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Historical records contain evidence of biphasic sleeping habits in humans dating back hundreds of years.

Before electricity, people typically went to sleep about two hours after the sun went down and then slept in two phases known as “biphasic sleep.”

He pointed out that throughout history, there are numerous accounts of what scholars call "biphasic sleep."

Prior to biphasic sleep, some historians believe that hunter-gatherer societies slept in one smaller stretch throughout the night — closer to how we do now.

"It took place over the course of the 19th century, and there were still remote rural areas in the early 20th century in which the inhabitants exhibited biphasic sleep."