Human tears contain a chemical signal that blocks aggression in men, a study has found.
They got a group of men to smell either women’s emotional tears or saline – a mixture of salt and water – while they played a two-person game.
The game was designed to elicit aggressive behavior against the other player, whom the men were led to believe was cheating.
When given the opportunity, the men could get revenge on the other player by causing them to lose money.
Revenge-seeking aggressive behavior during the game dropped by more than 40 percent after the men sniffed women’s emotional tears.
Human tears contain a chemical signal that blocks aggression in men, a study has found (stock image)
When repeated in an MRI scanner, imaging showed two regions of the brain associated with aggression – the prefrontal cortex and anterior insula – became more active when the men were provoked during the game, but did not become as active in the same situations when the men were sniffing the tears.
The study helps address the long-standing mystery of why we cry, the researchers say.
Charles Darwin was puzzled by emotional crying, which appeared to have no useful function beyond the role that tears play in lubricating the eye – so he concluded that crying must have evolved in humans by chance.
Since then, however, studies have shown that the tears of certain mammals – mainly rodents – contain chemicals serving as social signals that can be emitted on demand.
Aggression in male rodents has found to be blocked when they smell female tears, while subordinate blind mole rat males smear themselves in tears to reduce a dominant male’s aggressive behavior toward them.
Writing in the journal Plos Biology, the team from the Weizmann Institute of Science in Israel said: ‘We found that just like in mice, human tears contain a chemical signal that blocks conspecific male aggression.
‘This goes against the notion that emotional tears are uniquely human.’
Researcher Shani Agron said the effect is likely to be most important when verbal communication is impossible – for example, in interactions with babies.
‘Infants can’t talk, so for them replying on chemical signals to protect themselves against aggression can be critical’, she said.
The team said their future research will explore whether the study’s findings also apply to women.
Professor Noam Sobel, who oversaw the research, said; ‘We’ve shown that tears activate olfactory receptors and that they alter aggression-related brain circuits, significantly reducing aggressive behavior.
‘These findings suggest that tears are a chemical blanket offering protection against aggression – and that this effect is common to rodents and humans, and perhaps to other mammals as well.’
Back in 2011, Professor Sobel’s team showed that sniffing women’s emotional tears reduced testosterone levels in men, resulting in somewhat diminished levels of sexual arousal.
Recent studies have found that dogs also shed emotional tears.
However, more research is needed to determine whether these tears contain chemical signals that can be picked up by other dogs or by humans.
Experts from Duke University School of Medicine were also involved in the study.
This post first appeared on Dailymail.co.uk
