Sexual selection vs job specialization

Pretty much every species is subject to sexual selection: heritable characteristics that lead to more mates or better mates can be favored by natural selection. Typically, sexual selection favors different strategies in males and females. Generally, males can gain fitness with increased mating opportunities, while females gain more from high-quality mates or mates that confer resources. Since the variance in reproduction is usually greater in males than females, sexual selection is usually stronger in males, although it exists and is significant in both sexes.

Usually, though, males and females of a given species have very similar ways of making a living. A male deer and a female deer both eat grass or arugula or whatever. Sexual selection may drive them to evolve in different directions, but finding something to eat mostly drives them in the same direction.

Humans are an exception. In the long past, men hunted and women gathered. The mix varied: in Arctic regions, men produce almost all the food (while women made and repaired gear, as well as raising children). In groups like the Bushmen, women produced most of the calories, but done rightly you would count more than calories: if most of the local plants had low protein or low-quality protein (wrong amino acid mix), meat from hunting could be important out of proportion to its caloric value.

This has been going for a long time, so there must have been selection for traits that aided provisioning ability in each sex. Those job-related selective pressures probably changed with time. For example, male strength may have become less valuable when the Bushmen developed poison arrows.

I was looking for an intelligent discussion of this question – but I ran into this and couldn’t force myself to read further: ” It should not simply be assumed that the exclusion of women from hunting rests upon “natural” physiological differences. ”

God give me strength.

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75 Responses to Sexual selection vs job specialization

  1. Bobo the chimp says:

    Chimpanzee hunting of monkeys is also male-only:

  2. Frau Katze says:

    Scare quotes around “natural”. So we are considering supernatural? Can physiological differences be a social construct?

  3. Sandgroper says:

    No no, it has nothing to do with natural physiological differences – it is the white male patriarchy retaining control of the meat/ostrich egg resources in order to establish and exert their dominance. Oh wait…

  4. PhysicsEngineer says:

    I have a question about sex selection of a different kind – i.e. how much randomness there really is when determining the baby’s gender?

    It seems to me that males have a genetic predisposition towards creating more of one type of sperm, but I’m not sure whether this is only related to testoterone levels.

    There’s also dr Shettles theory, which basically claims that it’s all about timing; supposedly male-producing sperm are smaller, faster and more fragile than female producing sperm, so intercourse at the time of ovulation skews the odds in favor of boys.

    I’m not sure what to make of this theory. Other sources claim it is rubish, but then again most of those sources deny that racial and gender differences exist.

  5. st says:

    Easy to refute. Hunting was dangerous, higher numbers of fatalities than gathering. Say there were hunting females. Death during hunt = death of any offspring under age of 3 depending on the breastfeeding by the hunter. Males cannot breastfeed – can they? So female prone to hunting would be selected against in any condition or environment, arctic to desert. And they were selected against. Or…
    M-r Cochran, I got a question for you. Would you consider the rise of eusociality related to the selective pressure against hunting females? (hunting sisterhoods became infertile and the species go eusocial?)

    • MawBTS says:

      I’m not Greg, but I don’t believe eusociality exists in humans.

      It would be maladaptive if it did.

      • st says:

        I did not have humans in mind. Ants. There has been ongoing argument what kind of odd evolutionary event would have triggered eusociality in their species, as it has been firmly believed that rise of eusociality would have been a mathematical oddity with no math grounds in evolutionary theory. That’s why I asked Greg but I do not mind you answering it…

      • why maladaptive? because number of individuals in group not large as in insects?

        • MawBTS says:

          It’s a question of relatedness. Most eusocial behavior is effectively altruism – hurting yourself, to help your neighbors. When a harvester ant brings a crumb back to the nest, it’s taking food out of its own mouth to feed its brothers and sisters.

          It works for ants in a nest, because they’re all 50% related to each other. The eusociality gene remains stable. But it wouldn’t work in humans, because our relatedness to a random human is basically zero (except for our immediately family). We’d waste lots of time helping random strangers who don’t have the gene.

