in fossils.”

    We know a bit about archaic human age at puberty from tooth growth patterns which seem to suggest they hit puberty earlier than we do. Haven’t read this paper in a longtime and so I’m not sure if they looked at body sizes.

    Dental evidence for ontogenetic differences between modern humans and Neanderthals. (full text free)

    • loren russell
      Posted December 21, 2016 at 8:27 pm | Permalink

      Neanderthals are not especially archaic, and not necessarily closer to earlier Homo than H. sapiens in any particular trait. Since there are no decent ontogenetic series in any earlier Homo, the idea that modern humans reach puberty later is possible but hardly proved.

      Of course, the age of puberty comes down rapidly in well-fed populations.

  29. Bill
    Posted December 21, 2016 at 8:12 pm | Permalink

    At puberty, it’s not just that girl’s bi-iliac measures grow wider, but moreover it’s that boy’s biacromial measures get wider — i.e. boys transform into a body shape that is more fit for fighting/throwing. It’s also long known that androgens potentiate insulin in muscle while estrogens potentiate insulin in adipose tissue. Exogenous testosterone will grow as much muscle in an inactive male as one who works out in a gym without exogenous testosterone. This is all basic anatomy and physiology taught in the freshman/sophomore years.

  30. nicky
    Posted December 21, 2016 at 10:56 pm | Permalink

    As asked on the earlier thread. How come the sexual dimorphism in humans was maintained throug struggle between males, while at the same time we are so much weaker (whether twice, thrice or more is irrelevant to the question) than our closest cousins.
    [Apparently it is the lack of expression of a specific gene that causes hairlessness and weaker musclefibre]
    Has anybody any idea?

    • Carl
      Posted December 21, 2016 at 11:02 pm | Permalink

      Because we aren’t competing with our close relatives for mating opportunities, only with our own species.

      • nicky
        Posted December 22, 2016 at 1:38 am | Permalink

        I find that answer somewhat unsatisfactory. During ‘transitions’, the ‘hairy strong ones’ would still have a definite advantage in the male-male struggle for mates, the struggle that maintained the dimorphism.

        • Physicscat
          Posted December 22, 2016 at 8:12 am | Permalink

          > During ‘transitions’, the ‘hairy strong ones’ would still have a definite advantage in the male-male struggle for mates, the struggle that maintained the dimorphism.

          Once you separate the populations (e.g. geographically) then would no longer be competing for the same mates and so the opportunity for the males of each group to diverge in strength arises.

          • FiveGreenLeafs
            Posted December 22, 2016 at 8:48 am | Permalink

            Indeed. I also think it is important to keep in mind, that there can be several evolutionary “forces” acting on a specific population at the same time.

            Being as big as a gorilla, might have been positive in a fight for mates, but, if food is scare, and you have to travel a lot to find it, being as big as a gorilla increase the risk that you will die of starvation before you even have a chance of mating with anyone…

            The evolutionary outcome is (to my mind) often a compromise of many such forces, that can work in different directions at the same time.

            The human/chimp common ancestor who found themselves out on the Savannah with dwindling trees and food sources, experienced a very different set of challenges than the same ancestors living in the surviving rain forests further west.

        • Torbjörn Larsson
          Posted December 22, 2016 at 8:16 am | Permalink

          Good question. I don’t think the strength differences, which is nearly an order of magnitude IIRC (some five or more times), likely comes down to just one allele or gene. In most cases traits like length, mass, and possibly strength are polygenic.

          And we do differ in skeleton and muscle attachment, where typically other hominids have larger lever arms. However that evolution was mosaic. Still, could the savanna hypothesis explain it? I.e. possibly the fitness increase from living in more bushy/grassy environment would have drowned the decrease that weakening first the lower, then the upper body strength (and eventually all of it, as per your gene example) would induce. Strength may have been of little use against savanna predation, say. But being nimble, fast, having running endurance and being a better tool user (throwing sticks and stones) was possibly better. The same factors goes for food gathering too, though maintaining sexual dimorphism would imply sexually differentiated such, whether scavenging or hunting vs gathering. [What would Dunsworth say!?]

          • nicky
            Posted December 22, 2016 at 6:50 pm | Permalink

            Yes, I understood from Steve Jones (as said, he irritatingly gives no reference) that it is a single gene.
            I fail to see how relative hairlessness and loss of strength would convey any advantage in a savanna environment (I don’t say there isn’t, but what could it have been?). How does it make one more nimble, fast or makes one a better runner or tool user?

