In a study, the researchers found adult males’ testosterone levels dropped when they were interacting with a close friend’s marital partner.
“Although men have many chances to pursue a friend’s mate, propositions for adultery are relatively rare on a per opportunity basis,” Mark Flinn, professor of anthropology in the College of Arts and Science, said.
“Men’s testosterone levels generally increase when they are interacting with a potential sexual partner or an enemy’s mate.
“However, our findings suggest that men’s minds have evolved to foster a situation where the stable pair bonds of friends are respected,” he said.
According to Flinn, evolutionarily, men who were constantly betraying their friends’ trust and endangering the stability of families may have caused a survival disadvantage for their entire communities.
The study has been published in the journal Human Nature.