I have just discovered a profoundly human, evolutionarily crucial fact about the new baby in our house: He likes to be tickled.
This isn’t a joke. For centuries, the deepest of thinkers—Aristotle, Darwin, Shylock—have puzzled over this silliest of human acts. Robert R. Provine, a neuroscientist at the University of Maryland at Baltimore County, is their heir, and according to his new book, Curious Behavior, Shylock was on to something. Tickling is not an inexplicable physical tic. It’s central to who we are—and how we became who we are.
Provine first began researching tickling when someone came up to him before a talk on laughter—he’s an expert on the subject—and said she hoped he wasn’t studying tickling. She hated tickling. So inevitably, he decided to study it: “Her revulsion was persuasive.” If she’s that annoyed by it, he thought, it must be important.
Its importance begins in infancy. “When people say they hate being tickled and there’s no reason for it, they forget that it’s one of the first avenues of communication between mothers and babies,” he says. “You have the mother and baby engaged in this kind of primal, neurologically programmed interaction.” Or the father: I tickle my son; he shrieks; I tickle him more; he shrieks more; I tickle him yet more; he starts wailing. I apologize.
In a sense, this is our first conversation—how we manage to talk with someone despite being preverbal. The content here is socioemotional, and as a form of social binding, it preceded the development of language, Provine says. Play with a toddler and you might end up recapitulating that developmental progression: before talking comes tickling. “If one wants to become friends with a young child,” as the neuroscientist Jaak Panksepp has written, “there is no easier way to negotiate the social terrain than by gently escalating tickle games.”
Tickle games are not unique to humans. They’re part of our mammalian heritage. “Tickle is what binds mammals together in rough-and-tumble play,” Provine says. Pick a mammal. Squirrels engage in play that looks a lot like tickling. So do—of all species—elephants. So do rats: In a sensational experiment a decade ago, Panksepp recorded the ultrasonic sounds, inaudible to the human ear, that rats make when tickled by an experimenter. The rats, in other words, seem to giggle when tickled.
But only chimpanzee and human mothers gaze deeply into the eyes of their infants—and then tickle them. In the wild, chimpanzee infants will bite their mothers, who respond by tickling; the infants then bite their mothers again, which provokes more tickling; and so on. It’s a social dance: Tickling is the way we and the chimps establish, without words, that we’re in this thing together.
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.