This undated handout photo provided by the journal Science shows a donor woman watching sad films in isolation, using a mirror to capture tears into a vial. If a crying woman’s red nose isn’t a big enough turnoff to a man, a surprising experiment found another reason: Tears of sadness may temporarily lower his testosterone level. (AP Photo/Science) |
Emotional
crying is a universal, uniquely human behavior. When we cry, we clearly
send all sorts of emotional signals. In a paper published online today
in Science Express, scientists at the Weizmann Institute have
demonstrated that some of these signals are chemically encoded in the
tears themselves. Specifically, they found that merely sniffing a
woman’s tears – even when the crying woman is not present — reduces
sexual arousal in men.
Humans,
like most animals, expel various compounds in body fluids that give off
subtle messages to other members of the species. A number of studies in
recent years, for instance, have found that substances in human sweat
can carry a surprising range of emotional and other signals to those who
smell them.
But tears
are odorless. In fact, in a first experiment led by Shani Gelstein,
Yaara Yeshurun and their colleagues in the lab of Prof. Noam Sobel in
the Weizmann Institute’s Neurobiology Department, the researchers first
obtained emotional tears from female volunteers watching sad movies in a
secluded room and then tested whether men could discriminate the smell
of these tears from that of saline. The men could not.
In
a second experiment, male volunteers sniffed either tears or a control
saline solution, and then had these applied under their nostrils on a
pad while they made various judgments regarding images of women’s faces
on a computer screen. The next day, the test was repeated — the men who
were previously exposed to tears getting saline and vice versa. The
tests were double blinded, meaning neither the men nor the researchers
performing the trials knew what was on the pads. The researchers found
that sniffing tears did not influence the men’s estimates of sadness or
empathy expressed in the faces. To their surprise, however, sniffing
tears negatively affected the sex appeal attributed to the faces.
To
further explore the finding, male volunteers watched emotional movies
after similarly sniffing tears or saline. Throughout the movies,
participants were asked to provide self-ratings of mood as they were
being monitored for such physiological measures of arousal as skin
temperature, heart rate, etc. Self-ratings showed that the subjects’
emotional responses to sad movies were no more negative when exposed to
women’s tears, and the men “smelling” tears showed no more empathy. They
did, however, rate their sexual arousal a bit lower. The physiological
measures, however, told a clearer story. These revealed a pronounced
tear-induced drop in physiological measures of arousal, including a
significant dip in testosterone – a hormone related to sexual arousal.
Finally,
in a fourth trial, Sobel and his team repeated the previous experiment
within an fMRI machine that allowed them to measure brain activity. The
scans revealed a significant reduction in activity levels in brain areas
associated with sexual arousal after the subjects had sniffed tears.
Sobel:
“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.”
Human
emotional crying was especially puzzling to Charles Darwin, who
identified functional antecedents 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 chemosignal. 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,” he says.
