Does stress make you itchy? You’re not alone, and you may be engaging in an elaborate conflict-prevention strategy that evolved millions of years ago.
Researchers from the University of Plymouth spent eight months in Cayo Santiago, Puerto Rico, observing a group of wild rhesus macaques, Macaca mulatta, and watching for patterns—specifically in their scratching habits.
The scientists found that the macaques were scratching the most at times of heightened social stress, such as when they had to deal with a higher-ranking or unknown monkey. This echoes research conducted on human stress: We often have the same response when forced to confront our bosses or approach strangers.
It turns out there’s a good reason for this—to avoid squabbles. In the study, higher-ranking monkeys were 25 percent less likely to get aggressive towards scratching monkeys compared with non-scratching ones.
According to Jamie Whitehouse, lead author of the study, this could mean that monkeys see scratching as a signal of stress—and attacking a stressed-out monkey may not be a very good idea. “As scratching can be a sign of social stress, potential attackers might be avoiding attacking obviously stressed individuals because such individuals could behave unpredictably or be weakened by their stress,” Whitehouse said in a release on ScienceDaily, “meaning an attack could be either risky or unnecessary.”
This is not the first time that monkeys are helping humans understand our own anxiety. A 2013 study by researchers from Manchester and Liverpool looked at the behavior of 600 Barbary macaques and found that “middle monkeys” stress out the most as they juggle aspirations to rise socially with the fear of being pushed out from the bottom of the hierarchy. That’s life in the middle-class for you.