January 7, 2011
A Woman’s Tears Are a Sexual Turnoff
A chemical signal released in the tears of a crying woman may temporarily lower a man's testosterone level if he is within sniffing range of the tears, even though there is no noticeable odor given off, according to researchers from Israel's Weizmann Institute of Science and the Wolfson Hospital near Tel Aviv.
It is the first such signal researchers have found in human tears, and it's probably not unique to just women's. Theirs were just the first to be studied."It's hard to get men to volunteer to cry" in a lab, Weizmann neurobiologist Noam Sobel told the Associated Press (AP). Sobel is the senior author of the study appearing in Friday's edition of the journal Science.
Tears produced from an emotional experience are chemically different than those produced when you get dust in your eye. But biologists have long wondered about what true function emotional tears hold: Are they merely therapeutic, or do they also have some physiological role?
Mice can produce a tear that contains pheromones, odorless molecules that trigger basic instincts in many animals. So Sobel and his colleagues tested whether human tears can similarly convey subliminal chemical signals through the nose. After all, we tend to hug a crying loved one, putting our nose near their tears.
The team had women volunteers sit and watch a sad movie in the lab and then collected their tears in a vial. For a comparison, researchers dripped saline on the women's cheeks and also collected those droplets.
It was no surprise that men couldn't smell any difference between the real tears and the saline impostors.
The team then conducted a series of tests. Men were given women's photographs to rate. When they sniffed actual tears, they found the women less sexually attractive than when they sniffed saline. What surprised the researchers, was when men sniffed the actual tears they did not feel empathetic.
Also, saliva test of testosterone levels found a drop in that hormone after they sniffed tears but not the salt water. Finally, when the men sniffed tears and then watched a sad movie inside a brain-scanning MRI machine, men showed less activity in neural networks associated with sexual arousal.
Dr. Esen Akpek of Johns Hopkins University's Wilmer Eye Institute, who wasn't involved with the new study, told AP's Lauran Neergaard that tears have never been studied in this way before. "This is really interesting."
She said the findings make sense, though, because the glands that secrete tears have receptors, or docking ports, for sex hormones -- a connection most clearly seen with dry eyes, which is most common in postmenopausal women.
Why would our tears have evolved a "chemo-signal" to function as a sign of sexual disinterest? It's possible that's a proxy for lowering aggression, acknowledged Sobel, who now is trying to identify the molecule doing the work.
His findings suggest "the signal is serving to time sexual behavior. It is a signal that allows its user to say, 'Now is not the right time.' I predict there are other signals that say, 'Now it is,'" said Sobel. "This is just one of many chemo-signals."
Looking beyond the sexual drive connection, Sobel and colleagues hope the findings will one day be used in cancer treatment.
"There are a number of illnesses that are treated by lowering the levels of testosterone, the most prominent is prostate cancer," Sobel told Reuters.
Current methods for testosterone reduction cause side effects, and the research team hoped that the use of tears could eliminate them.
Instead of boosting empathy, when men were exposed to women's tears, their heart and respiratory rates, salivary testosterone and brain scans all pointed to a reduction in sexual arousal.
"Communication is key to survival. Humans, like all mammals, use smell in their communication. It is very efficient if you have a chemical signal which transmits what you want -- or clearly don't want -- in a sexual situation," Sobel added.
The researchers had also intended to study men's tears, but only one man had responded to a notice put up on Israeli college campuses asking for volunteers that could cry easily.
"This study raises many interesting questions. What is the chemical involved? Do different kinds of emotional situations send different tear-encoded signals? Are women's tears different from, say, men's tears? Children's tears? This study reinforces the idea that human chemical signals "“ even ones we're not conscious of "“ affect the behavior of others," said Sobel.
Charles Darwin, who was puzzled by human emotional crying in the 19th century, identified functional experiences to most emotional displays. For example, the tightening of the mouth in disgust, which he thought originated as a response to tasting spoiled food. But the original purpose of emotional tears eluded him.
The current study has offered an answer to this riddle: Tears may serve as a chemo-signal. Sobel points out that some rodent tears are known to contain such chemical signals. "The uniquely human behavior of emotional tearing may not be so uniquely human after all."
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