[corty]

I would guess that biphasic sleep was killed by the common consumption of stimulant drugs like tea or coffee in western culture.

[ashtonkem]

Depends which kind of biphasic you’re talking about.

Afternoon naps were probably killed by stimulants. But the “first” and “second” sleep historically common were probably killed off by the electric light.

[abeppu]

That's an interesting guess -- I had read that biphasic sleep was common in the West prior to the industrial revolution, when work for long days away from home was common, and light began to be more available at night.

Maybe the right kind of historian is around to answer: Was biphasic sleep also the norm in preindustral societies that had tea or coffee cultures relatively early?

[taeric]

I would guess electric lights.

[corty]

That doesn't make sense to me, siesta wastes precious daylight. If anything, the availability of light at night should have promoted daytime sleep, if there was any influence.

[nijaru]

Growing up somewhere with a Mediterranean climate that has hot summers, I’ve always assumed it was to sleep through the heat before a/c was invented.

[taeric]

There is almost certainly something to this. Sun exposure is dangerous.

[nradov]

How can people sleep during the hottest part of the day? I've never been able to manage that.

[eru]

You can doze off. And falling asleep is a skill you can train.

(I can nap in hotter and brighter conditions during the day than I can tolerate at night.)

[taeric]

Lights help extend the evening. Such that you sort of barrel through a time that would make you tired by just cranking up the light.