          • brokenyogi says:

            Given that most of human history involved small groups of 40-50 humans wandering about hunting and gathering, and that most of the people in those groups were essentially part of an extended family, eusociality would generally not be random or involve unrelated strangers. Only those within the clan, or neighboring clans that had broken off into their own groupings, that were probably also related, would benefit from eusocial behavior. So there would be limits to eusociality, and break down entirely when encountering clans of strangers. So eusocial behavior within these social limits would be selected for in most cases.

          • pollux says:

            You’re forgetting about haplodiploidy, which is hugely important in the evolution of eusociality. Sister ants are actually ¾ related.

    • Greying Wanderer says:

      “Easy to refute. Hunting was dangerous”

      yep – “eggs are expensive, sperm is cheap” works as the default explanation most of the time

      even if males/females started out exactly the same they would evolve differently just cos of that

  6. st says:

    O, wait. I start seeing an extinction event here, happening nowadays -but only in industrialised societies. Interesting. Thank you for the interesting post, M-r Cochran.

  7. MawBTS says:

    What does Greg think about the “plows vs hoes” theory? (As seen here, although Sarah Constantin didn’t invent it.)

    The claim is that some societies adopted farming (Europe, the Middle East, Asia) while some societies adopted horticulture (Oceana, sub-Saharan Africa, various primitive peoples) and that this had an affect on gender relations.

    Basically: farming is backbreaking work, which favours males, giving them a lot of social capital. You end up with a patriarchal kind of society, where the men do stuff and the women are mostly valuable for raising offspring.

    But horticulture is relatively accessible to women, and these sorts of cultures tend to be a bit more egalitarian (for example, a woman in Europe can’t run a farm on her own, but a woman in Uganda can run a garden on her own), because women aren’t dependent on men for survival.

    It’s pretty speculative and I have my doubts that “hoe cultures” are feminist wonderlands (lots of FGM and femicide in sub-Saharan Africa, for example). And it seems even hoe cultures do a lot of hunting or fishing, which, again, favours men.

    A lot of the literature seems to have been written by Margaret Mead types, fondly imagining distant lands as paradises untouched by the rapacious male id. In general, I mistrust the things cultural anthropologists write about primitive people. They view them as mirrors, with their own ideals reflected back

    • gcochran9 says:

      It’s kinda true, in places. There is a connection I haven’t seen explicated: the ‘hoe culture” has to have some factor keeping population density low, so that labor is scarcer than land. Tropical diseases like malaria might be part of that. Then again, crops like yams don’t store well, better to keep them in the ground until eating. That means it’s hard to tax people – easy with grain bins. No taxes -> no State – > high local violence. At times, VD may also help limit density, cf Africa’s ‘sterility belt’.

      • Greg,

        It is generally acknowledged that earliest agricultural villages in ancient Sumeria were horticultural (having existed long before the invention of the plow) and were also characterized by female fertility goddesses. Anthropologists think that they were also matrilineal societies and perhaps matrilocal as well, though not of course matriarchal, since there never was such a thing. (I think I read somewhere that a similar cultural complex existed in the Balkans, at least according to a famous female anthropologist whose name I forget.?). Women developed horticulture and as a result enjoyed relatively high status those early horticultural societies that depended on horticulture as their primary source of sustenance.

        Anyway, since these early horticultural societies predate the rise of large complex political states, whose growth was fueled by military conquest (including defensive strategies to prevent being conquered), it is perhaps not coincidental that the oldest word for freedom in Sumerian (which I suppose means in any language) is amargi, whose literal translation is “return to the mother.” And seeing that large-scale conquest as a political institution was not practical before the rise of settled agriculture over fairly extensive and densely settled regions, as existed first in southern Mesopotamia, this explains why Eve gets the blame in the story. Along the same lines, if human beings hadn’t been so smart as to figure out how to grow food there heads would have been smaller and women wouldn’t suffer so much during childbirth!

