“We’ve identified that there is a chemosignal in human tears,” said Noam Sobel, a neuroscientist at the Weizmann Institute of Science near Tel Aviv. Sobel headed the study, which involved exposing men to tears collected in vials. It was published online Thursday by the journal Science.
Historically, tears have been of more interest to poets than scientists.
“Emotional tears” are considered by many biologists to be uniquely human. They’re known to have a different chemical composition than tears shed when the eye is simply irritated. The few studies of tears’ psychological effects suggest they have a help-soliciting function.
Whether the quenching of ardor is a big part of their evolutionary function or a side effect of a more complicated care-giving response isn’t known. But it now seems clear they contain substances that work unconsciously on others.
For practical reasons, Sobel and his colleagues have studied only women’s tears. But they suspect that men’s tears, and possibly children’s, also contain chemical signals and are eager to find out what messages they may convey.
“This experiment opened gazillions of questions. It opened way more questions than it answered,” Sobel said.
The new study places human tears in a family of fluids that includes urine and anogenital gland secretions.
Those fluids contain behavior-altering compounds, known as pheromones. Research in rodents has shown that liquids secreted from glands near the eye have a variety of social effects. In mole rats, they reduce aggressiveness in head-to-head underground confrontations. In mice, they stimulate aggression between males but promote mating behavior between males and females.
“What we have found is that human emotional crying may not be so unique after all,” Sobel said. “It is a reflection of something common to many if not all mammals, which is chemosignaling through lacrimal secretions.”
The study, which entailed collecting tears and exposing people to them in a laboratory, was greeted positively by the small circle of researchers who study crying.
“It’s the first report. I think it’s quite interesting,” said Robert R. Provine, a psychologist and neuroscientist at the University of Maryland Baltimore County, who has studied tears as visual cues.
“The results indeed are fascinating,” said Ad Vingerhoets of Tilburg University in the Netherlands, who has studied social reactions to crying. However, he said, he suspects that tears’ pheromones may have a bigger effect on another hormone, oxytocin, which is associated with social bonding, than on testosterone. He said he hopes further research will head in that direction.