New research, published Dec. 21 in the open-access journal at PLOS Biology, shows that tears from women contain chemicals that block aggression in men. The study, led by Shani Agron at the Weizmann Institute of Science in Israel, finds that smelling tears leads to reduced aggression-related brain activity, which results in less aggressive behavior.
Male aggression in rodents is known to be inhibited when they smell female tears. This is an example of social chemosignaling, a process that is common in animals but less common—or less well understood—in humans. To determine whether tears have the same effect in humans, researchers exposed a group of men to either women’s emotional tears or saline while playing a two-person game. The game was designed to provoke aggressive behavior against the other player, whom the men believed was cheating. When given the chance, men could take revenge on the other player by causing them to lose money. The men did not know what they were smelling and could not distinguish between tears or saline, both of which were odorless.
Aggressive revenge behavior during play was reduced by more than 40% after men smelled women’s emotional tears. When repeated on an MRI scanner, the functional imaging showed two brain regions associated with aggression — the prefrontal cortex and the anterior insula — became more active when the men were challenged during the game, but not as much active in the same situations when men smelled tears. Individually, the greater the difference in this brain activity, the less often the player retaliated during the game. Finding this link between tears, brain activity and aggressive behavior suggests that social chemosignaling is a factor in human aggression rather than just an animal curiosity.
The authors add, “We found that just as in mice, human tears contain a chemical signal that blocks male aggression. This contradicts the notion that emotional tears are uniquely human.”