        I write about some of these things (see link below) in a letter I once sent to Jack Goody, in which I lay out my hypothesis that the story of Adam and Eve was originally an allegory of conquest (using allegory in the original sense as being an elliptical story about things of which it was forbidden to speak directly). It’s disguised subject was the end of the neolithic world, which was based upon horticulture and was relatively free and egalitarian, and the beginning of the “patriarchal” world of peasant servitude, which of course characterized all pre-modern civilizations prior to the industrial revolution.

        So far I don’t think I’ve convinced a single solitary individual that this hypothesis might have something to recommend it, so you are welcome to be the first: https://goo.gl/uikvFb

        • Gord Marsden says:

          I wonder if the story of Jacob and Esau is an explanation of the same. Hunter vrs farmer.

          • Gord Marsden says:

            Add to it that one is hairy like a Neanderthal and one is smooth and modern

            • Let’s assume for the sake of argument that Neanderthals were hairy. There’s no hard evidence for this that I know of, but what the heck. Say there was. Then they go extinct, maybe 40,000 years ago, back when all sorts of humans, including Neanderthals, lived as hunters and gatherers. Thirty thousand years — one thousand human generations ! — pass, but people specifically manage to remember that there were once hairy Neanderthals who hunted.

              Maybe 10,000 years ago, farming starts becoming popular in the Middle East. People think, hmmm, we’re not very hairy, and we farm now. But a thousand generations ago, some of the hunters out there were very hairy. So let’s associate being hairy with hunting.

              Maybe 5,000 years pass, say 270 generations, during which time people continue to associate smoothness with farming and hunting with hairy Neanderthals. All this is done orally, generation by generation, by word of mouth, with remarkable fidelity.

              Maybe 5,000 years ago, people start writing stuff down. Maybe some of this stuff finds its way into writing, maybe it keeps on getting passed down orally. Since we’ve had something like 1300 generations of people remembering the Neanderthals orally, it makes little difference whether we stipulate a few more thousand years of oral tradition, or a few thousand of writing.

              2,500 more years pass. Someone writes down the Jacob and Esau story, vaguely inspired by the Neanderthals of 1250 generations before. So the Bible contains traces of real history over a thousand generations old. And yet, at the same time, the biblical writers thought they were, as the genealogies have it, just about 50-60 generations from the creation, and just about 30-40 generations from people who lived hundreds of years.

              Huh. What a weird story.

              • Greying Wanderer says:

                i take your point but just out of interest google “hairy barbarians”

              • BB753 says:

                There’s also the Sumerian myth of Gilgamesh.
                Enkidu was the wild hairy one, Gilgamesh the civilized, smooth king of Uruk. The story goes that Enkidu was enticed away from the wild forrest by the temptress Shamhat. Could that be a distant memory of human/Neanderthal intercourse?

              • gcochran9 says:

                “Could that be a distant memory”

                No.

              • Well, we could try and concoct a scenario where the supposed existence of hairy Neanderthals 40,000 years ago somehow gets recorded in distorted form via stories that associate hairiness with wildness 2500-4000 years ago. That’s one option. Another option is that animals all are covered in fur, and people aren’t, and therefore that various folklore from Enkidu to Beauty and the Beast uses hairiness to represent being animalistic. An advantage to the animals-are-furry option is that we do know, for a fact, that animals are furry, and that we don’t need to come up with methods by which the knowledge of furry animals was preserved over hundreds of human lifespans.

            • Greying Wanderer says:

              “Add to it that one is hairy like a Neanderthal and one is smooth and modern”

              they don’t have to be a hairy archaic – they could be people who were slightly more archaic i.e. if they lived up mountains then any archaic cold weather adaptations might have survived more than down in the valleys – the relevant difference in DNA might be low, like 1.2% or something.

        • Sandgroper says:

          “a famous female anthropologist whose name I forget”

          I believe you are referring to Marija Gimbutas. She was pretty right about some things, to her credit, and barking mad about others.

        • Sandgroper says:

          And not to split hairs, but Gimbutas was an archaeologist, not an anthropologist.

