Men and women, harems and hormones

Following a number of conversations and even throwaway remarks from various people lately that have got me wondering, I decided to investigate the extent to which our typical relationship patterns (such as monogamous marriage) can be considered “natural”, and I came across this brilliant article by David Brin.

The bulk of the article provides the groundwork for some speculative statements on the evolutionary origins of various physiological characteristics of women – which are interesting, and slightly disturbing in places – but it was this groundwork that provided some answers to my question, which I will summarise here.

There is a correlation between harem size – that is, “the number of ‘wives’ a prime male in a species impregnates during his lifetime” – and the ratio of male to female body size (bigger harems mean more competition between males, which drives an increase in their physical size). However, even in monogamous species (such as birds), where the harem size and body size ratio are both 1, males will occasionally engage in “opportunistic philandering” where this poses a low risk to them and their family. So monogamy is more a matter of devotion than strict fidelity.

I’ll just let the shock of that settle in for a moment, yes? 😯

The human body size ratio predicts a harem size for humans of about 1.1-1.4. This means monogamy does make sense for humans; however, “human males show an incredible range of motivation and behavior” stemming from a complex evolutionary history. The problem for women, of course, is that human infants require a lot of nurturing, and this fact results in competition between women for the men who are motivated to be fathers (beyond the act of conception ;)).

So, in the history of our species, men have had to compete for women (because polygamy is possible, therefore some men could miss out); but women have also had to compete for men (because there is a shortage of “good” ones from their point of view).

Not that this was any surprise to me by this point, Brin concludes that “there is no design possible for a human utopia. Whatever society we put together will at best be a network of compromises.”

The mechanisms for the inclination towards pair-bonding (falling in love, being faithful) have to do with receptors in the brain for hormones such as oxytocin and vasopressin. As I learnt from this talk a few months ago, this type of evolved mechanism is what makes us care for one another and, along with empathy, this compassion is the biological root of our sense of morality. The variation in human male relationship preferences, I gather, may be mirrored by variation in this brain chemistry.

But on the other hand, behaviour is heavily conditioned by environment (e.g. resources) and culture. This is where it gets more positive. I’m increasingly convinced that we are not only behaviourally flexible but are well-equipped, with our intelligence and compassion, to be morally creative and invent harm-reducing ways of living that go beyond the various instincts evolution has dumped us with.

Facing the truth about our natures, and de-stigmatising our less socially-acceptable motivations for a more frank treatment of them, can only help us find the best compromises and embrace them willingly.

As Brin says beautifully at the end:

“Once people of good will, both men and women, are better aware of the hand dealt them by evolution, they must almost certainly grow better at playing it.”

“For all its tragic implications, this cycle of mutual selection has meant that both genders experience much the same range of emotions during their lifetimes. True, men and women seem at times to concentrate on different priorities, which come into sad conflict in our present culture. But standing back, one can say without any doubt that both girls and boys grow up knowing what it’s like to feel the fear and excitement of initiating an encounter, as well as being the one to evaluate or choose, to accept or refuse. In most species these activities are strictly reserved for one sex or the other, but men and women both experience rejection, and each knows all the happy and aggravating phases of bonding. This may help women and men empathize with each other to a degree I would suspect is unprecedented between the sexes in nature, where males and females have little experience of each others’ ways. Those who perceive only the gulf between men and women should take note.

Finally, although we may have stumbled about blindly in our million years of feverish adaptation, and while we now find ourselves boxed in, with little hope for anything like utopia, there is no cause for shame. If we are awkward and uneven in our adaptations, it is because we are a people still in rapid flux. One cannot hope or expect that a species will be perfectly at peace with itself when it is still in furious transition from what it once was, toward what it eventually may become. The first species ever to have some control or choice about that destiny.

Compassion is the trait we may be most proud of. Ironically, it can have come from nowhere else than the bizarre story of our ancestors’ competition for reproductive success.”

This entry was posted in gender, Humanism, moral issues, morality, science. Bookmark the permalink.

