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ResearchBlogging.orgThis Wednesday question (or “wondering Wednesdays,” or something else witty and alliterative. Suggestions please) comes from Colin who asks

Just wondering if there is evoanth suggesting hominids are monogamous creatures or monogomy just lies on the spectrum of dispositions?

In case you don’t feel like reading through the second EvoAnth (Colin, you’re meant to capitalise it) post in two days I’m just going to give you the answer right now: the latter. There’s nothing which suggests that humans are meant to be monogamous.

This is true regardless of what perspective you view it from. For starters you could play the numbers game. Whilst most people today are monogamous this is due to the success of a handful of pro-monogamy cultures. As such you couldn’t really tell if monogamy was typical or there are just large a-typical cultures distorting the results. Europe and the USA, for example, make up over 1/7 of the worlds population and are almost completely monogamous (as in the people inside it are, not those two regions only love each other). Thus they could distort the results of any “head-count” quite considerably.

A better way to count it is to make all societies equal and measure how many societies are monogamous rather than how many individuals. When you count it like that you wind up with 85% of human societies practising polygamy of some description, so monogamy is far from the norm for our species. Indeed, 85% is the number for polygyny (one man having multiple wives) rather than polygamy as a whole. Polyandry (when women are the lucky ones) is rarer, granted, but still exists. As such 85% is a low-end number.

Alternatively you could look at it biologically. Perhaps we have some hormone that prompts lovey-dovey feelings, but only when exposed to the same individual. Surely that would be a pretty sure indication that hominins are meant to be monogamous. Of course if such a thing were discovered I’m not sure whether it could be used to demonise non-monogamous people. Being different isn’t something we should be automatically intolerant of, especially if that is the product of their biology.

However, my caveats against discrimination are somewhat moot given that we have yet to find this lovey-dovey hormone which only responds to a single individual. Neurobiologists are aware of a range of hormones associated with affection and attachment in relationships (although they still don’t have the complete picture). These include vasopressin and oxytocin (the famous “cuddle hormone“) which are released during intimacy and work with the dopamine system to make bonding with someone a rewarding experience (dopamine being the brains reward system).

There’s also testosterone (whose involvement people don’t know much about) and several others, including serotonin. This chemical appears to be associated with happiness, yet contrary to what you might expect it actually decreases during the early stages of a relationship. This may be associated with how you idealise a partner during those early days. Such a decrease is also associated with OCD, leading to the amusing quote from the aforelinked paper.

Indeed, early stages of romantic love show similarities to OCD, including symptoms of anxiety, stress, and obtrusive thinking….although we should keep in mind that OCD is a Diagnostic and Statistical Manual of Mental Disorders version IV (DSM-IV) disorder and the early stage of romantic love is not.

Again, there’s nothing about any of these hormones that limits them to only applying to only one individual. Serotonin, for example, is also linked with food consumption yet you can enjoy two dishes. Oxytocin is also associated with breast feeding yet a mother can love two children. There’s no need to limit these chemicals to only allowing monogamous relationships.

That said, some studies have been done which show a relationship between monogamy and oxytocin in voles. However, these aren’t comparing monogamy with polygamy but whether a monogamous vole will have an “affair” (it won’t if it has more oxytocin) or they reveal that a monogamous species has more oxytocin receptors than a species which has more “affairs.” In other words they’re measuring monogamy versus promiscuity rather than monogamy versus polygamy. As such they can’t really applied to this situation and so the presence of oxytocin does not mean humans are meant to be monogamous.

Darker patches indicated more oxytocin receptors for a monogamous vole (left) and promiscuous vole (right)

So there you have it. Humans aren’t supposed to be mongoamous. However, that shouldn’t be construed to suggest we are meant to be polgyamous. Instead these are just both parts of the wide spectrum of human mating strategies. Neither are really “correct” any more than a particular hair colour is right. It’s just natural human variation.

A. de Boer, E.M. van Buel, G.J. Ter Horst (2012). Love is more than just a kiss: a neurobiological perspective on love and affection Neuroscience, 201, 114-124 DOI: 10.1016/j.neuroscience.2011.11.017
Henrich J, Boyd R, & Richerson PJ (2012). The puzzle of monogamous marriage. Philosophical transactions of the Royal Society of London. Series B, Biological sciences, 367 (1589), 657-69 PMID: 22271782
THOMAS R. INSEL, LAWRENCE E. SHAPIRO (1992). Oxytocin receptor distribution reflects social organization in monogamous and polygamous voles Proceedings of the National Academy of Sciences, 89, 5981-5984 DOI: 10.1073/pnas.89.13.5981
Ophir AG, Gessel A, Zheng DJ, & Phelps SM (2012). Oxytocin receptor density is associated with male mating tactics and social monogamy. Hormones and behavior, 61 (3), 445-53 PMID: 22285648

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40 Comments

Colin Mackay · 20th June 2012 at 11:07 pm

Gotta luv having the ability to consultant an anthropologist, what a world is emerging:)

    Adam Benton · 20th June 2012 at 11:59 pm

    Don’t get penisey kid; anthropologist in training.

