When we cry, we may be doing more than expressing emotion. Our tears, according to striking new research, may be sending chemical signals that influence the behavior of other people.
The research, published on Thursday in the journal Science, could begin to explain something that has baffled scientists for generations: Why do humans, unlike seemingly any other species, cry emotional tears?
In several experiments, researchers found that men who sniffed drops of women’s emotional tears became less sexually aroused than when they sniffed a neutral saline solution that had been dribbled down women’s cheeks. While the studies were not large, the findings showed up in a variety of ways, including testosterone levels, skin responses, brain imaging and the men’s descriptions of their arousal.
“Chemical signaling is a form of language,” said one of the researchers, Dr. Noam Sobel, a professor of neurobiology at the Weizmann Institute in Israel. “Basically what we’ve found is the chemo-signaling word for ‘no’ — or at least ‘not now.’ ”
The researchers are currently studying men’s emotional tears, so the scientific implications of, say, the weeping of the new House speaker, John A. Boehner, remain an open question. But Dr. Sobel said he believed that men’s tears would also turn out to transmit chemical signals, perhaps serving to reduce aggression in other men.
Dr. Sobel said the researchers started with women because when they advertised for “volunteers who can cry with ease,” they could not find men who were “good criers,” readily able to fill collection vials. Fortunately, he said, “we have a male crier now.”
Several experts said the findings — besides potentially adding subtext to crying songs through the ages, from Roy Orbison to the Rolling Stones — could be a first step toward a breakthrough on a mysterious subject.
The discovery of a chemical signal in tears suggests “a novel functional role for crying,” said Martha K. McClintock, a professor of psychology at the University of Chicago who is known for her work on pheromones and behavior. “It really broadens the possibilities of where signals are coming from.”
Robert R. Provine, a psychologist and neuroscientist at the University of Maryland, Baltimore County, who has studied crying, said the discovery was “a really big deal” because “emotional tears are a very important evolutionary development in humans as a social species,” and this “may be evidence of another human pheromone.”
Many questions remain, including whether the results can be replicated by other researchers, what substance could comprise the chemical signal and whether it is perceived through the nose or another way.
Why women’s tears would send a message of “not tonight, dear” is puzzling. Some experts suggested the tears could have evolved to reduce men’s aggression toward women who are weakened by emotional stress. The studies did not measure the effect on aggression, although future research might, Dr. Sobel said. Another thought, he said, is that the effect of tears evolved in part to coincide with menstrual cycles.
“There’s several lines of evidence that women cry much more during menstruation, and from a biological standpoint that is not a very effective time to have sex, so reducing sexual arousal in your mate at that time is really convenient,” he said.
Dr. McClintock, who reported 40 years ago that women who lived together tended to synchronize their menstruation, objected. “Oh, please,” she said. “Do we know that women cry more often during menstruation?”
She said it was “premature to speculate about the evolutionary function” of chemo-signaling in tears, adding: “I have no doubt that it affected sexuality as they report, but I would be very surprised if it doesn’t turn out to affect other emotions in other contexts. Maybe it’s affecting some deeper, more fundamental psychological process that drives the effect that they’re reporting.”
The researchers accidentally happened upon the evidence that women’s tears make men feel as if they have taken a cold shower.
They had assumed chemical signals from tears would trigger sadness or empathy in others. But initial experiments found that sniffing women’s tears did not affect men’s mood or empathy, but “had a pronounced influence on sexual arousal, a surprise,” Dr. Sobel said.
Deciding to investigate more rigorously, the researchers posted fliers on several Israeli college campuses seeking easy criers. Seventy women volunteered, along with one man. But of the 70 women, there were only six “who were really good” at bawling their eyes out, Dr. Sobel said. They became the researchers’ “bank of criers”; a stable of “backup criers” was kept in reserve.
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