20 Responses to Men and women, harems and hormones

  1. susanne430 says:

    Interesting topic. I enjoyed reading your views!

  2. We are always evolving, if we believe in evolution it only makes sense to say we can “overcome” our biological impulses.. In time even this will evolve, no? Adapting to the new ways we live and interact.

  3. Sophia says:

    Such a surprisingly moving look at the evolution of human reproduction. I wish there was a religion in which the ONLY tenant was Compassion, because I agree with Brin that it is our proudest trait.

  4. RJW says:

    Alongside size/power, the other factor in males that is selected for in mate choice by females is status. Size and power are readily visible and difficult to fake; status is harder to see, so males make considerable efforts to demonstrate status. For example, most of what David Attenborough and Billy Connolly do count as displays of status – making other people listen for long periods of time. Being a “respectable” member of the community is a more obvious display of status (and so respectability is selected for). Ditto, of course being a rebel iconoclast. Holding and displaying knowledge that others don’t is status (this one goes wrong in train-spotting).

    Male swallows with asymmetric tails breed more than ones with symmetric tails. The reason for this is that if they can survive despite this handicap, then they must be super-fit (have very good immune systems). Compassion seems to be a human variation of this same principle – demonstrating an (artificially created) handicap that the person can nevertheless cope with. [This works if you think of compassion as giving away a competitive advantage to someone in a weaker position.]

    However, after all that – the basic science behind this is usually very small effects that account for rather little of the variance. Statistically significant but not necessarily a very big part of the story.

    • Julian Adkins says:

      Hi RJW. Of course, as Sarah points out, all of this is very speculative (no one can go back to the early ancestral environment to run the experiments) but it is very interesting and plausible none-the-less. However, I did baulk at the comment you made about compassion as an example of the famous Zahavi handicap principle. The idea that compassion is primarily motivated at the biological level by showing off rather than reciprocal altruism between kin (who share similar genes) doesn’t really wash with me. One has to remember the principle of the selfish gene put forward by Dawkins and others. The Zahavi principle operates at the level of the individual, kin altruism operates at the level of the gene (irrespective of which relative it happens to be in) and therefore I think it is likely to be far more primary. I am not discounting Zahavi entirely, I just don’t think it is as influential. I realise that kin altruism doesn’t explain the wider manifestations of compassion, but I like Dawkin’s ‘misfiring’ idea to account for this. Perhaps I dislike considering Zahavi as so foundational for idealogical reasons. I don’t like the idea because it suggests that compassion is really nothing to do with caring about others for their own sake. However, I do realise that isn’t a good scientific reason for downplaying it! Perhaps none of this really matters though. We have compassion. What are we going to do with it?

      • Sarah says:

        Julian, I am certainly more familiar with the notion of compassion being adaptive because kin who share genes benefit from it. At the level of parent-offspring, this is obviously the reason for it, and that talk I went to implied that our morality on a wider scale stems from our being a family-oriented species. Clearly there are other theories that I should learn more about. I actually find Dawkins’s misfiring idea quite uninspiring actually; caring for people you aren’t related to is not adaptive so why bother? Of course there are reasons to bother, but I was bothered by questions like that when I was letting go of religion and looking for an alternative external rule book. 🙂 As you say, we are how we are, and how we got here doesn’t really matter.

    • Sarah says:

      RJW, thank you for mentioning status which I think was omitted from the article. Interesting because the stereotype is that the high-status men – sports players, politicians, celebrities of all sorts – can be the most spectacular cheaters and liars (Tiger Woods, Bill Clinton etc.). I have read elsewhere that testosterone plays a big part in that connection.

      I guess the origins of compassion are not entirely clear-cut. Maybe something else for me to look into…

      Yes, I suspect role models/social conditioning plays a much bigger part in behaviour than any of this!

