How Tears Affect Male Aggression?

The act of witnessing someone shedding tears often evokes a profound emotional response. However, a recent study, unveiled on Thursday and conducted by the Weizmann Institute of Science in Israel, introduces a captivating revelation: human tears themselves carry a chemical signal capable of dampening brain activity associated with aggression. This groundbreaking research, published in PLOS Biology, a prominent US science journal, focused on female tears due to the availability of willing donors. The authors, however, assert that the observed effects are likely not dependent on gender.

Drawing inspiration from studies on rodents, where tears serve as social signals influencing behavior, the researchers aimed to explore whether a similar phenomenon occurs in humans. In their investigation, a team led by Ph.D. student Shani Agron exposed 25 male volunteers to either “emotional” tears or a saline solution, the latter serving as a control. Notably, the participants remained unaware of the substances, as both are clear and odorless.

The tears used in the study were collected from six female volunteers who watched emotionally charged films in isolation. Using a mirror, they captured the liquid in a vial as it streamed down their cheeks. Agron explained the gender bias in tear donation, stating, “When we looked for volunteers who could donate tears, we found mostly women because, for them, it’s much more socially acceptable to cry.”

The rationale behind focusing on male participants stemmed from previous research indicating that tears reduce testosterone levels in men. Since decreasing testosterone has a more pronounced effect on aggression in men than in women, the researchers strategically chose to explore the impact of tears on male subjects first.

This study not only sheds light on the chemical signals within tears but also underscores the intricate interplay between emotions and physiological responses. Furthermore, it opens avenues for future exploration into the broader implications of tears as potent communicators of emotional states in human interactions.

In an intriguing exploration of the interplay between emotions and chemical signals, the researchers engaged volunteers in a computer game, a well-established tool in prior aggression studies. The game involved the accumulation of money while participants faced a fictitious opponent who could potentially pilfer their earnings. A unique twist allowed participants to exact revenge on the opponent by causing them financial losses, even though the participants themselves would not benefit from their adversary’s misfortune.

Following the exposure of male volunteers to either “emotional” tears or a saline control, the researchers observed a substantial 43.7 percent reduction in revenge-seeking, aggressive behavior within the game when the men had sniffed tears. This intriguing outcome mirrored findings observed in rodents. However, humans lack a vomeronasal organ, a structure present in rodents that detects odorless chemical signals and was lost during human evolution.

To decipher the mystery behind the impact of tears, the researchers conducted laboratory experiments, applying the tears to 62 olfactory receptors in a controlled setting. Remarkably, four receptors were activated by tears but not by the saline solution, shedding light on the chemical composition of tears and their potential role in signaling emotional states.

Further delving into the physiological aspects, the scientists employed MRI scanners to observe the brains of the male participants during the game. The imaging revealed heightened activity in the prefrontal cortex and anterior insula—regions associated with aggression—when men were provoked during the game. However, this aggressive response was notably dampened when participants had been exposed to tears.

In their conclusions, the researchers pointed out the prevalence of crying in close-range interactions, highlighting the cross-cultural theme of “kissing teary cheeks.” They suggested that emitting chemical signals to mitigate aggression might be particularly crucial in contexts where verbal communication is limited, as is often the case with infants. This research not only unveils the potential pacifying effect of tears on aggressive behavior but also prompts contemplation on the evolutionary significance of tear-induced chemical signaling in human communication.

Resources

1. ^{ONLINE NEWS} Phys.org. (2023, December 25). A whiff of tears reduces male aggression, says study. Phys.org. [Phys.org]
2. ^JOURNAL Agron, S., De March, C. A., Weissgross, R., Mishor, E., Gorodisky, L., Weiss, T., Furman‐Haran, E., Matsunami, H., & Sobel, N. (2023). A chemical signal in human female tears lowers aggression in males. PLOS Biology, 21(12), e3002442. [PLOS Biology]

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