Why Do Guys Always Have to Pat Each Other on the Back When They Hug?

Male-to-male greeting in America takes many forms. There’s the classic handshake. The fist bump. Dap. The head nod. The you-too-huh? shrug from across a baby shower.* But as the world of masculine salutations takes on new layers of complexity—reaching its most evolved form in Cleveland—there is one fixed practice that remains something of a universal truth: When hugging, two (usually) heterosexual men will almost always pat each other on the back.

Start paying attention, and you’ll see it everywhere. We can’t help it, as if it were a particularly pernicious tic or social crutch, like constantly checking your phone during dinner or hitting a vape. And though the most commonly accepted explanation is true—that a not insignificant part of it is born out of the admittedly primitive heterosexual norms that deem tenderness among males not “masculine” (more on that to come)—there must be some deeper anthropological basis for slapping another guy on the back. And, according to experts, there is!

But first, we need to set the table: Why do we even hug?

*Honestly, I’ve only heard that this happens. I’ve never been to a baby shower—haven’t even held a baby, while we’re being open with one another. Seems like too much risk (dropping it) for a non-reward (holding a baby).

“As forests receded, we were no longer forest-dwelling apes but upright hominids on a plain,” says Mark Bowden, human-behavior and body-language expert. “We can now see a distance, and so we need clear signals that somebody is a friend or a predator. So open body language and open palms—imagine hands up, that big surrender gesture—somebody can see two miles away that you’re not a threat.”

This “Look, I’m not going to stab you with a spear” measure is especially important to establish when the hominids happen to own penises.

”Testosterone makes people more risk-tolerant,” says Bowden. “So you will get more aggression the more testosterone [there is], not because the testosterone is making somebody more aggressive. What it’s doing is lowering the idea of there being a risk in the first place… [So] groups of males, on the whole, [have] a lot of behaviors to countermeasure the possibility of aggression.”

And what’s the best behavior to countermeasure the aggression when those two miles become no miles, and you’re now faced with that guy you saw in the hazy distance 20-some minutes ago, across the plain? Sure, a handshake might work. But there’s actual value in doing something more intimate to quash any suggestion that you’re going to smack him with a cudgel and steal his collection of exotic sabertooth furs, like hugging. Take it from Richard Wrangham, who works in Harvard’s Department of Human Evolutionary Biology (and who e-mail-answered my strange request for comment after six zoos declined).

“There is a general principle involved in animal alliances, such as male-male friendships in primates: If two individuals are to express feelings of mutual solidarity, the reliability of the signal is greater if it is genuinely somewhat stressful. For example, male baboons who like each other but want to be sure about each other’s feelings touch each other’s genitals: If A can do that to B, and B doesn’t snarl back, A can be truly confident that B likes him.

“[This theory] suggests that males would basically prefer not to pat or hug, because such close physical proximity is ultimately somewhat stressful (given that it is potentially dangerous to be so close to someone who could be a secret rival). However, the stress is worth tolerating if it leads to confidence in each other’s feelings about each other.”