  5. Julian Adkins says:


    I love the vole studies and also the stuff you have discovered by Brin on body/harem size. I’ve not heard that before. I have heard people speculating about the evolutionary advantage of opportunistic infidelity out with an ongoing monogamous relationship though. I am afraid I have no references, but have read the idea that the genes associated with male dominance (that a women might want her offspring to have) may not be associated with supportive parenting. If that is the case then it might be a good strategy for a woman to find a caring sharing kind of guy to pair bond with, and have a quick shag on the side with the alpha male 😉 I have even heard suggestion that this is where the unusual characteristic of concealed oestrus in human females comes from. I am getting terribly self conscious now though. Do you think I am just writing this to impress a pretty female reader with my knowledge in the hope she will see it as a sign of status – thereby increasing my chances in the mating game 😀 It is all a bit depressing really.

    On a more serious note, I think the vole study ties in nicely with the point I made in response to your post on Jonathan Haidt’s work. It is pertinent to the maxim that one cannot derive an ‘ought’ from an ‘is’. If it turns out that some guys are not genetically (neuro-physiologically) wired for fidelity (like the montaigne voles) should they be excused for breaking marriage vows? I think not, on the basis of the maxim just mentioned. However, whether they should take the vows in the first place is another question. I like Brin’s view of a ‘network of compromises’ being required in society rather than utopian ideals. Perhaps we need a bit more self-knowledge, honesty and relationship models (and agreements!) suited for the individuals involved rather than a one size fits all. One might think that has been going on since the 60s, but I am not so sure. The 60s were just as idealistic and unrealistic in their own way and I think that even now, there is much more we could do to encourage non-traditional and yet open, honest, responsible ways of living and loving.

    • Sarah says:

      “the genes associated with male dominance (that a women might want her offspring to have) may not be associated with supportive parenting.”

      Yes, I was just speculating something like that in another comment up there! In fact I seem to remember the Brin article describing a tendency for females to have affairs with alpha males, possibly because of this. It was all too much to take in I think.

      I think this is a topic that could make anyone self-conscious! 😆

      I remember your comment about the is/ought disconnect (David Hume isn’t it?) and I was thinking about that here too. In fact I have been reading some furious debates on Humanist message boards over the extent to which science can inform morality. One person will say that morality is best constructed by looking at our evolutionary biology to tell us what we value. Another will miss the point and say that science tells us crazy things, like, that rape is adaptive, and we are intelligent and creative enough to render our evolutionary origins irrelevant. I think both sides have a point; I think that it’s helpful to know the hand evolution has dealt us as Brin says, but that we not only can be morally creative and responsible but we should – meaning that “my brain chemistry made me do it” is not an acceptable excuse for causing hurt and harm, as you say.

      “Perhaps we need a bit more self-knowledge, honesty and relationship models (and agreements!) suited for the individuals involved rather than a one size fits all.”

      Exactly! Understanding is what’s needed, and probably secular moral education from a young age which I think there is a huge gap in the market for. Social norms can be useful but one size does not fit all as you say.

      Taking it a step further, if the guys who are not inclined to be very loving/nurturing (and perhaps some females too?) could just not become parents, which would require them being honest about this fact and others being able to discern such people and not coerce or trap them into a family, then this trait could be evolved out. Maybe that would make a utopia within reach for future generations. Crazy idea?!

      • Julian Adkins says:

        Yes Sarah, the “is” / “ought” problem was definitely put forward by Hume. I don’t know if he was the first, but wouldn’t be at all surprised if he was. What an intellectual giant! I get the impression that Western culture owes him a huge amount.
        I like your idea of evolution ridding us of guys who aren’t interested in helping raise their own children – despite the fact that I am in that group 😉 Unfortunately I am not optimistic that it will happen though. I’m getting into personal territory now, so better save further comments for an email or the next time we catch up properly 😉

  6. sanil says:

    Cool! You find a lot of interesting articles. I liked reading this and learned a lot.

    I should learn more science. 🙂 It is much more fun than I remember from my classes.