          • rickflick
            Posted December 22, 2016 at 7:09 pm | Permalink

            It’s probable that humans hunted by chasing down prey. Running until the antelope became too exhausted to continue, allowing male Homo Sapience to close in with a coup de grâce from a spear or two. Running for many hours in the hot sun requires effective cooling of the body and brain. Sweat glands are effective, but not when covered by too much hair. An overly bulked up, big armed short legged, creature is poorly equipped for sustained running. Today’s Olympic marathoners are gracile not built like Schwarzenegger.
            This method of hunting is used today by some African hunter gatherer societies.

            • nicky
              Posted December 22, 2016 at 7:35 pm | Permalink

              Yes, the Bushmen use it, combined with the fact that a chased antelope runs in a wide circle (IIRC), so they can ‘cut some corner’.
              However, no other running savanna animal (save elephants and rhino’s) are hairless, and hairy runners such as horses do sweat, hair or no hair. [And then we are not talking subcutaneous fat, did that arise with hairlesness?]

              • rickflick
                Posted December 22, 2016 at 9:54 pm | Permalink

                Good questions. At this point we may only be able to generalize. I assume the particular path humans took in terms of thermal regulation came about from the specific conditions when nakedness evolved. Same for lions, which pant to cool off, elephants flap their ears, Cheetahs have large aerated sinuses to cool the brain, hippos wallow and feed at night, horses shed in summer. All these adaptations came about from the specific architecture that preceded the need for them.
                Wasn’t it Desmond Morris who wrote The Naked Ape? As I recall, he speculated that nakedness was conducive to appreciating the fitness of a member of the opposite sex. He sold a lot of books with that idea, but I don’t know if it’s been verified in any way.

        • Pete T
          Posted December 22, 2016 at 8:33 am | Permalink

          The big, strong, hairy selection pressures should not be thought of in isolation. There are contrary selection pressures which are favouring smaller, weaker, balder traits (if an individual is wasting too many resources on growing big there are less spare for reproductive purposes, big bodies require more nutrition to support, upper body muscle bulk may be a trade-off against speed or endurance). What we end up with in a population is a distribution around a compromise.
          It should not be surprising that our more forest-dwelling cousins reached a different compromise to us more plain-dwelling apes. The male individuals who became a little bigger and stronger than the rest may well have been favoured by the females but at too much of a survival cost in terms of feeding themselves to pass these genes on. Those individuals who got the compromise right had the most grand-children.

          • nicky
            Posted December 22, 2016 at 6:40 pm | Permalink

            We are not talking about wasting resources in growing big, we are talking about losing strength and hair. And remember, males remained bigger than females in the male to male struggle.
            However, I agree that there probably was/were other selection pressure(s). The question is which one(s). Possibly something from the female side?

          • rickflick
            Posted December 22, 2016 at 10:03 pm | Permalink

            I think in general you can refer to the balancing of bodily resources as an energy budget. Every structure has an energy cost, meaning a certain caloric intake is required to grow and maintain the structure at a given size. This puts an upper bound on the size of muscles for an organism capable of finding only a given amount of calories in food. If the increased size of muscles is offset by an increase in the ability to acquire food, then the muscle growth can be adaptive, and so forth.

        • Posted December 22, 2016 at 8:37 am | Permalink

          Other selective pressures still exist – that the genus Homo lost strength and hair compared to our closest relatives doesn’t mean that sexual selection *didn’t* push for stronger, hairier males.

          You could ask why peacocks don’t have tails that are tens of meters long and have thousands of tailfeathers – the result of evolution is determined by the balance of selection pressures, not by a single one, at the same time, sexual dimorphism tends to be dominantly caused by sexual selection, but always within the boundaries set by other selective pressures.

        • darrelle
          Posted December 22, 2016 at 8:44 am | Permalink

          The implication would seem to be that whatever the selection pressures were for hairlessness and or weaker musclefibre that they were of greater magnitude than sexual selection pressures for greater physical abilities.

          Perhaps brain size increase, jaw size / strength decrease and minimum calorie budget requirements were involved.

        • FiveGreenLeafs
          Posted December 22, 2016 at 9:09 am | Permalink

          Another aspect is that our human ancestors, perhaps already for 2 million years ago, started to use tools like spears.

          And, being a “hairy strong one”, didn’t count for much (ask any mammoth), when you opponent wields such technical innovations.

          And the weak hairless ones managed to eradicate a stunning number of “hairy strong ones” on each and every continent they populated.