        • MawBTS says:

          It is generally acknowledged that earliest agricultural villages in ancient Sumeria were horticultural (having existed long before the invention of the plow) and were also characterized by female fertility goddesses.

          I don’t think that means anything. Lots of plow cultures have fertility goddesses.

        • Labayu says:

          “Anthropologists think that they were also matrilineal societies and perhaps matrilocal as well, though not of course matriarchal, since there never was such a thing. (I think I read somewhere that a similar cultural complex existed in the Balkans, at least according to a famous female anthropologist whose name I forget.?).”

          The name is Ruby Rohrlich. She also wrote “Peaceable Primates and Gentle People: An Anthropological Approach to Women’s Studies”. If we set aside Rohrlich’s speculations regarding what depictions of female deities mean about Sumerian prehistory as she imagines it, and just stick to mundane evidence such as legal documents and letters between family members, it’s quite clear that Sumerian society was both patrilineal and patrilocal, at least from the point we know anything of substance about it.

          It’s been awhile though, so if you recall her forwarding any solid evidence in support of her various speculations, please remind me.

    • kn83 says:

      Its somewhat true in some (key word) ways that women are more independent in historically horticultural peoples than in hunter-gatherer and farming peoples, since they don’t need males for survival.Yes there is rape, fgm and to a lesser extant female infanticide, but it explains how black african women (relative to the males) have a higher degree of control and influence in their societies than white euporean women. You even see a similar effect when comparing black american women with their white counterparts.

  8. Keemaker says:

    exclusion of women

    I start hearing the rhythmic sound of a rotor blade whenever I read that specific combination of words.

  9. Yeyo says:

    You do see a similar kind of job specialization in a few other group living mammals though, lions being the most famous example. Of course male lions need to hunt for themselves before establishing a pride but they haven’t evolved the same group hunting skills as lionesses. Might help explain why male lions evolved their trademark mane. It probably doesn’t help in stalking and hiding from prey but helpful at intimidating rivals and protect the neck while fighting to defend the pride

  10. dlr says:

    The problem isn’t so much low protein as low fat. Humans on a vegetarian, or mostly vegetarian, diet crave fat not protein.

  11. Art Mooney says:

    I think impulsivity is positively selected in males although the cost is high (incarceration, alcohol, drug use, car accident and suicide rates)

    When I was a kid I asked my mom when only young men were in the military (at that time). She said it was because young men don’t think about the consequences of their actions and that made them brave on the battlefield.

    The discussion of women in the military always centers on physical strength and someone trying to prove that women can make great machine gun A-gunners, you know, because they can carry a barrel bag and a hundred pounds of 50 cal ammo link. But in my experience, the real deficit women face in a combat zone is that they are not mentally adapted to any aspect of combat whatsoever.

  12. John Melon says:

    In groups like the Bushmen, women produced most of the calories…

    Why is this, exactly? It can’t be that the men aren’t capable of gathering plants and digging up roots, I bet they can do it a lot better than the women. The men must consider it to be women’s work and prefer to go hunting. The problem is that there aren’t many animals to hunt in the crappy habitats these people are living in nowadays. Prehistoric populations lived in more fertile habitats with more animals to hunt and the men would have brought home more meat than they do today.

    • Ziel says:

      “gathering plants and digging up roots, I bet they can do it a lot better than the women.”

      Women have finer color discernment, perhaps an advantage in spotting ripe fruits, avoid poisonous plants?

      • crew says:

        Women have finer color discernment, perhaps an advantage in spotting ripe fruits, avoid poisonous plants?

        Is this absolutely correct?

        I know that in new-World monkeys color vision is generally restricted to females.

        Also, there are a small number of tetrachromats among human female (<1%), but except for males with colorblindness (~8%), males and females should have exactly the same color discernment.

        However, maybe I am wrong.

