In his excellent post Dateonomics, our friend Taylor talks about the sociological argument for polygyny (one man having multiple wives), especially in the context of the mainstream LDS Church. Here I’d like to talk about the biological argument for polygyny.

If you assume that the main biological goal of a species is to reproduce, then – bluntly speaking – females are much more valuable than males. If a woman (or a female animal, more broadly) does not have children for whatever reason (early death, infertility, intentional childlessness, etc.), those 8 or 10 or however many children she could have had can never be recouped or recovered and the children those children would have had can never be recouped or recovered, either. It is a permanent loss to the species as a whole.

On the other hand, if a man (or a male animal) does not have children, that does not mean that there have to be any fewer children total. Any of the other males could step in for him. A man could have 1,000 children. Most women could reasonably have 10 or 15 at the most, and though there are some women who could have more, none of those outliers even fleetingly approaches the number of children an average man could have. A species is limited in its generations by the female members of that species. And yet there are a roughly equal number of men and women in the world. The result? Superfluous men. The women are not biologically dispensable, but most of the men are. You see this in other species, too. You only need one ram per some forty or fifty ewes¹, and only one rooster per ten hens².

Females being biologically indispensable is one of the reasons forced monogamy is such a tragedy. Ideally, from a biological perspective, every woman would have children. There are slightly more men than women world-wide (in the under 65 age bracket)³, and so you’d think that it would all work out just fine. However, there are more “unmarriageable” men than there are “unmarriageable” women, which skews the demographics of decent people under 65 in the other direction – there are more decent women than decent men.

Let me explain. 

Men are much more likely⁴ to commit violent crimes than are women. If you assume that few people would want to marry a violent criminal, this takes many more men out of the running, so to speak, than it does women. 

If we assume that not many people would want to marry someone with an abnormally low IQ, this takes more men than women out of the running, too. More men than women have genius-level IQs (seven out of every eight people who score in the top 1% on IQ tests are men), but there are also more men than women who have idiot-level IQs^5,6. The mean intelligence is the same or nearly so, but the distribution (or you could say, standard deviation) is wider for men than for women.

All this is to say that if you took all the decent men and all the decent women (mind you, in this case I’m using decent to mean marriageable – for the purposes of this post that means someone who is not a violent criminal and does not have a very low IQ – without any of the moral implications that the word decent often has) and paired them off, you would be left with extra women who, in a strictly monogamous society, would likely be doomed to spinsterhood and childlessness, thereby forever depriving the human race of the children they could have had, or else go and marry a low-quality man. They may feel forced into such a marriage for the sake of having children, but issues can (and often do) arise with the children of low-quality men, leaving us to conclude that this is also not ideal.

Additionally, from a primitive, biological standpoint, there are likely to end up being  fewer men left than women due to conflicts. For the entire history of humanity, with a very few exceptions, men have been the warriors. This makes a lot of sense, as the average man is stronger, faster, and better mentally suited (more aggressive and better able to compartmentalize things) for war than the average woman. This works out just fine, as the women in a primitive situation would spend much of their time in a less-than ideal situation for soldiering due to pregnancy, breastfeeding, and/or needing to care for young children. However, this means that in conflicts (which have been around as long as we have), more men end up dying than women do. This can have significant, even drastic impacts on the overall ratio of men to women, such as in the Soviet Union after WWII, when there were only 4 men per 5 women⁷. (In Soviet Russia, proper, it was even more dramatic, with 3 men per 4 women⁸.)

The solution from a biological perspective? Allow some of the decent men to marry multiple decent women, enough to take care of the surplus of women and simultaneously maximize the genetic potential (and number of children) of the group as a whole.

This surplus of decent women is one of the reasons that polyandry (the practice of one woman having multiple husbands) is a biologically unjustifiable practice, in my opinion. There is already a relative shortage of decent men. Why exacerbate the problem by allowing one woman to hog limited resources when one man would work just as well, biologically speaking?

Another reason polyandry is biologically unjustifiable is the uncertain paternity of the children. A woman has the advantage of being able to be completely and utterly certain beyond a shadow of a doubt that a child she thinks is hers truly is. A man has no such privilege. He may be intellectually sure that a child is his, but there is no biological surety he can have. (Obviously now there are genetic tests that can determine paternity, but historically – and biologically speaking – that has not been the case.)  People naturally want to take care of their own children. In a polyandrous relationship, on the surface it seems wonderful. The children can have a mother figure and multiple father figures. There’s much talk about how the lack of a father figure leads to all sorts of ills, so surely having multiple would be even better, right?

Except it doesn’t quite work like that. In polyandry, none of the men is sure that the child is his, (although there could be exceptions to this, such in the case of the male partners in the polyandrous relationship being different races) and so none of them fully act like a father. It is similar to the bystander effect⁹, which is when people are more likely not to act in an emergency (call 911, help someone who is struggling) if there are other people present, because they assume the other people will instead. Instead of the child of polyandry having multiple strong father figures, they are likely to wind up having none. An additional downside is that having multiple stepfathers is dangerous for children.  Studies have shown that stepfathers are many times more likely to assault¹⁰, abuse¹¹, and even kill¹² their stepchildren than biological fathers are. This is called the “Cinderella effect¹³”.  Although there does not seem to be much research on the “Cinderella effect” specifically in the context of polyandry, I think that it is likely present to at least some extent.

In contrast, in a polygynous marriage, the parents of each child are clear. Each child has one committed, invested father and one committed, invested mother, and additional mother figures who are not primarily responsible for the child but are still interested in their success.

The biological imperative for polygyny shows up in other places as well. A study done by the dating app OkCupid shows that women on their site rate 80% of men on their site as being below average in attractiveness¹³. Obviously that data could be skewed, but it is still reflective of the fact that women, as a whole, are choosier than men are when it comes to selecting a partner. (For comparison, in the same study, men rate 50% of women as below average and 50% of women as above average in attractiveness – exactly what you would expect.)

From a biological perspective, this makes sense. If a woman is going to invest 9 months of pregnancy and (in a primitive setting) at least a year of breastfeeding into one of her children, she’s naturally going to want to be choosy as to who the father is. In a primitive setting, she would want or need the protection of a strong, capable man while she is especially vulnerable during pregnancy and postpartum, and she doesn’t want to (nor does it make sense to) spend that much of her life on the offspring of a loser. Her best chance at long-term genetic success is to have children with a beautiful, strong, intelligent man so they (her children) will be beautiful, strong, and intelligent as well, thereby maximizing their chances for genetic success and so forth.

Hence women want the top 20% of men, and if polygyny is allowed, every woman can have a man in the top 20%, rather than settling for someone inferior. Biologically, 20 men to every 100 women is a workable number if polygamy is allowed, and this promotes many high-quality children, the biological goal for all species. The strongest, most capable men get the most breeding rights. They have strong children, and the species as a whole prospers.

To sum up: the biological goal of any species (divorced from any morality or ethics) is to reproduce as prolifically and successfully as possible, with a maximal number of strong, healthy children. In order to do this, you need to maximize the number of female members of that species who are  having children, as they are the gatekeepers for the total number of children in any given generation. In a society where only monogamy is allowed, there end up being extra females who cannot have children due to the lack of a mate. The natural solution is to allow at least some polygyny so that the species does not shortchange itself in the coming generation.

And that is the biological case for polygyny.