When you think of sexually transmitted infections, marriage is not the first thing that usually (hopefully!) springs to mind.
A study has found evidence prehistoric humans may have been encouraged into the social norm of monogamy - over polygamy - because of the spread of STIs.
But a study by the University of Waterloo in Canada, published in Nature Communications, has found evidence that prehistoric humans may have been encouraged into the social norm of monogamy - over polygamy - because of the spread of STIs.
Men having multiple sexual partners had been the norm in hunter-gathering communities, so there was a greater chance they would create offspring. However, just like today, with unprotected sex comes the increased risk of infections that can lead to infertility if not treated, such as chlamydia, syphilis and gonorrhea.
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The study found that in small societies where there was a maximum of 30 sexually mature individuals, STI outbreaks were "short-lived" and did not have a huge impact on recreating.
As agriculture grew so did society sizes and there was more opportunity for sex with an increased number of people. Without modern day treatments there were higher rates of STIs. This led to a change in mating behaviour in larger groups, with societies adapting to what was more beneficial to creating a wide pool of offspring, aka finding 'The One'.
The study also claims men who did not comply with monogamy were punished by other males, but it did not specify what those punishments were.
"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," said Chris Bauch, a professor of applied mathematics and a university research chair at Waterloo. "Our research illustrates how mathematical models are not only used to predict the future, but also to understand the past."
"Our social norms did not develop in complete isolation from what was happening in our natural environment. On the contrary, we can't understand social norms without understanding their origins in our natural environment," Professor Bauch said. "Our social norms were shaped by our natural environment. In turn, the environment is shaped by our social norms, as we are increasingly recognising."
The researchers noted that STIs may have been one factor, but also acknowledged female choice, pathogen stress and technological impacts, could have influenced monogamy over polygamy.