Tears dampen arousal
Women's tears contain a chemical signal that reduces men's sexual excitement
Human tears, once believed to be emotional signals without a biological function, actually contain a chemical that reduces sexual attraction, arousal, and testosterone levels in men, according to a new study published online today (January 6) by linkurl:Science.
"It is convincing," said linkurl:Kennedy Wekesa,;http://www.alasu.edu/academics/colleges--departments/science-mathematics--technology/biological-sciences-department/faculty/dr-kennedy-wekesa/index.aspx a biologist at Alabama State University who was not involved in the research. "Given studies of chemosignals in mice, it's not surprising that humans also have chemosignals in bodily fluids such as tears."
Previous studies have demonstrated that mouse tears contain chemosignals or pheromones -- excreted chemicals that trigger a behavioral response in other mice, such as aggression in males or acceleration of puberty in females. Yet human tears were long thought to serve simply as an emotional signal -- a communication trait unique to our species.
But three years ago, while testing the effect of tears on mood in people, linkurl:Noam Sobel;http://www.weizmann.ac.il/neurobiology/worg/ and colleagues at the Weizmann Institute of Science in Israel made a surprising observation. Male subjects exposed to emotional tears -- isolated from females crying during sad movies then deposited onto a small pad pasted above the male's upper lip -- felt no difference in happiness or sadness, but they did experience a change in another emotion: According to a questionnaire the subjects completed, "there was a pronounced drop in sexual arousal," Sobel told The Scientist.
"That's what started us off looking more carefully in that direction."
In a subsequent study, the researchers measured heart and respiration rates, skin temperature, testosterone levels and brain activity of sexual-arousal-related brain structures, in response to sniffing emotional tears, which are odorless and clear. Saline was used as a control. They recorded an overall reduction in all measures, leading the researchers to a central conclusion: Women's emotional tears contain a signal that reduces men's sexual excitement.
"This is the chemical word for 'No,'" said Sobel. "Or at least for 'Not now.'"
Sobel speculates, however, that the results may be part of a larger picture related to aggression, since lowered testosterone is also linked to lowered aggression in males. "It could be that what we measured -- sexual arousal -- is a byproduct of lowering aggression," he said. "It's easy to come up with an evolutionary reason for why it would be helpful to have a signal that lowers one's aggression toward you."
Overall, the study "raises lots of interesting questions," added Wekesa. Are there chemosignals in tears of joy or eye-protective tears (produced by cutting onions, for example)? Also, how might men react to the tears of other men, rather than women? The researchers studied only women's tears out of necessity, said Sobel: The only good criers who volunteered for the study were women.
Still, "we don't think this is something unique for women," said Sobel. "I would predict, without hesitation, that there will be chemosignals in men's tears and in children's tears, and these chemosignals will all act within, as well as across, gender."
Gelstein, S., et al., "Human tears contain a chemosignal," Science, doi: 10.1126/science.1198331
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[1st November 2010] *linkurl:New role for pheromones?;http://www.the-scientist.com/blog/display/56056/
[14th October 2009] *linkurl:Sexual communication in tears;http://www.the-scientist.com/news/20051006/01/
[6th October 2005]