          The catch is, that being good at throwing spears (and avoiding being hit by one) is not facilitated if you are build and have the figure of a sumo wrestler, aka gorilla…

          • nicky
            Posted December 22, 2016 at 6:32 pm | Permalink

            Yes, but we’re talking within a group or population. How does weaker musclefibre and/or (relative) hairlessness confer more agility or prowess at spearthrowing? (While stiĺ maintaining sexual dimorphism

            • FiveGreenLeafs
              Posted December 23, 2016 at 12:08 pm | Permalink

              It was a reductio, with the aim to try and make the critical aspect more visible, but I must have failed to convey that clearly enough, or, you failed to understand…

              The same forces working between or on different species, can of course (as I see it) work equally well within species or subpopulations.

              And, many forces can be at work at the same time, sometimes in opposite directions. You must therefore think in multivariate space!

              I really don’t understand what your issues are here, and wonder if you perhaps fail to grasp or understand, on a more fundamental level, how natural and sexual selection actually (are believed to) work?

    • reasonshark
      Posted December 22, 2016 at 8:52 am | Permalink

      One answer, I think, is that sexual selection determines relative strength within a population, to the backdrop of whatever other evolutionary forces are working on, say, the species’ general musculature. For whatever reason, the daily lives of our distant ancestors did not need extreme musculature and indeed might have favoured diverting resources into other body systems (most obvious example would be increased brain size). That would trigger, over many generations, a reproductive advantage for weaker bodies but bigger brains, say, and it would be countered only slightly by the evolutionary pressure for stronger male bodies.

      Another, though I think less possible answer, is that the evolutionary pressure for sexual dimorphism was simply even more extreme in our relatives. Gorilla males, for instance, are immensely strong and always live in a harem-style group structure, while gibbons are relatively weak and form monogamous pairs. Humans might simply occupy a point somewhere between the two extremes, though I don’t know how well that hypothesis is borne out by the data.

      • FiveGreenLeafs
        Posted December 22, 2016 at 9:21 am | Permalink

        “the evolutionary pressure for sexual dimorphism was simply even more extreme in our relatives”

        I am not so certain that it was. Sexual dimorphism in upper body strength between human males and females is roughly of the same order of magnitude as physical size for gorillas.

        Gorillas fight by sheer brute force (of weight), by running against each other, human males have not (in all probability) done so for million of years.

        Throwing a spear with accuracy (for example) requires a very different set of physical attributes, like upper body strength, agility etc.

        • reasonshark
          Posted December 22, 2016 at 9:29 am | Permalink

          Good point that I can’t really argue with. Human tool-making complicates the issue, as does our ability to form alliances rather than just fight one-on-one.

          • FiveGreenLeafs
            Posted December 22, 2016 at 12:38 pm | Permalink

            I think tool making modifies and changes the parameters and attributes we need to consider, to accurately estimate the degree of male competition and sexual selection.

            And I think you put the finger on another very important aspect in that regard, the ability to form alliances.

            As far as I understand things, in chimp societies, it is not always the strongest that end up on top of the hierarchy, but (often) those that can form and sustain strong and lasting alliances.

            Which leads back to the issue of sexual dimorphism in the neurological and cognitive domain, and the observation that (for example) the connectivity in the brains of boys and girls appears to look pretty much alike up to puberty, but, seem to diverge dramatically afterwards…

      • nicky
        Posted December 22, 2016 at 7:20 pm | Permalink

        Does relative hairlessness and weaker musclefibre (we are not talking muscle mass) divert enough to assist in enough brain development to be advantageous? Especially since dimorphism was maintained. Braindevelopment has been a prolonged process, the loss of hair and strength (since only one gene/allele) probably not. I do not find it very convincing, but I may be mistaken, of course.
        Maybe females just preferred ‘naked’ males? Better exoparasite detection? All very speculative.
        Are hairy gibbons relatively weak? Small, yes, but weak? And they -as monogamists- have little dimorphism.

  31. Posted December 21, 2016 at 11:41 pm | Permalink

    Great reference, thank you Jerry for putting this together.

    I’ve read the spectre of biologism, reductionism or scientism was haunting such controveries, but I have not yet spotted it in wildlife. I’ve seen a wisp, perhaps, but no the serious spook I’ve been warned about. Most of the time, when you ask the concerned, they show you a scarecrow made of straw, dressed in a stereotypical labcoat.

    Everybody worth taking seriously knows of the complicated interplay of nature and nurture and are careful about it. Nobody says differences between the sexes are all biological. But plenty exist who claim the opposite in the humanities and activist circles, where views like “all is culture”, “Blank Slate” or “facts/sex/gender are socially constructed” are common. They are also in the mainstream now, thanks to the resurgence of Tumblr-postmodernism.

