Smelling female tears was shown to dramatically reduce male aggression and lower activity in brain networks related to aggression, according to an intriguing study. It’s been proposed that the effect, which is brought on by chemical signals in tears and is observed in rodents as well, has a defensive purpose.
Emotional tears confused Charles Darwin, who believed they were only good for lubricating the eyes. Despite the belief that emotional weeping is a characteristic unique to humans, scientists have discovered that since Darwin, mammalian tears have contained chemicals that serve as social signals, one of which is to lessen aggression.
For instance, the signals found in female mice’s tears prevent intermale aggression by reducing activity in the brain networks associated with aggression in males. Additionally, to lessen the aggression of the dominant male toward them, subordinate male blind mole rats cover themselves in tears.
Recently, scientists at Israel’s Weizmann Institute of Science have carried out a number of tests to find out if sniffing human female tears can lessen male aggression in the same way that it does in rodents and what physiological effects it has on men’s brains.
“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,” stated Shani Agron, the study’s lead and co-corresponding author.
Although there is little evidence of human tear chemosignaling, some of the researchers from the current study discovered in a previous study that when men sniff women’s tears, it corresponds to physiological markers of arousal and testosterone levels.
Initially, the investigators investigated if male aggression could be decreased by smelling the tears of women. Six human donors between the ages of 22 and 25 provided “emotional” tears by watching depressing movie clips alone. A two-person money game involving 25 men and an opponent they were told was human but was actually a computer algorithm was presented to them. The purpose of the game was to make the male feel as though their opponent was cheating, so they would react aggressively against them. When the chance arose, the man could exact revenge on his rival by making them lose money while receiving no benefit himself.
The participants were not told what they were sniffing before the game began. They were asked to sniff either female tears or a saline solution, both of which have no smell. When exposed to tears, the researchers saw a 43.7% decrease in aggressiveness. They performed a bootstrap analysis, a statistical technique that resamples a single data set to produce numerous simulated samples, to assess the robustness of their findings. The analysis revealed that there was a 2.9% chance of obtaining this result by chance, indicating that the primary function of chemosignals in human emotional tears is to block aggression, just like in rodents.
Subsequently, the scientists examined the impact of sniffing tears on the subjects’ brains. A functional magnetic resonance imaging (fMRI) scan was performed on 26 male participants while they were playing the money game after being exposed to tears or saline. The researchers observed decreased activity in the left anterior insula cortex (AIC) and bilateral prefrontal cortex (PFC), two brain regions linked to aggression, after subjecting the subjects to tears. Activity in these regions was significantly correlated with the experimental condition (tears versus saline).
Examining the functional connectivity of the brain, they discovered that tears only affected the left AIC, which showed markedly enhanced connectivity with the right piriform cortex and amygdala. These areas are linked to a functional network that is involved in aggression and olfaction (smelling), in addition to having structural connectivity.
Noam Sobel, another of the study’s corresponding authors, stated that “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.”
In fact, a 2022 study discovered that dogs’ tear production considerably increased upon being reunited with their owner, but not with a known non-owner, indicating that dogs were capable of shedding happy, emotional tears. To find out if these tears contain chemosignals that humans or other dogs can pick up, more research is necessary.
The researchers are eager to carry out more research now that they have established the impact of sniffing tears on men’s behavior.
“When we looked for volunteers who could donate tears, we found mostly women because, for them, it’s much more socially acceptable to cry,” Agron stated. “Now, however, we must extend this research to include women to obtain a fuller picture of this impact.”