Only humans and our close relatives are known to engage in tickling behaviour, suggesting that it may have evolved in one of our great ape ancestors. Take chimpanzees and bonobos, who often tickle each other while playing. In a study, Elisa Demuru … and her colleagues … discovered a strong correlation between tickling and age, with older bonobos more likely to be the tickler and younger ones more likely to be the ones tickled.
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For Demuru, this is a strong indication that tickling evolved as a pro-social behaviour that strengthens connections between youngsters and other members of their group. It is closely linked with play-fighting, she explains: actions that would seem aggressive or unpleasant if carried out by a stranger can be enjoyed when they are done by close relations or friends.
Even unwanted tickling can elicit laughter, regardless of one’s state of mind and relationship to the person – or machine – doing the tickling. Some researchers argue that this shows ticklishness is a physiological reflex …. A third hypothesis supposes that it helps youngsters learn to defend themselves in combat by protecting vulnerable areas of their body.
