Humans may only be monogamous due to sexually transmitted infections. Scientists found that prehistoric humans may have developed social norms that favor monogamy due to the presence of STIs and peer pressure.
In early hunter-gatherer populations, it was actually common for a few males to monopolize mating with multiple females. This increased their number of offspring. In these small societies, where there was a maximum of 30 sexually mature individuals though, STI outbreaks were short-lived and didn't have a significant effect on the population.
With that said, societies grew over time, especially with the advent of agriculture. Researchers found that when population grows, the presence of STIs decreases fertility rates more among males with multiple partners. This, in turn, changes which mating behavior proves to be most beneficial to individuals and groups.
"Our social norms did not develop in complete isolation from what was happening in our natural environment," said Chris Bauch, one of the researchers at the University of Waterloo in Canada. "On the contrary, we can't understand social norms without understanding their origins in our natural environment. Our social norms were shaped by our natural environment. In turn, the environment is shaped by our social norms, as we are increasingly recognizing."
With that said, STIs may just be one factor among many, including female choice, pathogen stress and technological impacts. However, it certainly is a likely cause of the alteration of human behavior from polygamy to monogamy.
"This research shows how events in natural systems, such as the spread of contagious diseases, can strongly influence the development of social norms and, in particular, our group-oriented judgments," Bauch said. "Our research illustrates how mathematical models are not only used to predict the future, but also to understand the past."
The findings show how it may be possible that humans started out as polygamous and then, eventually, their society evolved to support monogamy. With that said, it should be noted that STIs are probably not the only thing that drove societies to embrace monogamy. It's likely that rights to property and factors associated with agriculture contributed.
The findings were published in the April edition of the journal Nature Communications.
