Handshakes
may engage our sense of smell
Weizmann Institute of Science, Science Daily
Why do people shake hands?
A new Weizmann Institute study suggests one of the reasons for this ancient custom may be to check out each other's odors.
Even if we are not consciously aware of this, handshaking may provide people with a socially acceptable way of communicating via the sense of smell.
Not only do people often sniff their own hands, but they do so
for a much longer time after shaking someone else's hand, the study has found.
As reported today in the journal eLife,
the number of seconds the subjects spent sniffing their own right hand more
than doubled after an experimenter greeted them with a handshake.
"Our findings suggest that people are not just passively exposed to socially-significant chemical signals, but actively seek them out," said Idan Frumin, the research student who conducted the study under the guidance of Prof. Noam Sobel of Weizmann's Neurobiology Department.
"Rodents, dogs and other mammals commonly sniff themselves, and they sniff
one another in social interactions, and it seems that in the course of
evolution, humans have retained this practice -- only on a subliminal
level."
To examine whether handshakes indeed transfer body odors, the
researchers first had experimenters wearing gloves shake the subjects' bare
hands, then tested the glove for smell residues. They found that a handshake
alone was sufficient for the transfer of several odors known to serve as
meaningful chemical signals in mammals.
"It's well known that germs can be
passed on through skin contact in handshakes, but we've shown that potential
chemical messages, known as chemosignals, can be passed on in the same manner,"
Frumin says.
Next, to explore the potential role of handshakes in
communicating odors, the scientists used covert cameras to film some 280
volunteers before and after they were greeted by an experimenter, who either
shook their hand or didn't.
The researchers found that after shaking hands with
an experimenter of the same gender, subjects more than doubled the time they
later spent sniffing their own right hand (the shaking one).
In contrast, after
shaking hands with an experimenter of the opposite gender, subjects increased
the sniffing of their own left hand (the non-shaking one). "The sense of
smell plays a particularly important role in interactions within gender, not
only across gender as commonly assumed," Frumin says.
The scientists then performed a series of tests to make sure the
hand-sniffing indeed served the purpose of checking out odors and was not
merely a stress-related response to a strange situation.
First, they measured
nasal airflow during the task and found that subjects were truly sniffing their
hands and not just lifting them to their nose. It turned out that the amount of
air inhaled by the volunteers through the nose doubled when they brought their
hands to their face.
Next, the scientists found they could manipulate the hand-sniffing
by artificially introducing different smells into the experimental setting. For
example, when experimenters were tainted with a commercial unisex perfume, the
hand-sniffing increased.
In contrast, when the experimenters were tainted with
odors derived from sex hormones, the sniffing decreased. These final tests
confirmed the olfactory nature of the hand-sniffing behavior.
Taking part in the study were Ofer Perl, Yaara Endevelt-Shapira,
Ami Eisen, Neetai Eshel, Iris Heller, Maya Shemesh, Aharon Ravia, Dr. Lee Sela
and Dr. Anat Arzi, all of Prof. Sobel's lab.
"Handshakes vary in strength, duration and posture, so they
convey social information of various sorts," says Prof. Sobel. "But
our findings suggest that at its evolutionary origins, handshaking might have
also served to convey odor signals, and such signaling may still be a
meaningful, albeit subliminal, component of this custom."
Story
Source:
The above story is based on materials provided by Weizmann Institute of Science.Note:
Materials may be edited for content and length.
Journal
Reference:
Idan Frumin, Ofer Perl, Yaara Endevelt-Shapira, Ami Eisen,
Neetai Eshel, Iris Heller, Maya Shemesh, Aharon Ravia, Lee Sela, Anat Arzi,
Noam Sobel. A social
chemosignaling function for human handshaking. eLife, 2015; 4 DOI:10.7554/eLife.05154
Cite
This Page:
Weizmann Institute of Science. "Nice to sniff you:
Handshakes may engage our sense of smell." Science Daily,
3 March 2015. <www.sciencedaily.com/releases/2015/03/150303105922.htm>.