People hugged to welcome the spring equinox last month on the outskirts of Mexico City. (Edgard Garrido/Reuters)
Mary Jo Murphy is an assistant editor for Outlook and PostEverything at The Washington Post. She was an editor for more than 20 years at The New York Times.

The unwritten rule can be as indelible as any chiseled into a tablet. That’s its genius and its curse. But because norms recalibrate, and today’s are still sorting themselves out, not everyone got the invisible memo that says a person shall not hug, pat, brush, graze, stroke, clasp, rub, squeeze or nuzzle another without first obtaining or at least intuiting consent.

Joe Biden certainly didn’t get that memo. He has operated on his own tactile terms for years, and now he faces an unexpected hurdle as he ponders a twilight run for the White House. Several women have said that when Biden’s exuberant greetings or gestures of support involved touching them, they felt uncomfortable, leading some progressives to hint that he should sit this one out.

Manhandling, assault, uninvited sexual touching — that sort of contact has long violated social norms (as well as laws). But the move to regulate behavior that makes people “uncomfortable”? This treads on newer turf. Life presents “uncomfortable” moments daily, after all, and they differ from person to person. Should rejecting discomfort be the new norm? Should it be what makes me uncomfortable? Which comfort level should dictate? Good luck finding the line of demarcation. Even if we could, such a taboo would set up a Blakeian battle pitting innocence against experience. “Someone should put the bloody brakes on it,” says Francis McGlone, a neuroscientist at Liverpool John Moores University and an evangelist for social touch.

Norms governing touch are headed to a place where they can cause harm, says McGlone, who studies C-tactile afferents, the nerve fibers that respond to gentle touch. C-tactile afferents are “beautifully, exquisitely evolved,” McGlone says, and without the touch that they respond to, babies have weaker neural responses and longer hospital stays and do not gain as much weight. But the benefits derived from this nerve fiber — he’s fond of calling it “the Higgs boson of the social brain” — don’t end in infancy. McGlone points to higher rates of mortality among lonely people, who make up a large proportion of the elderly. What do the lonely elderly have in common? They don’t get touched, he says. “Don’t piss around with 3 million years of evolution,” McGlone admonishes. It “doesn’t make mistakes.” Social touch is “a biological necessity.”

What’s clear to biologists may be less so to sociologists, psychiatrists and even behavioral economists. Humans require social touch, but the rules that govern its deployment are not biologically determined. All social borders are social constructs, says H. Peyton Young, an economist and game theorist at the London School of Economics. Norms are “informal cultural understandings” born of repeated experience, Young says. They develop in “bottom up” fashion. “Somebody does something differently, and then somebody else does it, and it starts to spread.” That’s how a new norm is baked. It’s almost wholly experiential, and no authority can proclaim a norm and expect it to take hold.

Young, who wrote a paper on the evolution of social norms, cites table manners as an example of how a norm violation is perceived. In American society, people assume that you don’t start to eat before everyone else. That’s not written; it’s understood. When you see the person next to you pick up their peas with their hands, you feel uncomfortable: What’s this supposed to mean? “When a norm is in place, everything is fine because there is no discordance — the expectations are going along,” Young says. “When there’s deviation, that’s when the worries come in.”

The feelings of the women who were “uncomfortable” when Biden touched them are valid and understandable. But those feelings do not decree norms. If lots of people continue to accept hugging and other kinds of nonsexualized social touch as something they’re comfortable with (even if they’re not enthusiastic about it), then the norm will and should remain with the huggers, especially considering that biology loves a gentle touch.

Biden himself was quick to adopt the “shifting norms” narrative in the video he posted on Twitter following the complaints about his flesh-seeking hands: “Social norms have begun to change. They’ve shifted, and the boundaries of protecting personal space have been reset, and I get it, I get it.” But norms are tough to shift across large societies. “You have to have the interactions in these relatively small, coherent groups in order to learn” a norm, Young says. “I think the fact we live in an amazingly diverse society with connections across groups makes it harder to know what the norm is here.”