      Colin Mackay · 21st June 2012 at 8:27 am

      LOL In training…close enough. Kid, I’m flattered

clyte · 21st June 2012 at 1:25 am

Just goes to show…if you narrow your question enough, you can create any slant you wish. It’s my understanding that polygamy was an option in many cultures – for wealthy men (sexual variety being a powerful aphrodisiac). However, the overwhelming majority could afford only one wife, so most humans have lived in pair bonds…with a bit of cheating on the side.
More interesting questions might be, are romantic bonds fragile strictly due to biology, or is our behavior today making them more so? Or, is individual wellbeing served by steering for a pair bond (assuming no rewards from complying with cultural pressure)?

    Adam Benton · 21st June 2012 at 2:01 am

    Well monogamy is very beneficial for a female since they gain lasting investment by another and have little to gain by repeated matings. On the surface it can seem to be less than beneficial for males since they do have quite a bit to gain by having multiple partners. At the same time there are also some costs such as decreased paternity certainty, increased competition, increased STI risk etc. Without trying to state the obvious, when those costs outweigh the benefits then monogamy will be good for them and current models are basically trying to work out situations when that would be the case. “The puzzle of monogamous marriage,” linked to from the citations, is an example of one such effort.

    As for romantic bonds it would be interesting if scientists could work out whether the neurological basis for affection has undergone any recent evolutionary change. It may well have, with lower oxytocin being correlated with promiscuity, thus that phenotype would’ve been spread throughout the population. However, that seems like a bit of a stretch of reasoning and I think it’s more likely that there has been little change to the underlying basis for relationships and it is actually the result of epigenetic factors.

    Or it might be relationships were just this shitty the whole time and only recently are people getting comfortable acknowledging that. 😉

Jim Thomerson · 21st June 2012 at 3:37 pm

In one of his Natural History columns Steven J. Gould discussed a study of relationship between male and female size and breeding systems. Large male and small female gives a system where one male mates with many females. Large female and small male gives a system where females mate with many males. Humans are near the middle of the spectrum. As I recall, size differences between human males and human females predicts a mating ratio of 1.28 females per male.

    Adam Benton · 21st June 2012 at 7:02 pm

    There’s little in the natural world that screams the answer. I continue to be amazed by the ability of scientists to work around this fact.

    Is this column available somewhere?

neuroecology · 22nd June 2012 at 6:42 pm

I guess I don’t understand what you mean by ‘supposed to be’. Isn’t it a bit like asking, are humans ‘supposed to be’ heterosexual? Some are, some aren’t?

I’m curious why you decide to normalize for number of societies rather than population, aren’t you using a historical anomaly either way? There used to be many different societies within the polity that is now Germany, UK, etc, that were later subsumed by the nation-state. How do we ‘count’ those?

Perhaps the odds of a society being polygamous is related to the lifestyle; low-calorie versus high-calorie, sedentary/pastoral versus hunter-gatherer, etc. And perhaps that leads to a feedback cycle modifying, say, oxytocin level preferentially increasing monogamous bonding?

    Adam Benton · 23rd June 2012 at 11:17 am

    Or perhaps, are humans supposed to be bipedal? There are some traits we’re “meant” to have and others which can contain some variation. My question was really whether it was one or the other. Whether there’s some aspect of our physiology that indicates monogamy is the natural state for humans or whether its a continuous trait with variation.

    I went via society because that’s what I could find data on. Whilst I won’t pretend I looked at every paper ever (so if you know of studying it via population please tell) but I did have a decent look at the research and the only figures I could find were measuring it via society. I believe they included some past societies as well, but can’t check as am away from where I have access to the paper.

    That would certainly be an interesting way to break down things and not an implausible proposition either. Lifestyle appears to have an effect on a range of different societal factors, so maybe it has an impact here. Many Inuit, for example, use cognatic inheritance because that gives them access to both their mothers and fathers resources which is useful in the harsh northern environment they live in.

