A whiff of tears reduces male aggression, says study
Issam AHMED
Thu, 21 December 2023
A visitor poses for photographs next to art sculptures, part of an exhibition titled "Everybody Cries Sometimes" by Thai artist Molly in Bangkok
(MANAN VATSYAYANA)
Watching someone cry often evokes an emotional response -- but according to a new study published Thursday, human tears themselves contain a chemical signal that reduces brain activity linked to aggression.
The research was carried out by the Weizmann Institute of Science, Israel, and appeared in PLOS Biology, a US science journal. Though it involved female tears, because women made themselves available as donors, it probably isn't a sex-dependent effect, the authors say.
Numerous studies have shown rodent tears contain chemicals serving as social signals they emit on demand -- female mice tears for example reduce fighting among males; and subordinate male mole rats smear themselves in their own tears so that dominant males attack them less.
To find out whether similar effects occurred in humans, a team led by PhD student Shani Agron first exposed 25 male volunteers to either "emotional" tears, or to saline. The volunteers couldn't tell what they were sniffing as both substances are clear and odorless.
The tears were obtained from six female volunteers who watched sad films in isolation and used a mirror to capture the liquid in a vial as it trickled down their cheeks.
"When we looked for volunteers who could donate tears, we found mostly women, because for them it's much more socially acceptable to cry," said Agron in a statement.
She added that since prior research had shown tears reduce testosterone levels in men, and that lowering testosterone has a greater effect on aggression in men than in women, "we began by studying the impact of tears on men because this gave us higher chances of seeing an effect."
They had the volunteers play a computer game that had been well established in prior aggression studies, and involves accumulating money while a fictitious opponent could steal their earnings.
Given the opportunity, the men could get revenge on the other player by causing them to lose money, even though in their own case they would not gain from the opponent's loss.
Such revenge-seeking, aggressive behavior in the game dropped 43.7 percent after men sniffed the tears.
This appeared to mirror what had been observed in rodents, but unlike rodents, humans don't have a structure in their noses called a vomeronasal organ, which was lost during our species' evolution and detects odorless chemical signals.
To find out what was going on, the researchers applied the tears to 62 olfactory receptors in a lab dish and found that four receptors were activated by tears, but not saline.
Finally, the scientists repeated the experiments with the men's brains connected to MRI scanners.
The imaging revealed the prefrontal cortex and anterior insula, which are related to aggression, became more active when men were provoked during the game, but the effect was not as strong if they had sniffed tears.
"We note that crying often occurs in very close-range interactions, to the extent that 'kissing teary cheeks' is a recurring theme across cultures," wrote the authors, adding that emitting chemical signals to prevent aggression was probably even more important among infants, where verbal communication isn't possible.
Smelling women's tears reduces aggression in men
Sarah Knapton
Thu, 21 December 2023
After men sniffed women’s emotional tears, their revenge-seeking aggression dropped by nearly half
Watching someone cry often evokes an emotional response -- but according to a new study published Thursday, human tears themselves contain a chemical signal that reduces brain activity linked to aggression.
The research was carried out by the Weizmann Institute of Science, Israel, and appeared in PLOS Biology, a US science journal. Though it involved female tears, because women made themselves available as donors, it probably isn't a sex-dependent effect, the authors say.
Numerous studies have shown rodent tears contain chemicals serving as social signals they emit on demand -- female mice tears for example reduce fighting among males; and subordinate male mole rats smear themselves in their own tears so that dominant males attack them less.
To find out whether similar effects occurred in humans, a team led by PhD student Shani Agron first exposed 25 male volunteers to either "emotional" tears, or to saline. The volunteers couldn't tell what they were sniffing as both substances are clear and odorless.
The tears were obtained from six female volunteers who watched sad films in isolation and used a mirror to capture the liquid in a vial as it trickled down their cheeks.
"When we looked for volunteers who could donate tears, we found mostly women, because for them it's much more socially acceptable to cry," said Agron in a statement.
She added that since prior research had shown tears reduce testosterone levels in men, and that lowering testosterone has a greater effect on aggression in men than in women, "we began by studying the impact of tears on men because this gave us higher chances of seeing an effect."
