Originally posted on Feb 21, 2024 on our Patreon.
To understand if humans are naturally polygamous or monogamous, we must consider important social and biological processes. I intend to respect both sides of this controversial topic, while giving my best explanation of evolutionary and cultural facts as we know them.
Cultural:
Most (82%) human societies allow or practice cultural polygamy to some degree. However, even within these societies, the vast number of members will be monogamous. In traditional settings, the ability to have multiple wives is generally only financially possible for the wealthy. In these countries where some men have many wives and some have none, appear to face statistically greater amounts of political instability and conflict.
In countries in the United States and Europe, which tend towards an Abrahamic religious view, the act of marrying more than one partner is illegal. However, humans are hardly a “true lifemating species,” which only settles with one partner over the course of a lifetime. It’s very common for a person to engage in casual dating or experience multiple dedicated partners. Some argue that this is “serial monogamy,” while others argue that it’s definitionally polyamorous.
However, certain cultures also experience advantages in being polyamorous. For example, in traditional Tibetan polyandry, one woman would take on multiple husbands. These were often a set of related brothers, who would all act as fathers to her children. Living in such a cold and environmentally extreme location, this practice kept families protected closely together, provided agricultural labor, and increased reproductive success. As such, there is evidence that polyamorous practices can be successful family strategies.
Biological:
Sexual dimorphism is when one sex of a species has specific traits. This is most commonly associated with size. In primates, in sexually dimorphic species, the males are larger than the females. Species that are highly sexually dimorphic are more likely to be polygamous, and ones with low sexual dimorphism are highly associated with monogamy.
Humans are slightly more sexually dimorphic than gibbons, which are a true monogamous mating species. That is, they only pair with one individual for life. However, humans are still less sexually dimorphic than chimpanzees. These primates are polygamous but show a much stronger preference for mates they have an emotional bond and daily relationship with. This theory would suggest that humans fair on the spectrum between these two points.
Another form of sexual dimorphism is canine size. Primates with large canines tend to be naturally selected from species where male intrasexual violence occurs over mates. However, as we see in humans, there is no sexual dimorphism in canine size, and people do not have the visibly apparent canines that primates generally do. This suggests that human males are likely not physically competing for mates.
In primates, larger testicle size and higher sperm output are associated with mate competition. This can perhaps best be seen in the polyamorous chimpanzees. Because the females may mate with multiple males, sperm competition is prized to ensure parentage. Chimpanzees developed testicles as large as human palms, with a large gamete output. In comparison, homo sapiens testicles are small, and differences in size show no correlation to sperm output. This suggests that human females are less likely to have sex with multiple males concurrently.
In primates, there is a distinction between those who show when they are reproductively fertile through swellings, and those who go through invisible estrus. One notable species of the later type are the gorillas. By not displaying when they are in heat, female gorillas secure male protection year-around and choose when they desire to initiate mating. Although this shouldn’t be taken as a 1:1 similarity to humans, it is a notable connection of behavior and anatomy.
Compared to non-human animals and primates, humans have notably low non-paternity rates. That is, describing when males are raising offspring other than their own. (For humans, we exclude intentional adoption from these statistics). That is to say, research has shown that human males are the father of offspring they perceive to be theirs 90% of the time.
Analysis:
Without omitting evidence, it is impossible to deny that humans have a tendency, biologically and culturally, towards monogamy. However, there are also examples of individuals and cultures who prefer to be polygamous all on their own will and desire. In these cases, the greatest reasonings appeal to human bond, beliefs on respect and autonomy, and access to resources. As such, there are situations wherein being monogamous or polyamorous each have their own merits and benefits.
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What do you think of this analysis?
Did I miss a crucial culture or feature?