Joachim · 24th June 2012 at 6:58 pm

Wednesday Wit(ti)ness?

Jim Birch · 26th June 2012 at 5:40 am

Monogamy might be a successful habit for a society in that it allows a higher level of cooperation between males since mating competition is circumscribed and formalised. Maybe 85% of human societies practise polygamy but the monogamous ones may do better – and grow – since aren’t engaging in semi-continuous warfare over females. This may or may not benefit specific individuals but overall the amount of conflict is reduced. This is similar and related to the general benefit that accrues when individuals accede a monopoly on violence to the state and rely on law and custom to settle disputes.

Like all such arrangements, a prisoners dilemma situation occurs. An individual will benefit from cheating so a variety of mechanisms are required to limit it. These can be built into the wallpaper of social norms and trust relationships but can often include the use of a degree of force such as in this Tim Buckley song:


Well now he finally walked in
And Lord that man filled up the doorway
Well he grabbed me by my throat
And he bounced me down the stairs
And Lord I swear, he broke every bone in my body
But it was worth every second that I was there
Cause she would whisper to me…

    Adam Benton · 3rd July 2012 at 1:17 pm

    However humans (and our hominin ancestors) have very little sexual dimorphism. This is consistent with limited sexual competition so I’m not convinced that even non-monogamous societies would have significantly more violence over mates. We’re just not physically built for it.

    As for cheating, this is one of the reasons I thought that monogamy was the most common form of human social system prior to researching this post. Being so “strange” monogamy has attracted more research than other mating systems so most papers on human mating is about monogamy. Thus it left me with the impression that monogamy was the most common when in reality it was in the minority.

    Most of that work is basically trying to work out situations when monogamy would be viable. “The puzzle of monogamous marriage,” linked to from the citations, is an example of one such effort.

    Artem Kaznatcheev · 5th July 2012 at 2:12 am

    This is a cute idea. I would really like to see a (evolutionary) game theoretic account of this. One of the underlying ideas is something deeper than just the particular question of monogamy. If you have some groups that are better at increasing their numbers while remaining one group, and other groups that are better at splitting off into smaller groups and thus making group-children, then this throws a fun model into the recent group-selection debate. How should I judge the ‘success’ of a group? By the number of individuals that belong to the group, or by the number of new groups it spawns?

      Adam Benton · 5th July 2012 at 11:05 am

      When I was writing about how there is a bias of large monogamous cultures I did wonder if perhaps there was a link. Any such investigation would certainly be very interesting and might go some way to explaining why monogamy developed given its seemingly paradoxical nature; which is the question a lot of research is trying to answer.

R. K. Sepetjian · 27th June 2012 at 2:02 am

“There’s nothing which suggests that humans are meant to be monogamous.
This is true regardless of what perspective you view it from.”

False.

“And he answered and said unto them, Have ye not read, that he which made them at the beginning made them male and female, And said, For this cause shall a man leave father and mother, and shall cleave to his wife: and they twain shall be one flesh?” Wherefore they are no more twain, but one flesh. What therefore God hath joined together, let not man put asunder.” Matthew 19:4-6

    Jim Birch · 27th June 2012 at 2:25 am

    On the other hand, Jesus refused to condemn the adulterer so he appears to be a bit ambivalent on the point. Taking all his statements together he seems to be implying that monogamy is his recommended practise, for those who can can manage it, but if you can’t, you can be forgiven.

    Of course, all this is in the realm of unverifiable narratives so has zero value for science.

      R. K. Sepetjian · 28th June 2012 at 7:07 pm

      Adam stated, as I quote above, that no perspective values or promotes monogamy, which I roundly falsified. You are not required to like or agree that I falsified it, yet, it is falsified nonetheless. This falsification also does not require that the Bible even be true or scientific to satisfy the challenge.

      Your commentary betrays a level of biblical illiteracy that demonstrates you should not be commenting on Scriptural matters.

      I gave a direct quote from Jesus. You gave your (incorrect) interpretation on a separate passage. That does not mean that there is a contradiction between the two nor does it mean that Jesus is ambivalent on the topic.

