Are humans inherently monogamous?

Great Debates
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This thread is a desperate attempt to discuss something that doesn’t involve Bush, God, or homosexuality (or all 3), so please avoid mention of all three. For the sake of simplicity, this thread is assuming that there is no divine presence guiding anything, and we are how we are by evolution. Please read the whole post before replying, I have an important caveat at the bottom.

Anyway, the topic of discussion is the monogamous nature of the animal, humans. I’ve heard scattered arguments on both sides (that we are monogamous and that we aren’t). Human nature seems to be wildly random in this type of thing; some are strictly monogamous, some strictly can’t be.

From an evolutionary point of view, the long duration of rearing a young human pretty much requires the presence of a male provider (or males - in either a polygamous or a tribal sense) (my use of the term “male provider” is not to be taken in a modern social/political context, but an evolutionary one). For the man, he may have the best chance of passing on his genes if he has one wife and guards her closely, or if he spreads his seed around as much as possible, trusting that another man will care for the youth. Similarly, a female may have either a close relationship with one man and have security, or mate with many. Human females are rare in that they conceal ovulation and don’t go into periods of heat, which may or may not have important evolutional reasons (that is a debate in itself).

Within our branch of zoology, our close relatives are dissimilar. They either mate infrequently but monogamously, work as a pack, or have other machanisms. In the larger animal kingdom, it is rare for a monogamous relationship to exist, which is seen mostly in sea birds (and then, even they sleep around).

Adding to the complexity are the human social traits, which can’t be compared to anything in the animal kingdom. On top of that, we are subjective analysts of this, being humans and members of a society that almost exclusively practices technically monogamous relationships. Additionally, we seem to be unique in regarding reproduction as fun instead of a necessity done only when the time is right.

For my take on the issue, I think that humans are mostly monogamous, but have the same tendancies of the sea birds to cheat whenever possible to enhance chances of reproduction. I say mostly monogamous in the sense that there are virtually no animals that are totally monogamous - they mate monogamously by vicinity or for protection, and even then, as with humans and sea birds, they “cheat” frequently. I believe that this cheating is a side effect of our evolutional development.

So, there are the questions and issues with the statements I made above, plus the discussion of correlation and causation between our physiology, genetics, and evolution with our social structure.

And all of this is completely leaving out emotions, which are a whole nother story, along with how we evolved such complex emotions and what function they serve evolutionary-wise. But please avoid bringing emotional-based examples up. Make another thread for it, maybe. One could make the argument that exclusing emotion makes this discussion invalid, since emotion plays such a strong role in seual relations, but defining and accounting for it is unrealistic.

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I think if you look you’ll find many threads that are not directly related to Bush, God, or homosexuality. But United States policy, the ultimate nature of the universe, and the nature of humanity are pretty popular topics, so don’t be surprised if any of the topics mentioned in your OP get brought up a couple of time (or even derail the thread).

On to the topic at hand. It turns out that there’s a loose correlation between sexual dimorphism (the difference in relative sizes between males and females of a species) and behavior in mating. When the male of the species is bigger than the female, relationships tend to be polygamous. When we compare ourselves to other mammals, we find our males are somewhat larger than our females, but not to the degree that is present in some other species (seals, gorillas, etc.) This might indicate that mating in our history tended towards monogamy or some males having small harems.

Similarly, testis size is related to the mating behavior of females. In species where the male has larger testes, the female tends to mate with multiple males. In this regard, we fall slightly below the “average” testis size vs. body mass curve, indicating that it is unlikely that polyandry has not played an overly significant role in our evolution.

Given this data, a safe conclusion seems to be that both monogamy and polygyny could have been normal. Of course, none of this serves as any justification for any moral or political beliefs. Culture is also as big a factor in how we act as genetics is, and we have the power to, in many cases, overcome our genetically influenced personality traits.

All data in the above post was taken from Richard Dawkin’s The Ancestor’s Tale, in The Seal’s Tale, pg 203-11.

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Looking at some other species, it may be that males have a tendency to stray, or to try and collect a group of females. Human males seem to be wired the same way. Even those who don’t play the field will still look. Human males gravitate toward competition - football, boxing, and other macho things. Male animals bludgeon each other with horns, antlers, or fangs. From the male point of view this makes sense. It ensures that the larger, stronger, more dominant male can collect a harem and spread his genes around among many females. So, if one or a few get devoured by white sharks or giant cave weasels, his lineage still has a chance.

The female is on the lookout for a healthy male who can provide for her and the offspring and protect the herd/pride/pack. Size and strength are signs of health and suitability. Aggressiveness means he will defend their territory and feeding grounds. If she and her mate can protect and feed their young, her genes get passed along. If there are other females in the group, then they can share the effort of hunting and caring for the offspring. Lions and wolves do this - one mother and lots of “aunts”. It works for them. She will stay with the male as long as he serves a purpose. If a stronger male takes him out, she switches loyalties. If he gets too “uppity”, she and the other females beat the crap out of him and go shopping for a new “husband”. Lions and wolves do this.

So, while it is not completely monogamous, it is not completely the opposite. Both genders have a similar agenda and are useful to each other. Both have ways of getting what they want, to the benefit of both.

