We May Have Evolved to Have Sex in Private to Stop Others Stealing Our Mate, Study Says

People may have sex in private because they want to prevent others from becoming turned on and attempting to steal their partner, according to a study.

Author Yitzchak Ben Mocha, who was based at four institutions for the study including Germany's Max Planck Institute for Ornithology, conducted the study in two parts. First, he reviewed more 4,572 accounts of different cultures, known as ethnographies, to analyze the sexual norms of 249 cultures across 35 geographical regions.

Ben Mocha told Newsweek via email he was only interested in "socially legitimate sexual intercourse," such as that between married partners, and not types that go against norms. He gave the example of incest where people may conceal it to avoid punishment. Public sex acts, which may be part of certain festivals, were also excluded.

Next, he drew on existing studies on the sexual behavior of animals, including evolutionary theories on this topic.

In findings in the journal Proceedings of the Royal Society B, Ben Mocha showed that although people's living conditions may mean they can't always find privacy when having sex, individuals from "virtually all cultures" took steps to hide.

Ben Mocha told Newsweek he was inspired to carry out the study after he noticed that dominant members of the Arabian babblers bird society hide themselves while they mate, even though they don't risk being attacked by subordinate members of their group.

At the end of his study, Ben Mocha found hiding during sex present only in two species: humans and the Arabian babblers. Based on his work, Ben Mocha suggested that people, and Arabian babblers, have evolved to seek privacy partly to control who can sees their partner in a sexual light. In turn, this may enable them to control who their partner mates with, and prevent others from trying to mate with them.

The study also sheds light on the cognitive abilities and evolution needed to hide sex from others, Ben Mocha told Newsweek. It helps us to understand what behaviours and thinking skills individuals in a group may develop in order to balance their need to be a co-operative member of the team while being competitive.

However, Ben Mocha said conclusions made using ethnographies to analyze sexual norms "should be viewed cautiously," as people may behave differently in these circumstances. For instance, they may not have sex in the presence of anthropologists who come from cultures where public sex is frowned upon. Interviewees are often reluctant to discuss their sex lives with ethnographers, Ben Mocha said, so these behaviors are poorly documented.

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A stock image shows a couple in bed. A researcher has investigated why most people prefer to have sex in private. Getty