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I read about this years ago.
First, there were lights. Even cavemen kept a fire going all night to ward off predators. Then candles and torches. People have always had artificial light, but it was fire which has a much warmer wavelength than sunlight and does not disrupt sleep because your body does not think it is daylight.
People always lived in groups, including in cavemen times. It is supposed this is why some people are "night owls" and some are "morning people" - the natural distribution of when you sleep varies among people and it is thought this is so there are always some people in the group awake at any given time to keep watch for predators.
Second, there is plenty you can do with even minimal or no light. Men and women have sex. Women nurse infants. People groom each other, combing hair, removing lice. People talk and plan. If you have some light from fire you can work on making or repairing tools and clothing or prepare food which has a long preparation time or work on preserving food such as by butchering a large animal and salting the meat. You can wash clothes if you prepared by having a bucket of water ready. You can cook and eat. If you live in buildings you can do maintenance work on the interior of the home. In some cultures people might pray, or meditate/think, or sneak out to commit crimes in the dark, or meet a lover for sex away from other people. Remember most people in history until very recently could not read, and books were not easily available, so it's not like they would be reading anyway even if there was plenty of light.
Even with just starlight you can certainly do things like have sex or nurse infants or talk.
Most of all, remember most of the year there are 10 hours of darkness or significantly more depending on latitude. Near the equator where we evolved, there are almost always 12 hours of darkness every day. If you sleep 7 or 8 hours you are going to be awake for 4-5 hours of darkness no matter what. It's not particularly radical to suggest this was in the middle of the night rather than the early part of the night (going to bed late) or the very late hours before dawn (getting up very early). Either way you are awake in the dark for a good 4 hours or more. So the question remains "what do you do in the dark" regardless of whether it's biphasic sleep or not. And people always found things to do.
First, there were lights. Even cavemen kept a fire going all night to ward off predators. Then candles and torches. People have always had artificial light, but it was fire which has a much warmer wavelength than sunlight and does not disrupt sleep because your body does not think it is daylight.
People always lived in groups, including in cavemen times. It is supposed this is why some people are "night owls" and some are "morning people" - the natural distribution of when you sleep varies among people and it is thought this is so there are always some people in the group awake at any given time to keep watch for predators.
Second, there is plenty you can do with even minimal or no light. Men and women have sex. Women nurse infants. People groom each other, combing hair, removing lice. People talk and plan. If you have some light from fire you can work on making or repairing tools and clothing or prepare food which has a long preparation time or work on preserving food such as by butchering a large animal and salting the meat. You can wash clothes if you prepared by having a bucket of water ready. You can cook and eat. If you live in buildings you can do maintenance work on the interior of the home. In some cultures people might pray, or meditate/think, or sneak out to commit crimes in the dark, or meet a lover for sex away from other people. Remember most people in history until very recently could not read, and books were not easily available, so it's not like they would be reading anyway even if there was plenty of light.
Even with just starlight you can certainly do things like have sex or nurse infants or talk.
Most of all, remember most of the year there are 10 hours of darkness or significantly more depending on latitude. Near the equator where we evolved, there are almost always 12 hours of darkness every day. If you sleep 7 or 8 hours you are going to be awake for 4-5 hours of darkness no matter what. It's not particularly radical to suggest this was in the middle of the night rather than the early part of the night (going to bed late) or the very late hours before dawn (getting up very early). Either way you are awake in the dark for a good 4 hours or more. So the question remains "what do you do in the dark" regardless of whether it's biphasic sleep or not. And people always found things to do.
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