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Chemical in female tears lowers male aggression, study finds

The scientists behind the study suggest that the chemical reaction evolved as a way to protect infants

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France’s Antoine Griezmann carries his crying daughter after his team won the final match between France and Croatia at the 2018 soccer World Cup, Sunday, July 15, 2018.

France’s Antoine Griezmann carries his crying daughter after his team won the final match between France and Croatia at the 2018 soccer World Cup in the Luzhniki Stadium in Moscow, Russia, Sunday, July 15, 2018.

Martin Meissner, Associated Press

A study published in the scientific journal Plos Biology suggests that female tears contain a chemical that reduces male aggression.

Noam Sobel, co-author of the study and neurobiologist at the Weizmann Institute of Science, said in a statement, “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.”

Humans aren’t the only ones who cry

As Sobel noted, the study is similar to recent studies on the ways rodents use tears. One study observed blind male mole rats covering themselves in their own tears to reduce aggression from dominant male mole rats. Another study found that chemicals in female mice tears affect the area of male mice’s brains that control aggression, lessening it.

Scientific American recently referenced a study exploring how dogs secrete tears when reunited with their owners after extended periods of time. The study explained that tear secretion in dogs “is mediated by oxytocin, and that tears in dogs’ eyes could facilitate human caregiving behavior.”

How was this study conducted?

Over 100 women volunteered to produce tears for the Plos Biology study, but only six were able to provide at least one milliliter, which Sobel described as “a lot of tears,” per Scientific American. Most of the participants watched sad movies to provoke emotional tears.

To test the effects of the tears, scientists worked with male participants who were divided into two groups. Both groups were asked to play a video game against an opponent they were told was human but which was actually a bot. While playing, the bot would “unfairly” take game money from the participant and sabotage him for seemingly no reason.

The first group’s aggressiveness was measured by dividing the number of times they took revenge on the bot by the times they were provoked. The second group’s aggressiveness was measured by an MRI scanner, analyzing brain activity.

Each male participant played the rigged video game twice, and they were periodically asked to sniff what they were told was “assorted odors.” The assorted odors were really just separate vials of saline solution and tears from the female participants.

Female tears ‘significantly’ reduced male aggression

Compared to the saline solution the participants sniffed, female tears reduced aggression by roughly 44%. The tears also had “a dampening affect” on several areas of the brain, researchers found. They concluded that female emotional tears had a “significant” influence on decreasing male aggression.

Sable told The Guardian he believes the aggression-reducing chemicals in tears developed to protect infants from harm.

He explained, “Babies can’t say: ‘Stop being aggressive towards me’. They are very limited in their ability to communicate, and they are helpless as well. They have a vested interest in lowering aggression and that reflects the sad reality of aggression towards babies.”

A professor of emotions and well-being at the University of Tilburg in the Netherlands told The Guardian, “It makes sense if tears in some way inhibit aggression because it’s common knowledge that infants that cry a lot are at risk for physical abuse. It might help them to survive.”