When do most people wake up?

Biphasic sleep Sleeping through the night is a modern invention

When nobles, large farmers or plantation owners complained about the lack of work ethic of their workers, the sources often suspected the bad character of the lower folk, says Ekirch. "Totally wrong. The problem was that they did not get enough good sleep. I am convinced that large parts of the early modern population, especially workers, were chronically sleep deprived."

Artificial lighting ended biphasic sleep

With the sudden growth of artificial lighting, people's sleep behavior changed dramatically. As a result of industrialization, candles first became much more available and gas lanterns lit the streets outside. The invention of the electric light bulb finally gave artificial light its complete breakthrough. Now the time in the dark can also be used productively.

Instead of going to bed at nine or ten o'clock, families in urban areas in particular stay up until eleven or midnight. However, you still have to get up at six in the morning. So they sleep less and get more and more tired as the day progresses until they go back to bed late. Therefore, you can now sleep through the night. By the end of the 19th century, the second sleep had practically disappeared.

Professor Roger Ekirch, historian

Biphasic sleep has been shown in experiments

Unfortunately, there is little evidence as to whether there was biphasic sleep in other regions of the world, says Ekirch. Some travel reports would have mentioned biphasic sleep in Cylon, now Sri Lanka. There are also reports of this kind for the indigenous people of Australia. Some peoples in Africa and South America are said to have slept through the night.

However, there are still relatively young, experimental studies that show that people develop a biphasic sleep pattern again under certain conditions. For example, Thomas Wehr's team at the US National Institute for Mental Health reduced the lighting time for test subjects to a maximum of ten hours a day. After about three weeks, her sleep became biphasic.