    MTV-backed Laci Green who has her own YT channel of nearly one-and-a-half million subscribers claims sex and gender are culturally constructed. Granted, such views occasional are not as radical as they sound like, and turn out to be confused and murky nonsense, or are the familiar postmodernist ambiguity of radical in one interpretation, but trivially true in another (now often called “motte-and-bailey doctrine”). Yet, this stuff works because a sizeable crowd wants to believe it and is not too keen on critisizing such ideas.

    For those interested to learn about sexual dimorphism avoid Laci Green et al, and turn to Robert Sapolsky’s Stanford lectures with plenty of additional material and data.

    He discusses reproductive strategy in one part and how humans are between pair-bonding and tournament species. He’s also not fond of biological determinism, either. He studied a fascinating case of baboon culture, where through an accident, aggressive males poisoned themselves when they fought over and ate from toxic rubbish in a reservat. The mellower individuals survived, and oddly, newly arrived aggressive males adjusted their behaviours and became mellow, too, after a short time. Cases like this show there’s not a strict biological determinism, but nature — in uncountable ways — sets limits of what is possible and a kind of prospensity, which we see as tendencies. A continuum of possible states can be “choked” through pressure, environmental or sexual and then in turn emerge stronger in the genepool (through stronger selection pressure, not Larmarckian).

    Let’s suppose only lottery winners were allowed to reproduce. Since this is purely cultural, it will leave no imprint in the genes. But if a society only allows its top runners to mate, we’ll expect that over time this cultural choke-point will emerge in the genepool, because a genetic factor can be emphazised and selected, as only good runners leave offspring. We have such choke points in culture: the top Nobel scientists, the best athletes, or just jobs that are seen as about bending over arcana formulae competing with professions that seem more fulfilling for the average Joe, but especially Jane.

    Sexual behavioral differences can be small, actually, but when only the “tails” of the distribution pick up a profession (choice) or are able to compete (selection), we should even expect (!) to see sexual differences emerge in the given population. The confusion seems to be between stereotype (women or men are such and such) with the real tail outliers, and it’s not hard to see why. When the long tail outliers occupy a profession, for example, it can easily feedback into perceptions of the entire population, and then create a feedback effect (e.g. it’s also seen as manly or unwomanly to pick up profession X).

    Such examples can illustrate the interplay of nature and nurture, which are anyway idealized (humans idealize through categorization anyway, and there’s also the Tyranny of the Discontinuous Mind).

  32. Christopher
    Posted December 21, 2016 at 11:44 pm | Permalink

    glancing at her tw*tter feed I was sad to discover a myrmecologist whose bl*g and tw*tter I used to follow was praising her intellectual bravery. It reminded me why I emptied my tw*tter of many otherwise intelligent scientists who were increasingly showing a disturbing obsession with regressivist ideologies. Quick jumps to judgment without the facts, or in spite or the facts, or in this case, replacing facts with ideology are things I expect of people in the humanities, but it always comes as a shock to the system when a scientist does so.

    Perhaps it is a good time to be reminded of that golden rule of science from Richard Feynman: “The first principle is that you must not fool yourself and you are the easiest person to fool”.

    Thanks for fighting the good fight, Prof.

  33. Dimitris Klaras
    Posted December 22, 2016 at 2:25 am | Permalink

    About “sexual selection” first and last I heard from Jared Diamond’s books especially in “The rise and fall of the third chimpanzee”. But not to explain “sexual dimorphism”. Actually I heard this term first from Jerry. I searched Diamond’s book and this term is nowhere to be found. Diamond’s uses this theory to explain the different “race characteristics” in humans. An expert found in this book:

    But I shall argue in Chapter Six, as Darwin maintained, that our visible geographic variability arose mainly through sexual selection, as a result of those matechoice procedures of ours discussed in Chapter Five.

    The title of chapter six is: “SEXUAL SELECTION, AND THE ORIGIN OF HUMAN RACES”

    I remember a story about Papua New Guinea where men find white women very ugly. And if we look at Papua New Guinea women probably we will think them as good antidote to sex offenders:

    One evening, while I was camping with some New Guinea men of the Fore tribe, the conversation turned to women and sex, and my Fore friends proceeded to explain to me their tastes: The most beautiful women are Fore women. They have gorgeous black skin, thick, dark frizzy hair, full lips, broad noses, small eyes, a nice smell, and perfectly shaped breasts and nipples. Women of other New Guinea tribes are less attractive, and white women are unspeakably hideous. Just compare your white women with our women to see why —white skin like a sick albino’s, straight hair like strings, sometimes even hair coloured yellow like dead grass or red like a poisonous snail, thin lips and narrow noses like axe blades, big eyes like a cow’s, a repulsive smell when they sweat, and breasts and nipples of the wrong shape. When you get ready to buy a wife, find a Fore if you want someone beautiful.

