Our ancestors didn't choose monogamy out of anything so high-minded as love or religion, according to a new study published Tuesday. Rather, it was most likely due to skyrocketing rates of chlamydia, syphilis, and gonorrhea from all the polygamous sex being had.

Within hunter-gatherer groups of 30 or fewer people, STI outbreaks would have a minimal effect on the larger population and be over relatively quickly, Tech Times reports.

But as humans took up farming and settled in larger groups, infertility-causing STIs would spread rapidly and hurt a group's ability to propagate itself, according to AFP.

Researchers were able to demonstrate this using computer modeling. "This research shows how events in natural systems ... can strongly influence the development of social norms," researcher Chris Bauch says in a press release.

According to researchers, men with multiple female partners would have greater rates of STIs and less chance of reproducing. As monogamous men bore more children, their behavior was copied.

It would also benefit monogamous men to punish non-monogamous men in order to secure the future of the group. The study could help explain the mystery of why multiple groups of ancient humans turned to monogamy despite its rarity in the natural world and difficulty in implementing.

So, if science cures STIs, will we see a return to our swinging ways? "Modern societies are more complicated," Bauch tells AFP. "I think it is premature to speculate that marriage will disappear, or that polygyny will return." (This study shows raising taxes on booze can reduce STI rates.)

This article originally appeared on Newser: Study: STDs, Not Love, Are Why Humans Became Monogamous

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