        • dux.ie says:

          https://en.wikipedia.org/wiki/Tetrachromacy#Humans

          “””In humans, two cone cell pigment genes are present on the X chromosome: the classical type 2 opsin genes OPN1MW and OPN1MW2. It has been suggested that women (who possess two X chromosomes) could possess multiple cone cell pigments, perhaps born as full tetrachromats who have four simultaneously functioning kinds of cone cells, each type with a specific pattern of responsiveness to different wavelengths of light in the range of the visible spectrum.[20] One study suggested that 2–3% of the world’s women might have the type of fourth cone whose sensitivity peak is between the standard red and green cones, giving, theoretically, a significant increase in color differentiation.[21] Another study suggests that as many as 50% of women and 8% of men may have four photopigments and corresponding increased chromatic discrimination compared to trichromats.”””

          The men could be human chimera.

  13. Where do pastoralists fit into this? Especially horse mounted folks.

  14. Greying Wanderer says:

    yes, sexual selection as an extension of specialization selection makes sense

  15. G.M. says:

    Would like to propose a topic for future consideration by GC & his community: group selection. Is it real? Is it then particularly important in humans? Are we yet able to show convincingly that genes promoting senescence have been selected for on that basis in various species, & that this in itself is evidence of group selection?

    • gcochran9 says:

      HAs group selection been an important force in humans? No.

      Has it selected for senescence? Not in humans.

      • Airgap says:

        Has there ever been selection FOR senescence (group or individual), as opposed to selection for some other trait with the side effect of senescence, in any organism? Could we even tell?

      • c23 says:

        What about conquest of one group by another group followed by some degree of genocide, which happens all the time? Does that not count as group selection?

        • G.M. says:

          Thx for the replies, GC et al. To Airgap’s point, yeah, it’s probably tough at this stage to say with confidence that there has been selection for senescence per se, but I am not too up on the literature & wonder whether the case has been refined at all post-gene sequencing.

          To c23’s point, yeah, it makes sense to me that when the large-scale thighboning starts (e.g. Rwanda), it is not only the fitness of your genes that are being selected on, but the relative fitness of your group.

  16. Gord Marsden says:

    The 40 % strength advantage of testosterone on muscle fibre. The water cooled body ,sweat ,rather than radiate female style, the larger nasal passages for airflow, and a natural rage especially at younger ages, and the ability to empty the thoughts and singular concentration are all built for the hunt traits.

  17. carol2000 says:

    “It should not simply be assumed that the exclusion of women from hunting rests upon ‘natural’ physiological differences.”

    True enough. The smart way to hunt is to wait in ambush at the water hole. The kid(s) could stay home with grandma and grandpa.

  18. Eugine Nier says:

    I was looking for an intelligent discussion of this question – but I ran into this and couldn’t force myself to read further: ” It should not simply be assumed that the exclusion of women from hunting rests upon “natural” physiological differences. ”

    True in the sense that the physiological differences evolved due to the exclusion rather than the other way around.

    • gcochran9 says:

      Which is why male gorillas are so much stronger than females. Look, there was sexual selection for greater male strength before our ancestors ever made a tool. That pre-existing difference probably was a basis for job specialization based on sex: after a while you have both things going on.

  19. Garr says:

    Are male inclinations and preferences (e.g. for hunting-type activities) coded for on the Y chromosome and then they somehow overrule the complementary feminine inclinations and preferences (e.g. for gathering-type activities) that are coded for on the X chromosome?

    I’m curious about how this works because certain personality-traits do seem to be inherited from both parents, but sexual personality-differentiation would have to require some kind of if-male-then-into-hunting, if-female-then-into-gathering mechanism.

  20. Janko Raven Johnson says:

    Doc,
    Have you looked at, written on James Scott’s work, especially Against the Grain? Found some youtube videos of a couple of his talks and thought I would love to hear your take. Thanks!

  21. Spencer says:

    Cultural anthropology textbooks say the darndest things! So cute.

  22. gwood says:

    I think that men’s superior 3d visualization ability comes from throwing weapons, but I don’t know how you’d prove it.

    • Jim says:

      It’s probably pretty difficult to prove anything in evolution. One can only observe that a trait is biologically useful and infer that possession of the trait lead to more offspring. In the case of 3d visualization it seems obvious that it’s a useful trait to have if you’re trying to hit a monkey in a tree with an arrow.

