For the past 30 years, I’ve begun every course that I teach by shaking each student’s hand. If it’s a big lecture class, I stand at the door and shake their hands as they come in; if the class is small, I walk around the room and greet each student individually.

That’s my way of showing that they exist, and that they matter. But it’s also a way to establish my own importance; after all, no one else in the room is shaking everyone’s hand. That’s the paradox of the handshake, which demonstrates our shared humanity as well as the power we wield over other human beings.

And that’s also why President Trump can’t seem to wean himself off the practice. A self-described germaphobe, Trump has called handshaking “barbaric” and “one of the curses of American society.” But even after health officials warned that it could spread coronavirus, Trump has kept doing it. It’s how he shows he’s the top dog.

Witness last Friday’s news conference at the White House, where Trump shook hands with all but one of the CEOs who had come to the event. The lone holdout extended his forearm for an elbow bump, surprising the bemused president. “Okay, I like that,” Trump said, with a laugh. “That’s good.”

But not good enough for Trump, apparently. “You can’t be a politician and not shake hands,” Trump said, earlier this month. He was echoed by his ever-obsequious vice-president, Mike Pence. “As the president has said, in our line of work you shake hands when someone wants to shake your hand,” Pence said. “I expect the president will continue to do that. I’ll continue to do it.”

Never mind that viruses spread more easily via the hands than the lips; even the European “double-kiss” is probably safer than a handshake. So are a variety of other hand-related greetings. In 2014, scientists demonstrated that a high-five transmitted half as much bacteria as a handshake, and a fist bump only a tenth as much.