They had the volunteers play a computer game that had been well established in prior aggression studies, and involves accumulating money while a fictitious opponent could steal their earnings.
Given the opportunity, the men could get revenge on the other player by causing them to lose money, even though in their own case they would not gain from the opponent's loss.
Such revenge-seeking, aggressive behavior in the game dropped 43.7 percent after men sniffed the tears.
This appeared to mirror what had been observed in rodents, but unlike rodents, humans don't have a structure in their noses called a vomeronasal organ, which was lost during our species' evolution and detects odorless chemical signals.
To find out what was going on, the researchers applied the tears to 62 olfactory receptors in a lab dish and found that four receptors were activated by tears, but not saline.
Finally, the scientists repeated the experiments with the men's brains connected to MRI scanners.
The imaging revealed the prefrontal cortex and anterior insula, which are related to aggression, became more active when men were provoked during the game, but the effect was not as strong if they had sniffed tears.
"We note that crying often occurs in very close-range interactions, to the extent that 'kissing teary cheeks' is a recurring theme across cultures," wrote the authors, adding that emitting chemical signals to prevent aggression was probably even more important among infants, where verbal communication isn't possible.
Smelling women's tears reduces aggression in men
Sarah Knapton
Thu, 21 December 2023
After men sniffed women’s emotional tears, their revenge-seeking aggression dropped by nearly half
- Tetra Images
Smelling women’s tears reduces male aggression, scientists have found, in a breakthrough that may help solve the mystery of why humans cry.
Humans and dogs are the only animals that shed tears when overcome with emotion, but scientists such as Charles Darwin believed the release served no useful function.
Now researchers at the Weizmann Institute of Science in Israel have found that tears contain social signals which appear to act as a ‘chemical blanket’ to protect the weeper.
Smelling women’s tears reduces male aggression, scientists have found, in a breakthrough that may help solve the mystery of why humans cry.
Humans and dogs are the only animals that shed tears when overcome with emotion, but scientists such as Charles Darwin believed the release served no useful function.
Now researchers at the Weizmann Institute of Science in Israel have found that tears contain social signals which appear to act as a ‘chemical blanket’ to protect the weeper.
Sniffing for answers
In a series of experiments, men were exposed to either women’s emotional tears or saline, without knowing what they were sniffing nor being able to distinguish between the two, since both are odourless.
Next they were asked to play a game designed to trigger revenge-seeking aggressive behaviour in one player towards another.
The team found that after the men sniffed women’s emotional tears, their revenge-seeking aggression during the game dropped by nearly half - 44 per cent.
Brain scans during the experiments also showed that regions related to aggression were less active while the men were sniffing tears.
And when researchers applied the tears to 62 human olfactory - smell - receptors in a laboratory dish, they found that some were activated.
Tears form ‘chemical blanket’
Professor Noam Sobel, of Weizmann’s Brain Sciences Department, said: “We’ve shown that tears activate olfactory receptors and that they alter aggression-related brain circuits, significantly reducing aggressive behaviour.
“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.”
All land mammals have tear glands in their eyes, but in most other animals it was thought they were only used to keep eyes moist and clean.
Recent studies, however, have shown that tears of female mice contain chemicals that affect aggression networks in the brain of male mice, reducing fighting. Subordinate males of blind mole rats will also smear themselves in tears to reduce a dominant male’s aggressive behaviour towards them.
It was recently also discovered that dogs shed emotional tears, although it is not yet known whether the chemical signals have evolved to be picked up by other dogs or humans.
Reduced testerone
Prof Sobel’s team also previously showed that sniffing women’s emotional tears reduced testosterone levels in men, resulting in diminished levels of sexual arousal.
Doctoral student Shani Agron, of Sobel’s lab, said: “We knew that sniffing tears lowers testosterone, and that lowering testosterone has a greater effect on aggression in men than in women, so we began by studying the impact of tears on men because this gave us higher chances of seeing an effect.
“Now, however, we must extend this research to include women, to obtain a fuller picture of this impact.”
The team believes that the study may also help explain why babies cry so much.
“Infants can’t talk, so for them relying on chemical signals to protect themselves against aggression can be critical,” added Agron.
The research was published in the journal PLOS Biology.
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