Abstract
Did artificial light reshape human sleep/wake cycle? Most likely the answer is yes. Did artificial light misalign the sleep/wake cycle in industrialized societies relative to the natural cycle of light and dark? For the average person —that is, obviating the tail of the distributions— the answer is probably not.
Sleep timing in industrial (data from eight national time use surveys) and pre-industrial, hunter-gatherer/horticulturalist societies (seven data from three previous reports) with and without access to artificial light finds a remarkable accommodation across a wide range of angular distance to Equator (0° to 55°) in trends dominated by the extreme light/dark conditions.
Winter sunrise time —the latest sunrise year round— triggers sleep offset, which delays in the poleward direction. The same trend is observed in bedtimes, dictated by the previous sleep offset, a circadian, homeostatic response. That way two of the most significant human sleep/wake features, the abhorrence for waking before sunrise and the abhorrence for going to bed before sunset, meet in a common natural event. None of them are related to artificial light.
Footnotes
↵∗ olalla{at}us.es; Twitter: @MartinOlalla_JM