So tickling serves a twofold purpose by identifying you as an individual, but also an individual in need of social interaction. "Laughter," Provine says, "reveals us as a social mammal, stripping away our veneer of culture and language, challenging the shaky hypothesis that we are rational creatures in full conscious control of our behavior."
By feeling a tickle, then tickling someone else and seeing their reaction, toddlers may begin to glimpse themselves as entirely new beings, a conceit that will accompany them for the rest of their lives. In fact, tickle battles occur even before toddlers recognize themselves in mirrors and begin to use first-person language like "I, me, and my."
And, to return to the dark side of tickling, what is torture if not an attempt to take away a victim's sense of self, a sense which produces the will to live? Tickle torture undermines humans' most basic sense of self and joy.
Tickling, then, may not just be some weird quirk in our brains, or even a lingering defense mechanism from our early ancestors. It may be how we develop our entire sense of being. Think about that the next time someone tries to tickle you.