That’s certainly true for social touch. If it seems, anecdotally, that reactions to Biden’s hugginess have split along generational lines, with the boomer cohort tending to shrug it off and the millennial cohort tending to call it out, that might be because norms are akin to language. Older people transmit norms to younger ones, but when adolescents leave their homes, they interact with more young people and begin to create new norms, just as they create new language.

As far as touch goes, the scientific literature is not complete or conclusive, according to Juulia Suvilehto, a researcher in psychiatry at Oxford who studies social interaction. But humans are quite adept at using social touch to convey even complex messages. In a 2013 DePauw University study, for instance, researchers asked participants to convey emotions such as sadness, gratitude and fear using only touch. The recipients of the touch were blindfolded. “On average,” Suvilehto said, “the blindfolded participants were really good at decoding the intended emotion, even in the absence of any visual information or any contextual clues. So it seems that we have, for the need of a better term, a ‘touch syntax’ that research may not be great at capturing but people know very well how to use in their communication.” She adds that the intimacy of your relationship with a person shapes your comfort level and that according to one theory, touches that convey a message “that is incongruent with the relationship are the ones that are experienced as most uncomfortable.”

The existence of disparate comfort levels suggests the difficulty we have in deciding what the norm is. Norms don’t change fast, but they do change. After visiting England in the 15th century, the Dutch scholar Erasmus reported: “Wherever you go, you are received on all hands with kisses; when you take leave, you are dismissed with kisses. If you go back, your salutes are returned to you. When a visit is paid, the first act of hospitality is a kiss, and when guests depart, the same entertainment is repeated; wherever a meeting takes place there is kissing in abundance; in fact whatever way you turn, you are never without it.”

Erasmus recommended this England. Biden would have fit right in. But where was the famous British reserve? The norms clearly shifted. Molly Livingston, a lecturer in English at Kennesaw State University, took Erasmus’s description as her starting point when she wrote her dissertation on the politics of female touch in 19th-century British literature. Despite the rigid rules of Victorian society, women touched constantly in the era’s novels, walking arm in arm, or with arms wrapped around one another’s waists. You wouldn’t see that sort of social touching now, even though we live in far less reserved times.

In an article in Granta in February, Poppy Sebag-Montefiore, an English documentarian and author, wrote about living in Beijing in the early 2000s: “Every day I was touched. Many times, by friends, by strangers, by the lady who swept the street by the courtyard where I lived. By the water sellers, the restaurateurs, by old men playing chess, by people I didn’t know. Most I would never meet again. I was handled, pushed, pulled, leaned upon, stroked, my hand was held.” She marveled at how “touch had its own language, and the rules were the opposite of the ones I knew at home.” She observed that “if people bumped or rubbed arms as they passed in the street there was no need for an apology, not even a flinch. Strangers would lean their whole body weight against one another in a queue. Everyone seemed to have a certain kind of access to anyone else’s body. Shoppers and stallholders would hold on to each other’s arms as they negotiated with one another.”

This was the norm in Beijing nearly 20 years ago. But it did not survive the urbanization of the city in the run-up to the Olympics there, and when Sebag-Montefiore returned in 2008, she saw that “touch was relocating from the street to the home, from public to private life. It was becoming privatised and sexualised.” The modern world had bulldozed in, taking touch with it. She missed it.

Francis McGlone acknowledges that there are people with predatory intentions who touch inappropriately. “These people don’t help the rest of us in having a more comfortable attitude toward physical contact,” he says. Every toucher is “tarred with the same brush.”

Yet it’s a slippery slope to say that what makes someone uncomfortable should be outlawed in the unwritten book of norms, because there is great diversity in what people find uncomfortable. The norm by its nature will account for that flexibility. McGlone is right that the minority of “blatant transgressors” shouldn’t fuel a hysteria about touch that discourages nursery school teachers from hugging tots, and caregivers from offering comforting hugs to patients — and politicians from working those crucial C-tactile afferents on the public stage.

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