Ground squirrels do it. So do human fetuses. How did we all end up with this unhygienic habit?

Ground squirrels do it. So do human fetuses. How did we all end up with this unhygienic habit?

By now the message should be clear: Your hands are not your friends. Public health officials have told us repeatedly that putting your fingers near your eyes and mouth offers easy access to the new coronavirus. But they know it isnt easy to follow this advice. (They cant even follow it themselves.) One small study found that medical students, who really must know better, touched their faces an average of 23 times per hour during a lecture, or once every 2.5 seconds. This finding, like many others one can find in medical journals, makes a simple and prescriptive point: It tells us that were all a bunch of dirty self-inoculators, in the hopes of getting us to stop. But theres another body of research into this same behavior, and one that tries to touch on deeper questions of its origins: Could there be an evolutionary basis among human beings (and our kindred species) for this unhygienic quirk? Might the rubbing of ones face with germy digits come from primal urges that blossomed on our branch of the tree of life?
We do know its likely youve been pawing at your face since before you were even born. The well-established fact that fetuses will, in utero, touch their fetal hands to fetal faces, has led to scientific inquiry. One recent study conducted ultrasounds on 15 women from week 24 to week 36 of their pregnancies and found that fetuses were more likely to touch their faces with their left hands when the women reported feeling stressed. The same researchers published another small study hinting that the fetuses of women who smoke cigarettes might be more likely to touch their faces than those of nonsmoking women, although that finding was not statistically significant.
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The idea that stress fuels a face-touching urge has some backup from research into grownups. A study in Germany analyzed the electrical brain activity of 10 young adults while they completed a memory test, as unpleasant sounds were blasted at them from a loudspeaker. An association between the stressful sounds and volunteers grabbing (with either hand) at the nose, cheeks or chinas well as subsequent changes in their brain activityled the studys authors o to speculate that spontaneous facial self-touch helps people to regulate emotions. How might these results fit with those above, where fetuses with stressed mums face-touched with their left hands in particular? That remains a head-scratcher. (Please dont really scratch your head.)
Clearly this behavior isnt limited to humans. If youve never seen a dog cover its nose with a forelimb or a sleeping cat covering its eyes with its paws, then navigate your way to the nearest online stream of adorable animal memes. As is the case with humans, though, exactly why our furry, mammalian friends touch their faces remains difficult to decipher. One detailed study of self-grooming by ground squirrels published in the 1970s asserted that the animals face washing could be a scent-related behavior. The author noticed that the squirrels washed their faces with their forepaws, and that males would often do this before pouncing on other males in a fight. This, he thought, might be an action to help the rodents spread scents around their body from secretory glands.
We dont think about humans passing scents to one another, let alone rubbing their faces for that purpose, but a preliminary study suggests that face-touching may serve a social purpose for us, too. In a 2015 paper published in the journal eLife, Israeli scientists hooked up volunteers to devices that measured the air flow through the nose. They didnt tell the participants the reason for this, and secretly filmed the volunteers meeting people and shaking hands. The experiment showed that volunteers often brought their hands to their noses after shaking hands with other people of the same gender. And when they did so, the airflow through their noses doubled. According to the scientists, this suggests that the subjects werent scratching an itch but instead testing the scents of the people they had met. Of course these days it might be more difficult to do the same, since weve been advised against shaking hands altogether.

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