Sniffing women’s emotional tears made men behave less aggressively in a provocation game, cutting their revenge-taking by 43.7%, a study in PLOS Biology found.
Shani Agron, Noam Sobel and colleagues at the Weizmann Institute of Science in Israel, working with Claire A. de March and Hiroaki Matsunami of Duke University Medical Center, published “A chemical signal in human female tears lowers aggression in males” on December 21, 2023.
Tears versus saline
Rodent tears carry chemical signals that block male aggression. Earlier work had shown that human tears contain an odorless signal that lowers testosterone in men, but what that does to behavior was unclear.
Six women donated emotional tears. As a control, the team trickled saline down the same donors’ cheeks and collected it the same way. Participants could not tell the two apart: they did not differ in rated pleasantness, intensity or familiarity.
Twenty-five men, retained from 31 recruited, came to the lab on two consecutive days, sniffing tears on one day and saline on the other, in double-blind, counterbalanced order. A pad carrying the stimulus stayed on their upper lip throughout.
They then played a standard aggression task in which an opponent, in fact a computer, “unfairly” took money from them, and they could take revenge by deducting money at no gain to themselves.
The ratio of revenge responses to provocations averaged 1.67 after saline and 0.94 after tears, a 43.7% reduction in aggression.
Receptors and brain networks
In cell experiments, the researchers applied tears to 62 human olfactory receptors and identified four, OR2AG2, OR11H6, OR5A1 and OR2J2, that responded in a dose-dependent manner.
Repeating the game during brain imaging with 24 men, they found that sniffing tears increased functional connectivity between brain areas involved in smell and aggression, while lowering overall activity in the aggression network, including the left anterior insula and prefrontal cortex.
The authors point to limits. Humans have about 350 receptor types and only 62 were tested, and a receptor that responds is not proof it causes the effect. Women were not tested as sniffers, partly because the study already required more than 160 ml of tears from at least 125 donation sessions.
They speculate that all tears may carry such a signal, which could matter most for infants, who cannot use words to curb aggression against them.
Study Details:
- Title: A chemical signal in human female tears lowers aggression in males
- Authors: Shani Agron, Claire A. de March, Reut Weissgross, Eva Mishor, Lior Gorodisky, Tali Weiss, Edna Furman-Haran, Hiroaki Matsunami, Noam Sobel
- Journal: PLOS Biology
- Publication Date: December 21, 2023
- DOI: 10.1371/journal.pbio.3002442