A primitive tribe was observed. Researchers saw that various members of a group slept at different times in order to provide a lookout. Called the “sentinel hypothesis”, it also suggested that one reason grandparents lived so long was to keep grandchildren alive.
Youngsters are night owls and the elders rise early and need less sleep. As a result, it’s important to have people of all ages in any population.
While evaluating the tribe, all members were asleep at the same time for only 18 minutes. This follows the animal model where groups of social creatures like the meerkat, always have someone on the lookout while everyone else sleeps.
We humans have been doing this for hundreds of thousands of years starting when we were sleeping in the bush and exposed to predators and rival groups of humans. Explains a lot, doesn’t it?
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