Tickling in infancy is foundational behavior, in other words. Provine contends that tickling is at the root of not just communication but laughter. “Tickle is the primal laugh stimulus,” Provine says. It is the “labored breathing” during this sort of rough-and-tumble play that is at the root of human laughter, he argues: Over millions of years, pant-pant became ha-ha. It goes back so far that the feigned tickle is Provine’s candidate for the oldest joke in the world. It’s the only joke, he says, that you can tell with equal success to a human and a chimpanzee: They both crack up. (An actual tickle would spark a purely reflexive response, so it doesn’t qualify.)
Provine is delightfully unconcerned about being seen as a serious scientist, even though he is. (Sample Provine sentence, from a peer-reviewed journal: “Solo tickle is even emptier than solo sex—you can masturbate to climax but you cannot tickle yourself.”) Curious Behavior, which has chapters on things like sneezing and yawning, is a work of what Provine calls sidewalk neuroscience—research you can do while walking down the street. You don’t need a massive NSF grant; you need people willing to laugh into your microphone. (“If you insist on more equipment, buy a stopwatch.”)
But Provine’s basic point is very serious: He thinks that we overlook the significance of mundane or embarrassing behavior. Sometimes deep insights are found in shallow places. We yawn when other people yawn, or itch when other people itch, because these are very old, herd-driven behaviors. We are obeying what Provine calls “neurological scripts.”
And tickling, Provine says, has a profound lesson to teach us. “When you look at the evolution of the development of tickle, you’re also looking at the evolution of the development of self,” he says. What’s at work in tickling, he argues, is the neurological basis for the separation of self from other. After all, as Provine noted so indelicately, you can’t tickle yourself. Your body knows that you are you; you can’t fool it. “Otherwise you’d go through life in a giant chain reaction of goosiness,” Provine says. “You’d be afraid of your own clothing if you could never distinguish between touching and being touched.”
When a baby senses a foreign hand lightly brushing his bare feet, he’s experiencing something that is recognizably other—which means that there’s something that isn’t other, too: There’s himself. Tickling is central to who we are, because it is part of how we establish that there’s a we there. (This may be why too much or unwanted tickling is so viscerally frightening and overwhelming: There’s the sense that someone is invading your body and you can’t stop it.)
It’s exhilarating to think about all this while I’m tickling my infant son. (Until he starts wailing, that is.) But there is a cautionary tale to Provine’s tickling research: Like hiccupping, the amount of tickling in your life diminishes with each passing year. Tell me how much you are tickled and I can tell you how old you are. After the age of 40, Provine says, the frequency of tickling drops tenfold.
I tell myself that tickling my son is keeping me young. And Provine tells me that the ramifications of not being able to tickle yourself—the link between tickling and the perception of self—haven’t been fully pursued yet. So with every diaper change, for the sake of science, I pursue those ramifications.
At press time, the research seemed to be going well.