iirc, biphasic sleep is the “usual way” people sleep without the advent of electricity, yes? “the waking hour”, and all that.

I wonder if there was an increase in dementia-related disorders once lightbulbs kept people up longer.

> iirc, biphasic sleep is the “usual way” people sleep without the advent of electricity, yes? “the waking hour”, and all that.

I honestly believe that this is not "natural", but rather an adaptation to the absurdly long European winter nights. Note that we didn't evolve there, so it seems unlikely that bi-phasic sleep is the most primal way.