  7. RJW says:

    Compassion is, of course a red-hot topic here in Scotland, where the government (correctly in my view) released Al-Magrahi following the age-old Scottish legal code of compassionate release for terminally ill prisoners. Why was this done – and why is it supported by so many Scots?

    This instance, at least, has nothing to do with kin selection. I know that certain US senators think it has to do with reciprocal altruism – but it doesn’t as the supposed beneficiary of the reciprocal act has no relationship with Scotland (in fact they pulled out of Scotland with enormous loss of jobs 25 years ago). So neither of the regular biological explanations work. Ditto when I help an old person to cross the street safely.

    My own view is that it is Scotland demonstrating to the world it’s status as a highly civilized country. Ditto, I’m demonstrating to the world that I am a highly civilized person. You gain perceived status in that way.

    • Julian Adkins says:

      I agree RJW, the instance of Al-Magrahi doesn’t have anything to do with kin selection, but I think it is important not to mix up individual instances in the here and now with our evolutionary origins. I think they are different questions. This is precisely because we are able to take rational decisions based on abstract principles in spite of our primitive evolutionary conditioning at other levels. It may well be that judges, and indeed the general public, are doing this when they come to decisions about such things.
      The Al-Magrahi case or that of helping the old lady across the road do not pose any logical problems for kin selection augmented with ‘misfiring’ theory (although I am not apologising for these ideas). Also, I think status is very likely to be a big part of the picture – we all really care what other people think of us.
      The ‘misfiring’ idea is that compassion emotions are a biological mistake in some circumstances. That is to say that we operate on a biologically programmed heuristic which was in the interest of our genes in the early ancestral environment in which we evolved, but may not be strictly in the interest of the reproduction of the individuals genes now (in the modern environment). An oft quoted example of the misfiring idea is the fact that our biology still rewards us for having sex (i.e. it feels good) irrespective of whether we are using contraception. From a evolutionary point of view this is a ‘mistake’ or ‘misfiring’, but it has nothing to say about the morality (or otherwise) of using contraception today. Likewise, evolutionary theory may have nothing to say about the morality (or otherwise) of releasing Al-Magrahi. It may not even be able to answer the question why Judges (or even the general public) come to the conclusions they do.
      Reflecting on this more, I wonder if the misfiring hypothesis needs to do that much work in the case of compassion anyway. If kin selection can happen in the extended family, then surely it can happen in a tribe, if in a tribe then also in a species. In one sense the whole of humanity is one family. We are very social creatures, so there must be heavy selection pressures to fit into any human society wherever it is and it is reasonable to suppose that compassion is an important part of that. You could say that when you help the old lady over the road, the compassion genes in you are looking out for the same compassion genes in her. After all, humans share the vast majority of their DNA, and compassion genes may be part of the entire species inheritance. Of course, what complicates matters is that no genes operate in isolation and other one’s for dominance, selfishness and aggression may co-exist to respond to different circumstances.
      I think what I shall do (for purely pragmatic reasons) is to assume that compassion genes are out there in a big way in everyone, and my task is to get them switched on, in myself and others  Of course the corollary follows we all have the selfish, nasty ones too, and equally, the key to switching them on or off lies in the environment we create for ourselves and the habits of mind we adopt. I may have all the genes to be an Olympic sprinter, but if I eat chips and watch telly rather than training, then I’m not gonna be breaking any records. lol 
      The possibility for identifying genetic problems that are socially dysfunctional in almost all situations (autism for example) is exciting. Perhaps these could be engineered out. For the vast majority of human traits, however, I suspect the responsibility is going to lie with us to make the best of them for many generations to come.

  8. Sarah says:

    “Monogamy may not be natural, but neither is indifference to our partners’ sex lives or tolerance for polyamory.” Thank you Jesse Bering, for explaining it so clearly – it is just so reassuring to have it pointed out that our values, even the conservative religious values some people want to throw out, are completely consistent with evolutionary biology. Makes it so much less depressing. (I love Jesse Bering)

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