      Correct hermeneutics on the passage you mention (John 8:1-11), reveals that the crowd who brought the woman to Jesus, was trying to set him up, which they attempted several times. For starters, they only bring the woman and not the man who is equally guilty and deserving of stoning under the Mosiac Law. Then, they pose a question to Jesus that seemingly, no matter how he answers, they have him trapped by alienating either Jewish or Roman Law. If Jesus says, ‘Don’t stone her.” They would accuse him of violating the Jewish Law and advocating against what Moses taught. If Jesus said, “Stone her.” , they would immediately run to the Romans and charge Jesus with insurrection against Rome by advocating against Roman Law. John 18:31 demonstrates that under Roman Rule, the Jews could not lawfully execute anyone. (Then take him away and judge him by your own law,” Pilate told them. “Only the Romans are permitted to execute someone,” the Jewish leaders replied.)
      Jesus then makes the following statement after their repeated questioning:
      “Let any one of you who is without sin be the first to throw a stone at her.”
      Since the eyewitnesses were required to participate in the stoning of those they accuse, and since all the accusers left the scene as Jesus knelt and wrote in the sand, there were no longer any charges left to levy. This is what is meant by Jesus’ question to her:

      “Woman, where are they? Has no one condemned you?”

      “No one, sir,” she said.

      “Then neither do I condemn you,” Jesus declared. “Go now and leave your life of sin.”

      If the supposed “eyewitnesses” were not going to stone her, WHY WOULD Jesus, who was not there and had nothing to do with the charges, alone condemn her?

      Jesus ambivalent?

      Jesus declared. “Go now and leave your life of sin.”

      He didn’t say, “Yeah, monogamy’s cool if you can manage it.”

      Finally, not only is the New Testament NOT an unverifiable narrative, The New Testament is the MOST HISTORICALLY RELIABLE Document in the history of the world. Do a little research on how historical reliability is established before making absurd statements.

      Adam Benton · 3rd July 2012 at 1:44 pm

      And in an ironic twist that damages both of your cases it must be remembered that it has been argued this passage is not part of the original gospel. It is absent from many early copies of John and when it does appear is often marked in such a way that suggests it is an interpolation.

        R. K. Sepetjian · 9th July 2012 at 1:51 pm

        Adam,

        One of my specializations is ancient text families and the manuscripts which comprise them. Some digging would demonstrate that John 7:53- 8:11 belongs in the passage.

        1) Continuity Problem
        For starters, if you pick up in John 8:12, you have Jesus addressing “they” and “them” which has absolutely no connection to the previous paragraph (John 7:52), neither are the same people pictured; Nor do we know who the “they” are, so something is definitely missing if you remove this passage.

        2) Consistent with the rest of Scripture

        3) Consistent with the nature of Jesus

        4) Consistent with the design of this Gospel
        John 5 contains Miracle/Event and then discourse
        John 6 contains Miracle/Event and then discourse
        John 7 contains Miracle/Event and then discourse

        If you remove the opening event from John 8 and pick it back up with John 8:12, you jump right into the discourse.

        5) Documented in early church records and Apostolic constitutions.

        6) Authenticated by early church fathers, Jerome, Ambrose & Augustine.

        Therefore, my case and point remain undamaged and God’s plan for us still includes monogamy.

        Adam Benton · 9th July 2012 at 2:24 pm

        But the adulterous tale also ends with Jesus being left alone, the mob leaves and he promptly sends away the woman. The next passage starting with “they” is a continuity issue regardless of the inclusion of this tale.

    Adam Benton · 3rd July 2012 at 1:34 pm

    When deciding whether a quote from a famous individual should carry weight I like to employ the Captain Picard technique*. If Picard, of Star Trek: The Next Generation, said that same quote would it still be meaningful?

    If yes then there is clearly something to the statement since it is independent of the credentials of the speaker (which can be disputed). If it is not then it’s little more than an assertion and so perspectives based off that statement do not get to be considered until the foundation of that assertion can be verified.


    *This is a modification of the Captain Kirk method, employed by Russel Glasser of AETV fame. I use Picard because I like him more than Kirk

      Pyper1384 · 12th September 2012 at 8:07 pm

      Adam, I love the Captain * method. 🙂 This is a great point to this particular response.

        Adam Benton · 12th September 2012 at 8:15 pm

        As I said, all credit goes to Russel Glasser.

fieara · 4th July 2012 at 10:32 pm

I’ve seen three scientific documentaries on this, and they did experiments during the documentary; all experiments and documentaries proved both genders are biologically wired for polyamory and promiscuity (casual sex) to maximise breeding potential and the best genes for our offspring. We are biologically wired against incest, and to be attracted to someone carrying different genes that protect from disease (so the resulting offspring will be protected from many diseases). Interesting post.

    Adam Benton · 5th July 2012 at 12:24 am

    Bateman’s principle is the notion that the gender which invests the most in an offspring should be picky over who they mate with since just having lots of babies isn’t viable for them. Instead they should focus on making sure the few babies they can have are the best possible. As such the notion that women are also predisposed to polyamry is surprising.

