Introduction
When someone starts to cry, others often feel empathy and concern. But the biological reasons for shedding tears can go beyond simply evoking pity. It seems that the tears themselves play a role as a chemical mediator for peace between men and women, a fact that new research has discovered.
The Effect of Tears on Aggression
According to results published in the journal PLOS Biology, women’s tears reduce aggression in men who are close enough to smell them, a finding confirmed through human behavioral studies, brain imaging, and molecular biology. Researchers believe that tears from non-women may have a similar effect, but this has not yet been tested.
The Role of Tears in Reducing Aggression
The new study suggests that the underlying reason for women shedding emotional tears is “to convey a chemical signal that reduces aggression,” according to Shani Agron, the co-author of the study. She believes this mechanism is common among many mammals.
The Effect of Tears on Human Behavior
The production of tears has long been considered a unique behavior of humans, but this is a misconception. For example, dogs shed tears when they are reunited with their owners after a period of separation. The tears of baby mice contain molecular signals that cause female mice to reject male advances, while encouraging female mice to cease mutual fighting and mate with males instead. Additionally, some mice go so far as to cover themselves with their own tears to redirect aggression away from dominant members of their group.
The Effect of Tears on Human Behavior
Like other mammals, humans communicate information through body odors. However, it has not been clear whether tears would have any olfactory effect on human behavior since people cannot detect their scent. Furthermore, while most mammals have a secondary sensory organ responsible for detecting pheromones, it is believed that this organ in humans is a vestige.
The Effect of Tears on Human Behavior
Evidence that tears can chemically influence human behavior first emerged in 2011, when Sobel and colleagues published a study in the journal Science showing that women’s tears lower testosterone levels and reported sexual arousal in men. It took years of effort to conduct a more detailed follow-up, partly due to the difficulty of collecting tears from donors. Researchers need at least one milliliter of tears to use for each experimental participant, which is “a large amount of tears,” according to Sobel. Additionally, onions or other irritants cannot be used to make someone’s eyes water, as “these are a completely different type of tears,” adds Agron.
The Effect of Tears on Human Behavior
To collect the tears used in the new study, the team reached out to volunteers who cry easily. Only a few men showed up, and none of them could produce enough tears to qualify. Among about 100 women who volunteered, only six were able to provide enough tears for collection. Participants could use any means they wished to summon tears, from listening to sad music to reading an emotional letter, but most relied on the “sad movie library” in the lab, according to Agron. In addition to the tears, researchers also collected drops of saline that were dripped on the faces of the women for use in control experiments.
The Effect of Tears on Human Behavior
Researchers gathered data from 25 male volunteers who played a game in the lab designed for aggression studies. During the competitive game, participants were led to believe that their opponent was another person. However, it was actually a computer algorithm. Sometimes, the opponent stole money from participants, who could then either choose to retaliate, without gaining any financial rewards for themselves, or allow their opponent to escape while continuing to collect more money for themselves. According to the researchers, aggression was calculated by the number of times a participant chose to retaliate divided by the number of times they were provoked. The team also repeated this experiment with a second group of 26 male volunteers who played the game while inside an MRI scanner, allowing for the collection of brain activity data.
The Effect
Tears on Human Behavior
All participants played the game twice, and before each session, they were asked to sniff from a “scent jar” that they were told contained “various scents,” but which actually contained either tears or saline solution. Researchers found that when men inhaled women’s tears, they were approximately 44 percent less aggressive in the game compared to when they inhaled saline solution. The reduction in aggressive behavior was also accompanied by changes in neural activity. Researchers noted that men’s brains after inhaling tears showed reduced activity in the prefrontal cortex and left anterior part, which are areas associated with aggression and decision-making. Connectivity between the left anterior part and the amygdala, the region responsible for processing emotions and part of the olfactory network, also increased.
The Effect of Tears on Human Behavior
The team worked with colleagues at Duke University to test the effect of tears and saline solution on 62 human computer receptors in the lab. Four receptors were found to respond to tears and not to the saline solution. This discovery helps answer a “big question” about how humans process scent-like signals, according to Agron.
Future Research
Agron, Sobel, and their colleagues are now interested in conducting future experiments to test the effects of women’s tears on other women and the effects of children’s tears on adults. Sobel hypothesizes that children’s tears, in particular, will have a calming effect on adults. “Children can’t communicate with you verbally,” he says. “But evolution may have given children this tool to reduce aggression.”
Conclusion
The fact that humans continue to produce tears throughout adulthood suggests, according to Agron, that crying is likely a “behavior that serves us throughout life.”
Source: https://www.scientificamerican.com/article/sniffing-womens-tears-makes-men-less-aggressive/
Source: https://www.scientificamerican.com/article/sniffing-womens-tears-makes-men-less-aggressive/
Leave a Reply