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Tickling is a rather interesting phenomenon: When humans or apes are touched in certain areas like the armpits or sides, we respond with laughter AND frantic attempts to stop the assault. Obviously our ticklish areas tend to be very vulnerable, so it makes sense that we would want to protect ourselves, but why do we respond with laughter? How might both of these reactions to tickling have evolved? Do they have the same evolutionary purpose or different ones?

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I have heard that rats are also ticklish, so apparently it is not limited to primates. – so12311 Feb 15 '12 at 0:45

Tickling probably evolved from a defense mechanism but then gradually changed into a more social action, as explained in Provine, 2005 (PDF):

The neurological mechanism of tickling probably evolved from a reflex defense mechanism that protects our body’s surface from external, moving stimuli, probably predators or parasites. Our response to tickle is more varied and complex than the typical reflex, but it has some stereotypic, reflex-like properties (i.e., we laugh when tickled, struggle to escape the tickler, huddle, fend off the tickling hand). Although you can be tickled to laughter by a machine (Harris, 1999) (PDF), most everyday tickle is yet another social context for laughter and a form of communication.

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Actually I find the phenomenon of laughing itself a bit intriguing. Does anyone know how laughing evolved? I think we need to understand that before trying to find an explanation for how why tickling needs to laughter. – Vinayak Pathak Feb 12 '12 at 14:47
@VinayakPathak - This answer talks about that. – Bobson Sep 22 '14 at 14:36

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