Handshake: More than Meets the Eye
It turns out that a handshake conveys more than it appears on the surface. People obviously make assessments through touch and sight as part of a handshake, but it turns out smell may play a more important role than previously thought.
Noam Sobel of the Weizmann Institute of Science, in Israel, took note of an observation made by epidemiologists in 2008 about just how often people touch their faces. Dr. Sobel had a hunch that it might have something to do with the gathering of scents — and could thus bear on the question of whether human beings secrete odiferous signalling molecules, sometimes known as pheromones. To test this idea his team invited 280 volunteers into their laboratory for an undisclosed experiment. The volunteers were first asked to wait alone for a few minutes. Then an experimenter (taken from a pool of 20 men and women) greeted them with or without a handshake, explained that the trial would start soon, and left. Little did the volunteers know that the experiment, details of which appear this week in eLife, had long since begun. They were being filmed the whole time.
Dr. Sobel and his colleagues measured how often volunteers placed their hands near their faces before and after the greeting, and whether this differed between those who had shaken hands and those who had not. They found that people who had been greeted with a handshake touched their faces more often than those who had not been, and also that such face-touching tended to be closer to their noses. To find out whether face-touching was accompanied by sniffing, as Dr Sobel’s hypothesis would predict, the team fitted another group of volunteers with gizmos that measured nasal airflow, and repeated the experiment. They discovered that the rate of flow more than doubled when volunteers touched their faces: a clear sign that they were smelling something.
Not all of Dr. Sobel’s observations make immediate sense. If the purpose of sniffing is to learn something about the person with whom you have just shaken hands then it would be expected that the hand sniffed was the one which did the shaking. That, though, was true only when the shakee was of the same sex as the shaker. Those who shook hands with someone of the opposite sex more often smelled the hand that had not done the shaking. Dr. Sobel does not, at the moment, have any idea why that might be the case. Nor does he know which chemicals, carrying what information, are being transferred. He has though done a few preliminary experiments to show that molecules such as squalene, hexadecanoic acid and geranylacetone — known to be chemical signals in some other species — can indeed be passed on by a simple handshake.