    • nicky
      Posted December 22, 2016 at 7:42 pm | Permalink

      Well, the Fore have a point, ne? 😊

  34. Posted December 22, 2016 at 3:50 am | Permalink

    Reblogged this on Why Darwin Matters.

  35. JJthomson
    Posted December 22, 2016 at 7:27 am | Permalink

    This has generated a rather interesting conversation over on the skeptic subreddit

  36. BJ
    Posted December 22, 2016 at 9:02 am | Permalink

    Regarding your update, you’re just seeing the same tactic people like Dunsworth have been using for years now: call anyone who disagrees a sexist, racist, bigot, and/or harasser, and most of the ideologically driven and regressive will automatically see it as a “win.” Once the right label is thrown out, there is a sizable portion of the population who will discard any disagreement as falling under that umbrella.

    This tactic has served to make many people wary of these labels in the first place when they see them. They’ve watered these words down so much that the words have become immediate signals that one must take a closer look to find the truth, as their use is so often a sign that someone is trying to dismiss something that they can’t otherwise dismiss.

    • Carl
      Posted December 22, 2016 at 11:30 am | Permalink

      This tactic has served to make many people wary of these labels in the first place when they see them. They’ve watered these words down so much that the words have become immediate signals that one must take a closer look to find the truth, as their use is so often a sign that someone is trying to dismiss something that they can’t otherwise dismiss.

      This is an excellent observation, but rather than look closer at claims flinging labels with abandon, I find myself ignoring them more and more.

      • Craw
        Posted December 22, 2016 at 2:47 pm | Permalink

        And we see the predicted inflation at work now that the currency is debased: I increasingly see “white supremacist” being used where “racist” would have been flung out a year ago.

  37. Posted December 22, 2016 at 9:14 am | Permalink

    The intersexual genetic correlation in body size between males/females is quite high. Hence, even if males were under strong directional sexual selection, and females were under stabilizing selection for fecundity, the strong genetic correlation between the sexes would “pull” female body size toward male body size (until the correlation breaks down, and males and females find new size optima…as predicted under Russ Lande’s model of sexual dimorphism)

    This is interesting to think about since it suggests that sexual selection may actually be very strong in males, but the dimorphic effects are muted due to the intersexual correlation.

    But it could also suggest that selection on female body size (e.g., stabilizing selection on viability or fecundity) could also influence male body size. However, there is a sound theoretical case for why sexual selection acting on males is among the fastest/most potent forms of selection, swamping out the effects of viability/fecundity selection on females (and other forms of selection on males); this is laid out clearly in Shuster and Wade’s book on sexual selection chapter 1. So it is unlikely that selection on female size could influence selection on male size as strongly as the converse.

    Another possibility is that stabilizing sexual selection acts on human males, favoring traits like agility/maneuverability over large size, as seen in some birds. This would mute the effects of size dimorphism.

  38. jrhs
    Posted December 22, 2016 at 11:45 am | Permalink

    Interesting. Thanks to all. I learn not only something about evolution but also how not to handle disagreements. Rationalization or self-justification may help us sleep better at night, but may not be a good thing.

  39. Posted December 23, 2016 at 1:29 am | Permalink

    Although my husband was tall, manly and strong,(played football and baseball, was a hot shot fireman for three summers as a teen, loved the outdoors all his life, etc.), I loved him most for his mental gifts, his knowledge, his curiosity, his musical abilities, his philosophical bent, his sense of humor, his lifelong pursuit of knowledge, his desire to share with all,etc. Intelligence is a most attractive quality. I was grateful to have shared life, knowledge, joy and humor with him for 56 years. He still had all those qualities when he died in January of this year. His qualities live on in our children.

    • rickflick
      Posted December 23, 2016 at 4:42 am | Permalink

      What a beautiful tribute.

    • HaggisForBrains
      Posted December 23, 2016 at 8:33 am | Permalink

      My heart goes out to you, and you reflect my way of choosing the women* I love.

      *Plural because after losing a wife that fitted your description, I’ve had the good fortune to meet another. That she is beautiful in my eyes as well is merely a bonus.

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