(“Larmes (Glass Tears)“ by Man Ray.)
The study, published on Thursday in the journal Science, could begin 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 the 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 level of 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 now studying men’s emotional tears, so the scientific implications of, say, the weeping of John Boehner remain an open question. But Dr. Sobel said he believed 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 with sad tears. 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 potential 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 psychology professor at the University of Chicago 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.”
Why women’s tears would send a message of “not tonight, dear” is somewhat puzzling. Some experts suggested it could have evolved to reduce men’s aggression toward women 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 could have evolved in part to coincide with women’s 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 living together tend to synchronize menstruation, objected to that theory, saying, “Oh, please — 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 happened accidentally upon the evidence that women’s tears tell men to take 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, they assembled a “bank of criers,” Dr. Sobel said: “six women who were really good” at bawling their eyes out, plus several “backup criers.”
He said, “We had to use fresh tears,” no more than two hours old, so criers were called on frequently to sob a renewed supply. The women, roughly 30 years old, watched scenes from their favorite tear-jerkers, including “Life Is Beautiful,” “My Sister’s Keeper,” “When a Man Loves a Woman,” and an Israeli movie, “Broken Wings,” said Yaara Yeshurun, a doctoral student on the team. She was also one of the criers, losing it over “Terms of Endearment.”
As a control, researchers trickled saline down the women’s faces, also collecting that in vials. Tears and saline were dribbled onto pads that were then affixed below men’s nostrils, approximating the close contact a man might have when hugging a teary-cheeked woman. The men, in their late 20s, each sniffed tears one day and saline another day, without knowing which was which.
In one experiment, tear-sniffing made men more likely to rate women in photographs as less sexually attractive. In another, to establish a context of sadness, men watched a scene from “The Champ” after sniffing tears or saline. Both sniffers became equally sad, but tear-sniffers showed less sexual arousal and lower testosterone.
Finally, researchers turned to brain imaging. They showed men scenes from “9 ½ Weeks” — specifically, from the more explicit European version, which, Dr. Sobel said, “has been validated as being particularly arousing.” Functional M.R.I. scans identified brain areas reflecting arousal. The men sniffed tears or saline, and watched sad movies. Tear-sniffers showed less activity in those same brain regions.
The studies were financed by the Minerva Stiftung Foundation, a German-based organization supporting research involving Israeli and German scientists, often with money from the German government.
Many unanswered questions remain, including whether results can be replicated by other researchers. What substance could comprise the chemical signal? And is it perceived through the nose or another way?
Dr. Sobel, who also plans to study children’s tears, said the substance might be a protein or steroid and is most likely perceived nasally. And citing another research team’s study showing that when blind mole rats wash their faces with tears, it reduces aggression in other males, Dr. Sobel wonders if other animals’ tears could have chemo-signaling effects.
William H. Frey II, a biochemist who showed that the chemical composition of emotional tears is different from that of reflexive tears, said he was “thrilled to death to see somebody doing something on the chemistry of emotional tears,” and added that the results could be compatible with his theory that crying involves shedding stress-related toxins.
But Dr. Frey, director of the Alzheimer’s Research Center at Regions Hospital in St. Paul, said that more must be understood, including why sexual dampening would occur. Evolution might favor less sexual assertiveness toward a crying mate, he said, but if a woman’s tears are brought on by an attacker, “is a husband with less testosterone going to be more or less aggressive in defending his family?”
Still, Dr. Provine said the findings were “consistent with other proposed roles of tears, including solicitation of caregiving and reduction of aggression.” He added: “That tears are de-arousing would not be a surprise to most men. I can’t think of anything I’d rather do less than go see a tear-jerker.”
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