Do men have an evolutionary aversion to affairs with their friends wives? Adult males' testosterone levels drop when with spouses of close friends Usually testosterone levels spike in the company of potential sex partners Researchers suggest this could have been a result of evolution Untrustworthy men would have harmed social bonds of communities Men seem to have an evolutionary aversion to becoming sexually attracted to their friends' wives, research claims. A University of Missouri study that found adult males' testosterone levels dropped when they were interacting with the spouse of a close friend. Understanding the biological mechanisms that stop men constantly competing for each others' partners may shed light on how people cooperate to form communities, the research claims. Purely platonic: New research claims that men have a biological aversion to seducing their friends' wives, with their testosterone levels dropping when interacting with their buddies' conjugal companions Mark Flinn, professor of anthropology at Missouri and lead author on the study, said: 'Although men have many chances to pursue a friend's mate, propositions for adultery are relatively rare on a per opportunity basis. '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.' 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, says Professor 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. Misfits? 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 researchers say A cautionary tale of the dangers of adultery can be found in the myth of Camelot. Sir Lancelot betrayed King Arthur by seducing Guinevere. Soon after, the fellowship of the Knights of the Round Table disintegrated and the kingdom fell. The alliance of powerful males could not hold once that trust had been lost. Professor Flinn claims that his team's findings might even help us along the path to world peace and cooperation. 'Ultimately, our findings about testosterone levels illuminate how people have evolved to form alliances,' he said. 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 U.N. to coordinate efforts to solve common problems. The more we view the Earth as a single community of people, the greater our ability to solve mutual threats, such as climate change. Dr Flinn's findings were reported in the journal Human Nature. Co-authors include Davide Ponzi of Missouri's Division of Biological Sciences and Michael Muehlenbein of Indiana University.