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> I'm sort of joking, but not quite. I can't think of an objective reason why being a 'night owl' is biologically an abnormality/deficiency.

It leads to being awake during dark hours, and humans do not have night vision.

Also Advanced Sleep Phase Disorder, while less common, is also a thing and also leads to being awake during dark hours.

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> It leads to being awake during dark hours, and humans do not have night vision.

Humans most definitely can see at night. Not as well as other animals, but we can do it. People also tend to actually stay awake in the dark, otherwise our sleeping times would vary quite a bit throughout the year - by this logic, if you live further up North you would have to sleep (almost) continuously throughout the winter.

A reminder that we did not evolve "up North".

Also, we can barely see at night, and that's probably why we sleep when we do, for as long as we do. To keep us safe.

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