The idea of having to lick the same lollipop as a stranger is likely to elicit a lot of disgust. We only exchange saliva with people we really like. Even babies know that. According to scientists at Harvard University, babies and toddlers use it as a trick to figure out who to trust.
After nine months in a safe cocoon, babies enter a whole new world that they don’t understand. Slowly but surely they learn to understand everything. Apparently, infants even have a handy method for checking which people have a close relationship. The key word: saliva. When people exchange spit — by kissing, sharing an apple, or drinking from each other’s glasses, for example — they must have a close bond.
Two actresses and a doll
This is shown by an experiment by Ashley Thomas, a researcher at Harvard University and MIT (Massachusetts Institute of Technology). She let dozens of children between the ages of 8 and 19 months watch a film. The video featured two actresses and a hand puppet. One woman ate an orange slice and then gave it to the doll. Or yes, of course she pretended. The other woman played with a ball and threw it at the doll. A little later, the doll began to cry, and the babies and toddlers immediately looked at the actress who had shared the orange, as if they expected her to take care of the crying doll.
Then the crying doll was replaced by a new one, which also started crying after a while. Then suddenly there was no difference anymore: the children looked at both actresses.
Of course, it could be that the children thought that one woman was just sweeter than the other because she shared a treat with the doll. To rule this out, the experiment was repeated. This time, the first actress had to put her finger in her mouth, and then into the doll’s mouth. The other actress just had to touch her forehead, and the doll’s. The result was exactly the same: when the doll started whining, the eyes immediately turned to the first lady.
We all don’t really like other people’s saliva. The same goes for spit. Except when it comes to your own baby, but what if your baby spits up too much? Parents of Now answers.
Congenital disgust
For the little ones, things like hugs or emotional support are important signs that people are close. But exchanging saliva is also one of them. And that’s important, because that’s how children know who they can count on when they’re scared or need someone. Thomas writes that in the scientific magazine Science.
(Read more below the photo.)
The question is: how come? Thomas and her colleagues think it’s a kind of innate insight, an evolutionary advantage so babies can discern which people to trust. But there could also be another explanation.
Psychologist Christine Fawcett, of Uppsala University in Sweden, has written a commentary on the study. She says people have a built-in aversion to sharing spit. Worldwide we find that very dirty. Only for our own child, or loved ones and best friends, do we make an exception and think it’s okay to kiss. And also very exceptional: to share cutlery or a toothbrush. Babies see that and just adopt the behavior.
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