Jan 11, 2011

No Woman No Cry

Why do we cry when we have an intense emotional experience? This is a question scientists have wondered for a long time. Tears serve to relieve extreme feelings, but many people would agree with me that they can be very inconvenient and worse yet, when they seem to have their own life and be uncontrollable. The only vertebrates that shed tears of sorrow and joy are us, human. Dogs whine, especially out of anxiety when their master leave alone in the house, but they do not produce tears in response to emotions. Mice also "cry out" tears but they do so to secrete a chemical signal that communicates the desire to mate, quite a very different reason from humans. Aside from keeping the eyes moist and help maintain the cornea clear, it has been suggested tears function to cleanse the body from hormones that occur during times of stress.

The article published this week in the journal Science suggests a new role: the authors claim that tears are a great "turn off" for men, and that this function would serve as a mechanism to communicate rejection without words. In the study, a small group of women watched sad movies and collected their own tears in cotton balls. Then, a group of 50 men was divided into two, one that smelled the cotton soaked in the women's tears, and another one that smelled a saline solution of comparable composition. The results show that those exposed to the tears rated photographed women as less attractive compared to their peers who smelled the saline solution. In another set of experiments, a group of men exposed to the tears reported a reduction in their arousal when watching movies and videos with sexual content. Furthermore, the activity levels in areas involved in sexual arousal in the brain and the testosterone levels were lower in these men. Interestingly, in disagreement with what was expected, the empathy and mood of the men did not change at all.

The results of the study are very interesting and have caused excitement beyond the scientific community. Part of the attention is that the existence of human pheromones -chemicals that change the physiological and social behavior of an individual- are of great interest to many industries. From the producers of perfumes to those who look for explanations for war, work very hard to find the ideal odoriferous molecule for every purpose. For this reason, it is common to see signs of these molecules with 'super powers' published weekly in scientific journals.

Although the exact cause of the physiological response in men was not investigated in this study led by Dr. Noam Sobel, a cognitive neuroscientist in Israel, the team did conclude that human tears contain chemical signals. Also, they claim that their investigation reveals a new "function for human tears". Given that the article coincide with sociological studies that have suggested that tears reduce the aggressive behavior of men, it is possible that there is, indeed, a molecule with such characteristics in tears. In the same way, it is possible to find an evolutionary explanation for the development of a mechanism that reduces aggression toward oneself. However, the tears in humans are produced for a variety of reasons, from sadness to ecstasy, and their effects can be linked to the context of the situation in which the tears occur.

In the article mentioned, the tears were bound to a context of grief, and before drawing conclusions, it is necessary to investigate the effect of the tears of joy and neutral lacrimation, for example as a result of irritation. Moreover, the number of men and women in the study is too small to generalize the findings and all the volunteers who collected tears were women (men are not as good tear producers, the authors clarified). Likewise, the tears collected bathed the cheeks of the women, implying that the chemical might be on their skin and not in tears. Surely we are not the only animals invulnerable to the effects of pheromones and more work is needed to find them, but until today, it is not possible to conclude that tears are chemical signals that change the behavior of men. And we still do not know why we, humans, cry ...

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