    However, it is not implausible. Were the benefits to multiple couplings (i.e. having two men donate resources to the child as they both think they are the father) sufficient then it would be a perfectly valid strategy. Do you recall what the experiments were?

      Jim Birch · 5th July 2012 at 1:58 am

      We aren’t actually biologically wired against incest, we are wired against feeling sexually attracted to the people who we lived with as we grew up. Statistically they are likely to be half or full siblings. Without genetic testing, determining who is actually a sibling is tough so we have evolved to use a fairly reliable proxy. Anecdotal examples of this distinction are the sexual failure of child marriages where the female lives with the male from an early age, and the attraction between brothers and sisters who have been separated at near birth.

      Likewise, we aren’t actually wired to reproduce, we are wired to for sexual attraction – historically a good proxy – and to want company, support and protection both for ourselves and our offspring. For males, impregnating the maximum number of females is a no brainer (ha!) except that you might get killed by other threatened males or avoided by women who regard you as unlikely to support to support themselves and their kids in the long term. In a sense, human males have been “domesticated” into monogamy by female selection of characteristics like the desire to bring home the bacon and share it with her kids.

      This the realm of game theory where cheating and policing are part of the mix. A woman might slip out for some of the visibly superior genes up the track, particularly near ovulation, provided it doesn’t threaten her current support, and the male can employ a corresponding strategies to obtaining extra impregnations.

      Cultural norms like marriage that solidify the imagined of ownership of a partner into a social convention – with supporting narratives and penalties for transgression – presumably developed to counter the unease – and conflict – that the potential for all this screwing around produces.

      But, as humans with the potential for actually looking and feeling into the brain processes of mates, we seek the ultimate protection against our partners’ biological interest in promiscuity: undying true love. Which we all know can’t be faked. 🙂

        Adam Benton · 5th July 2012 at 11:14 am

        And that’s why everyone loves birth control!

        Sorry for the bad joke, I just wanted to write more than “excellent comment Jim.”

        ….

        Excellent comment Jim

Danetta.J · 11th July 2012 at 1:23 am

So do you think Bateman’s Principle applies to humans as well.?

    Adam Benton · 11th July 2012 at 2:36 am

    From what I’ve seen there is some evidence that humans do follow Bateman’s principle, although it is far from concrete. That said my reading of the literature is not exhaustive and this lack of definitive evidence could simply the result of me not finding it.

Alan · 13th September 2012 at 5:16 am

The study for ‘god evolved’: “Standard cross-cultural sample” (1980), also includes data on monogamy: more food in the environment (humidity), more fooling around! The harder one must work to feed everyone, the more monogamy. That suggests the eventual over achieving of monogamous cultures – they developed where more work was required, they got into that habit, built more and invented more as well.

    Adam Benton · 30th December 2012 at 1:56 am

    I was somewhat weary of drawing that inference given the plethora of factors that can contribute to the rise and fall of a culture. Signalling one out seemed unjustified, particularly given the lack of controls in such a simple correlation study. What if, for example, certain demographic factors influenced both innovation and mate choice?

Alan · 13th September 2012 at 7:43 pm

Let’s reflect a minute on the title of this post and the data you want to hide behind the curtain, asking us to ignore. Humans are very adaptable by design, but we were never ‘supposed’ to do anything, including survive. We have, however, seized the opportunity and demonstrated an ability to survive – those of us lucky enough and descended from those who made (on the whole) effective choices. What we were asked to ignore is that virtually all of the successful societies chose monogamy and that the large number of flexible choice societies are struggling or failing. Why do you suppose the choices of a marginal or failing society should be considered at equal weight to successful ones when we consider behavior?

    Adam Benton · 30th December 2012 at 2:01 am

    By “supposed” I mean “have a biological imperative for.” We desire to eat, breath, reproduce, develop and maintain social bonds and so forth. My question was whether there was a similar drive for monogamous realtionships; whether our biology mandates we have them. Given their ubiquity in Western society this seems like a plausible hypothesis, albeit one that is ultimately untrue.

Butt Pirate · 31st January 2013 at 4:39 pm

As I understood it, the human mating system has evolved from a gorilla-type harem system.

The theory goes that our ape recent ancestors used a harem mating system with an average harem size of something like 3 or 4. Over the past few million years the harem size has got smaller and smaller approaching monogamy but it hasn’t quite got there. It’s now at about 1.2.

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