Chemicals found in women's tears reduce aggression in men by almost 44%. The corresponding study was published in PLOS Biology.
Studies show that rodent tears contain chemosignals that block male aggression. While human tears contain a chemosignal that lowers male testosterone, it remains unclear whether it affects aggression. As reduced testosterone is linked to reduced aggression, researchers set out to investigate the effect of female human tears on male aggression.
To do so, they recruited over 60 healthy men with an average age of 26 years old. They then asked the men to inhale from a 'sniff jar' that contained either women's emotional tears or saline before playing a two-person game with a computer algorithm. Both tears and saline were odorless, and men were not told which they were sniffing.
The game was designed to incite aggressive behavior against the opponent by giving the impression they were cheating. When given an opportunity, men could seek revenge by causing them to lose money. Aggressiveness was calculated by the number of times participants chose revenge divided by how often they were provoked.
Ultimately, the researchers found that men sniffing emotional tears were 43.7% less likely than those sniffing saline to exhibit revenge-seeking aggressive behavior. They further found that sniffing women's tears reduced activity in areas of the brain linked to aggression after analyzing men playing the game while undergoing an MRI scan.
"Our results imply that like in rodents, a human tear–bound chemosignal lowers male aggression, a mechanism that likely relies on the structural and functional overlap in the brain substrates of olfaction and aggression. We suggest that tears are a mammalian-wide mechanism that provides a chemical blanket protecting against aggression," wrote the researchers.
The researchers are now interested in testing the effects of women's tears on other women, as well as babies' tears on adults. According to Scientific American, co-senior author Noam Sobel, a neurobiologist at the Weizmann Institute of Science, hypothesizes that baby tears are likely to have an aggressiveness-lowering effect on adults.
Sources: Neuroscience News, Scientific American, PLOS Biology