There is no single universally accepted theory of why some people are night owls, but evolutionary biologists think that communities with more variation in chronotypes may have been more likely to survive, The Guardian reports.

If not everyone needs to sleep at the same time, then some members of the tribe can stand guard and protect those who are resting. A recent study of a modern-day hunter-gatherer tribe found that during a three-week period, there were only 18 minutes during which all of the 33 tribe members were asleep simultaneously.

Another theory is that variation is simply how genetics works. Colin Espie, professor of sleep medicine at the University of Oxford, says this mirrors differences in hair, eye and skin color, or height. “It’s a bit like any other biological characteristic. There’s a normal distribution, so there are people on both extremes – and the majority of people are neither.”

Natural night owlsare fundamentally different to insomniacs or people who stay up until the early hours because of family or work circumstances. Being a night owl isn’t a problem – unless you’re trying to fit into a schedule that doesn’t suit your natural cycle.

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