On Wednesday, the former vice president and potential presidential candidate Joe Biden released a video in which he discussed the importance of personal space. “Social norms have begun to change,” he said. “They’ve shifted, and boundaries of protecting personal space have been reset — and I get it.”

Mr. Biden was responding to allegations by two women that he made them uncomfortable by coming too close, and by being too familiar and hands-on. His video was, in part, an acknowledgment that the rules of social engagement can change over time — along with perceptions of how much physical contact is appropriate, and where the boundaries of personal space lie.

The dynamics of both social space and touching have been well explored by scientists. In the 1960s, American anthropologist Edward Hall laid out the basics of social space, based on field work in Europe, Asia and elsewhere .

We each reserve around us a zone of about 18 inches — “intimate space,” he called it — for close friends and family. “Personal space,” from 18 inches to about 4 feet, is open to acquaintances and colleagues. And “social space,” from 4 feet to 12 feet, is the appropriate orbit for strangers or new colleagues.