Men may be biologically designed to avoid adultery with their friends' wives, new research has found.
University of Missouri researchers found men may have a natural aversion to amorous attractions to the wife next door.
The study found that adult males' testosterone levels dropped when they were interacting with the marital partner of a close friend.
Understanding the biological mechanisms that keep men from constantly competing for each others' wives may shed light on how people manage to cooperate on the levels of neighbourhoods, cities and even globally.
"Although men have many chances to pursue a friend's mate, propositions for adultery are relatively rare on a per opportunity basis," said Mark Flinn, professor of anthropology in the College of Arts and Science.
"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," Flinn said.
"Ultimately, our findings about testosterone levels illuminate how people have evolved to form alliances," said Flinn.
"Using that biological understanding of human nature, we can look for ways to solve global problems. The same physiological mechanisms that allow villages of families to coexist and cooperate can also allow groups like NATO and the UN to coordinate efforts to solve common problems," he said.
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, according to Flinn.
A community of men who didn't trust each other would be brittle and vulnerable to attack and conquest. The costs of an untrustworthy reputation would have outweighed the benefits of having extra offspring with a friend's conjugal companion.
The study was published in the journal Human Nature.
Co-authors included Davide Ponzi of MU's Division of Biological Sciences in the College of Arts and Science and Michael Muehlenbein of Indiana University.
