A new study published in PLOS Biology reveals that human tears have a surprising effect on men’s behavior and brain activity. According to the researchers, men who sniffed women’s tears before playing a competitive game were significantly less aggressive and had lower activity in two brain regions associated with aggression.
Tears are a common and natural response to sadness, pain, or joy. But why do we cry? What is the purpose of tears? Charles Darwin was puzzled by this phenomenon, as he saw no apparent function for tears in human evolution. He wrote in his book The Expression of the Emotions in Man and Animals: “We must look at weeping as an incidental result, as purposeless as the secretion of tears from a blow outside the eye.”
However, modern science is challenging this view. Tears are not just for eye protection or emotional relief. They are also a form of social communication, a way of sending chemical signals to others. These signals can affect the mood, behavior, and physiology of the receiver, depending on the context and the relationship between the sender and the receiver.
The Power of Women’s Tears
The researchers, led by Shani Agron at the Weizmann Institute of Science in Israel, wanted to test the effect of women’s tears on men’s aggression. They collected tears from six female volunteers who watched sad movies, and exposed 50 male participants to either tears or saline (a control substance) without telling them which one. The tears and the saline were both clear and odorless, so the men could not distinguish them by sight or smell.
The men then played a computer game that was designed to provoke aggression. The game involved collecting money that could be stolen by another player (who was actually a computer program). The men had the option to take revenge on the thief by making him lose money, even though this would not benefit them in any way. This was a measure of their aggression level.
The results were remarkable. The men who sniffed women’s tears before playing the game were 43.7% less likely to take revenge on the thief than the men who sniffed saline. This suggests that women’s tears have a calming effect on men’s aggression.
The Brain Mechanism Behind the Effect
The researchers also scanned the brains of the men while they played the game, using functional magnetic resonance imaging (fMRI). They found that the men who sniffed women’s tears had lower activity in two brain regions that are involved in aggression: the prefrontal cortex and the anterior insula. These regions are responsible for planning, decision making, impulse control, and emotional regulation. The men who sniffed saline had higher activity in these regions during the game, especially when they faced the thief.
The researchers also tested 62 olfactory receptors, which are the proteins that detect smells, to see if any of them could respond to tears. They found that four receptors were activated by tears, but not by saline. This means that tears have some chemical components that can be detected by the nose, even though they have no odor.
The Evolutionary Significance of Tears
The researchers speculate that the effect of tears on aggression may have an evolutionary origin. They point out that rodents also produce tears, and that female mouse tears can reduce fighting among male mice. Male mole rats also use their own tears to avoid being attacked by dominant males. These examples show that tears can act as a social chemosignal, a way of conveying information or influencing behavior through chemicals.
The researchers suggest that human tears may have evolved to protect infants from harm. They note that infants cry a lot, and that their tears may signal their vulnerability and need for care. This may elicit a protective and nurturing response from their parents, especially their fathers, who may otherwise be more aggressive or violent. The researchers say: “Tears are a bodily fluid that is produced when an individual is in a vulnerable situation where non-verbal communication is crucial.”
The researchers also acknowledge that tears may have different effects depending on the context and the relationship between the sender and the receiver. For example, tears may elicit empathy, sympathy, compassion, or pity from others, or they may be seen as a sign of weakness, manipulation, or deception. The researchers say that more studies are needed to explore the various functions and meanings of tears in human society.
