BEFORE THE INDUSTRIAL REVOLUTION, PEOPLE SLEPT DIFFERENTLY THAN WE DO TODAY. “THE NIGHTTIME SLUMBER TO WHICH WE ASPIRE, NOT ALWAYS SUCCESSFULLY, IS CONSOLIDATED,” SAYS ROGER EKIRCH, A VIRGINIA TECH HISTORY PROFESSOR. “BUT THE DOMINANT FORM OF SLEEP FROM TIME IMMEMORIAL HAS CONSISTED OF SEGMENTED SLEEP.”

Combing diaries, medical texts, and court records, Ekirch found more than 500 references in a variety of languages to a bimodal sleep pattern. The two intervals were bridged by an hour or more of wakefulness shortly past midnight, during which people did “anything and everything imaginable,” from reciting prayers to pilfering a neighbor’s chickens.

“The way we sleep today,” says Ekirch, “is a remarkably recent phenomenon, the consequence of modern technology—bathing ourselves in electric light, which reconfigures the human body clock—coupled with cultural priorities that regard sleep as a necessary evil.”