Of course the above verbal diarrhea does not apply to a mantis or spider. They sidestep the issue by devouring the male after he has served his purpose.

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In the short term, most of us are. Falling in love is instinctual behavior, and people who are in love don’t generally have any interest in sleeping around.

But in the long term, probably not.

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Very nice post, Dr. Love, I had forgotten those correlations, but I have a few other sources that agree with them. As I recall, testes size in pygmy vs. normal chimpanzees is a great example of how it correlates…

An interesting question; evolution never ends. May I hypothesize that humans were merely in the process of transitioning to one or the other system before we evolved speech and the social practices that accompanied the Leap Forward?

In either case, I wonder what effect our social practices have on the future evolution. I hope you haven’t gone to bed yet and can reply :slight_smile:

And I agree about no justification for social practices; the point of this thread is academics of evolution, not justification of human behavior.

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the following study heavily suggests that genes play a large part in determining how promiscuous one is. though done on birds, the study should still have strong implicaitons.

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Well, many species are monogamous for periods of time, then switch partners for various reasons later.

Hm. Falling in love is instinctual? Hm. Let me think that over, I’ll reply to this later.

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Thanks, well, that certainly makes sense, evolutionarily speaking. Kinda scary to know that you may be more likely to cheat given your genes though.

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This is overgeneralisation on a number of levels.

First of all, love and sexual attraction and behaviour are not strongly linked in all individuals, and when they are, they aren’t always linked in the same way. (I know people for whom “people they love” are a subset of “people they’re sexually involved with”; I know people for whom the opposite is true.)

Also, falling in love is not something that removes the capacity to do so again from all people. I know people for whom this is the case – having one healthy relationship shuts down whatever evaluations they make to locate another mate. Other people may well fall in love again while in love with an established mate; at that point they need to make decisions about their behaviour, including sexual behaviour. There is a cultural presumption that love-and-relationship is the same as a commitment to monogamous sexual behaviour; there are any number of people who do not include this in their relationship agreements, or who have chosen to explicitly remove that agreement from their agreements when one of them wants another mate.

If someone is one of those folks who is naturally monogamous – who doesn’t at any level evaluate whether other people will be good mates when they have a satisfying relationship – my experience is that it’s difficult for them to wrap their minds around those people who don’t have similar emotional triggers. The presumption is something like, “Oh, when you find the right one, you’ll stop.” At the same time, this causes tremendous damage to some relationships when one party falls in love again – and presumes this is because the previous partner was deficient, otherwise that emotional toggle would be shut down. Shazam, you have serial monogamy of the most heartwrenching kind.

Similarly, people who have varying levels of nonmonogamous agreements with their partners run into the same sort of conceptual gap; there are a lot of people who can’t conceive of a relationship that doesn’t presume exclusive use of emotions or genitalia.

A lot of people in the beginning of relationships experience a level of obsessive euphoria about that relationships – some folks call it New Relationship Energy, I call it ‘the pink fluffy stupids’, a friend refers to it as “Bob hates peas.” (Derivation of that: “Oh. You’re having peas for dinner? Bob hates peas.”) The impression I have is that this euphoric period is often mistaken for love, and when it wears off, the people involved wonder why everything isn’t easy, hearts, flowers, and smooth sailing, and eventually seek the next relationship to sink into the Land of the Lotos Eaters with. If “in love” is used to mean that energetic period, then that doesn’t seem implausible – it’s obsessive, after all. But I wouldn’t consider that “love” at all.

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Voles are mammals, not birds. Presumably even more implicative.

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Which way do you think we were moving? I don’t think we have a lot of data on our ancestors about their sexual habits, but I could be wrong.

IANAEvolutionary Biologist, but if I had to guess, I’d say that the main change to expect in our evolutionary future is greater genetic diversity. We’re already a pretty homogeneous species as it is, genetically speaking, modern society has lessened many of the selection pressures of the wild, and our population has been growing steadily larger for a long time. Our criteria for sexual attraction are actually fairly diverse, so sexual selection is unlikely to get out of control (think peacock). This all seems like a recipe for gaining greater genetic diversity as a species. What will this do to our appearance? Your guess is as good as mine. Perhaps as our societies grow closer together, many will lose some of the distinguishing features of the “races.” Will humans in the future be different from us? Probably, but culture and technology will be the significant factors in that, not anything evolution did to us.

Rereading that, it diverges from the main topic of the thread a little bit. The main point is that I doubt our mating practices will have a significant impact on our long term future.

True, but sometimes these things have to be said to avoid confusion.

feldman’s article is interesting. I didn’t know we could use viruses to genetically engineer living animals. Maybe questions like the OP’s will one day be moot, since we’ll be able to change our “inherent” behavior.

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I think your sentence more or less sums things up… and I’d say humans are a bit serial monomgamous. We tend to see relationship breaking up after sometime, a little cheating on the side.

Also “dating” and courtship is a enormous expenditure of resources and time… we wouldn’t have survived if single men had to keep up this kind of thing. (I’m currently beggining to date and its a lot of money we spend !) Being monogamous has its advantages… stability, security and splitting work. It makes evolutionary sense to become a couple… as well as it does to cheat a bit in order to get in a few more offspring.