Shaking a person’s hand is so routine it seems meaningless. But as it turns out, this gesture could be more than a social courtesy: it could be humans’ way of coming into contact with another person’s smells.
Just about every mammal sniffs newcomers to find out who they are and where they’ve been – but for humans, an introductory sniff is clearly taboo. And yet, as a team led by Noam Sobel, Chair of Neurobiology at the Weizmann Institute of Science in Israel has just found, we may sniff out newcomers too – except that we do it on the down-low, by checking out the scents left behind by a handshake.
As anyone who lives with a dog or a cat knows, introductory sniffs play a major part in animal greetings. This has led many researchers to claim that humans also communicate with similar chemosignaling molecules. And while previous experiments have found that human emotional responses, and even biological cycles, can fall into sync as a result of chemical communication, researchers still have little direct evidence of how humans actually transfer chemosignals from one person’s body to another.
Sobel’s team suspected that the answer might be right under their noses. Almost all humans on Earth perform some kind of handshake when greeting – even in cultures where close bodily contact with strangers is taboo. And while the common story holds that handshakes developed as a way to show a stranger that you weren’t carrying a weapon, Sobel and his team wondered if the roots of this ritual might lie even further back in our evolutionary past.
Anecdotally, Sobel and his team members had seen people sniff their hands in social situations. So they set up some experiments to find out whether that sniffing increased following a handshake.
The team started by testing whether human hands carried significant amounts of any chemicals used in chemosignaling. They had people put on rubber surgical gloves and shake hands with others, and then tested the gloves’ surfaces with a chemical detection technique known as mass spectrometry. They found that the levels of several common chemosignaling molecules on the gloves had risen, showing that handshakes definitely do transfer these molecules from one person’s hand to another’s.
Next, the team investigated whether people actually sniff the chemosignals deposited onto their hands. They recruited a sample group of 280 people, separated them into randomized groups of 20, and put them in a waiting room – which was actually an experimental room equipped with a hidden camera. After 80 seconds, a researcher came into the waiting room, introduced himself, and shook hands with half of the volunteers.
As the researchers watched the scene unfold on hidden camera, they watched for any sign of hand-sniffing behavior, however subtle. As it turned out, 55 percent of the volunteers sniffed their hands at some point, for an average of about five seconds for the right hand, and about 12 seconds for the left. In other words, people had one hand or the other near their noses for about 22 percent of the time they sat waiting. With the help of a small breath detector, the researchers were also able to verify that people actually do sniff their hands – not just bring them close to their faces.
In both men and women, a handshake from the same gender increased their tendency to sniff their shaking hand by a striking 136 percent – and what’s more, after the researchers tainted peoples’ wrists with chemosignaling molecules from the opposite gender, this correlation nearly disappeared. This means that when we shake the hand of someone of the same sex, we’re clearly interested in something about their scent.
As intriguing as these results are, Sobel calls them “only the tip of the iceberg,” and says this handshake chemosignaling may be influenced by a wide variety of other factors, including the relative social status of the people who shake hands, as well as their sexual orientation, their age, and even the presence of other chemical cues in the area.
If we’re able to gain a clearer understanding of what these signals mean to us, and how our brains process them, we may be able to analyze why humans bond – and why those bonds fall apart – more precisely than ever before. This could have an impact not only on the interpersonal level, but also on the level of large populations that just can’t seem to communicate.
So it may turn out that, just as our parents taught us, a good handshake really does matter.
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