My own theory (that may be shared but I don’t see posted here) is that tickling is a beneficial trait that evolved through evolution. Tickling is a form of “pl

My own theory (that may be shared but I don’t see posted here) is that tickling is a beneficial trait that evolved through evolution. Tickling is a form of “play fighting”, except it is done with parents and sometimes friends. It is sometimes uncomfortable for the tickled but they giggle anyway - which encourages the tickler to keep going with the “attack”. If the ticked person had the “appropriate” response of pain, the attack would stop. The tickled thus learns reflexes to defend against attacks in general, especially against an unfriendly human. I’d imagine that the ticklish trait evolved and imparted that population an advantage against populations that were not ticklish.