  23. Citizen A says:

    Simply amazing how little academics get outside their tower. All of these stupid feminists should spend some time in a poor area junior high school. The fear of the female teachers is obvious, and palpable in dealing with 13 year old boys, because they have real experience in understanding that even immature 13 year olds are stronger than they are, and are potentially capable of rape.

    Reality does not give a crap about how much dogma you have- or we could start talking about how these women should just worship those little buggers LeTourneau style. I do find it interesting to watch the sociopathic development of a typical tribe, based almost entirely on physical ability to fight that begins at approximately 11 years old, and continues until they accept pacification (civilized restraint) or join real gangs. Lord of the Flies is real, and takes place every day in the more out of control schools in your area. Conversely, the schools in a higher socioeconomic strata remove the ones that don’t accept civilized behavior at a faster pace- thus civilized restraint becomes a smart response, even from children that would act out in an environment that tended to be more violent in total nature.

    My 2 cents.

    But, from what I have seen, the biggest problem is hiring fresh, young, inexperienced suburban women who are filled with the nonsense that drives Greg nuts. I especially liked the one that thought all of the kids in her classroom could be reasoned with, and would respond in a fairly logical manner. Way out of her knowledge base when the parents totally ignored her entire discussion points at the p/t conference and said, “Well, dey gonna pass cause dey here, right? So what if they act out, just smack ’em.”

    And off they went.

    It is entirely unPC to admit a large segment of our population isn’t just left behind by the schools, but basically nonfunctional with regard to anything past 6th grade in the suburban school.

    One of my friends said Idoicracy is here, and having more children than you do.

    • Jim says:

      Quite a few years ago I read of an IQ study of children in the Baltimore ghetto. The average was 75. The only thing I can think to do is to try to discourage the reproduction of these populations perhaps paying them a cash sum in return for undergoing an operation to render them infertile.

  24. harriettubmanagenda says:

    Sex related occupational specialization, sex-related differences in olfactory sensitivity, and multiple intelligence: women smell better, the better to locate edible roots. Maybe the answer in the progressive matrices test is “the triangle with the two dark circles and empty square inside” is correct if you’re visual (narrow IQ) but “the one that smells like a banana” is correct if you’re olfactory. Olfactory sensitivity and olfactory memory are part of nervous system function (“broad IQ”). IQ tests were designed to predict success in school. Maybe they’d test for different aspects of nervous system function if the target schools were cooking schools.

    • What edible roots does one locate by smell? Apart from garlic and its relatives, which could be found by their shoots anyhow.

      • harriettubmanagenda says:

        Truffles.
        I know, they’re not roots. Anyway, for whatever cause, women smell better. Perhaps superior olfactory sensitivity evolved in women to protect babies in utero from dangerous food contaminants. That’s by the way. We do not count a lot of nervous system function, such as olfactory perception and olfactory memory, as “intelligence”, and yet if we saw someone navigate successfully with these abilities where we could not, we might well call the result “intelligent”.

        • Jim says:

          Women in general have more acute senses in general not just olfactory. For example they generally can hear fainter sounds on average compared with men.

          While the neurological processing involved in sensory perception is no doubt extremely complex it is not what most people mean by “intelligence”. Similarly the enunciation of human speech is the most complex neuromuscular activity in all of biology but nobody gets credit for being smart just because they can speak their native language. The ability of humans to walk with a skeleton very poorly designed for walking is a biological miracle but the ability to do so is not considered to be a sign of exceptional intelligence.

          • harriettubmanagenda says:

            Awwww, shoot. No high five for the puns “smell better” and “broad IQ”. You guys are too serious.
            “Is not considered a sign of exceptional intelligence”, unless you’re Jared Diamond, perhaps.
            Maybe if you’re lost and hungry, you will appreciate the skill of the aboriginal who keeps you alive and leads you out of the jungle or the desert. You may attribute his ability to do so to his access to sensory information and memory to which you have no access. Call it whatever you like.

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