Sexually transmitted infections, or STIs, may have been the reason why early humans eventually learned to become monogamous. A recent stud...
Sexually transmitted infections, or STIs, may have been the reason why early humans eventually learned to become monogamous.
A recent study made use of computer modeling to determine that humans shifted from polygynous societies, or those where men had several long-term partners while women were limited to one, to monogamous ones because of the advent of STIs. These infections would have affected large communities as the agricultural age started about 10,000 years ago. According to co-author Chris Bauch of the University of Waterloo in Canada, polygynous behavior was “more common” in hunter gatherers, but faded out “when we became agriculturists.”
According to Bauch and co-author Richard McElreath of the Max Planck Institute for Evolutionary Anthropology, STIs were limited to short-term outbreaks regardless whether people are monogamous or polygynous when communities are made up of 30 people or less. But when communities consist of 300 or more people, these diseases were able to linger in these larger populations, and spread faster in polygynous societies. That might have forced some agricultural societies to enforce monogamy to curb STI spread.
“It basically suggests that the hypothesis is plausible,” Bauch explained. “I think it’s really a starting point for work that can help us better understand how our social norms are a reaction to our natural environment.”
But why polygyny in those early days? Previous studies had suggested that men with multiple wives and more children tended to have more power than men who stayed monogamous and typically had less children. When agriculture began to rise, however, societies imposed laws against having multiple wives, much like most modern societies. Bauch believes that, aside from controlling STIs, these laws and agriculture in itself may have allowed more men to be healthier, and also reduced violence that would often break out in polygynous societies.
“That really illustrated why it’s not enough to have to be a monogamist – you have to be a punishing monogamist,” he said. “I was surprised at some of the complex dynamics that can emerge in this model that would be difficult to think up off the top of your head, but in the computer simulation, you can see them unfolding before your eyes.”
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