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Letter: Splitting sleep in two was once a thing

Published 20 August 2025

From Larry Stoter, The Narth, Monmouthshire, UK

When it comes to body clocks, researchers should investigate the phenomenon of “second sleep”, or biphasic sleep. This is fairly well-known historically and among some anthropologists. It seems to have been relatively common and widespread at a time when people’s daily rhythms were largely determined by the sun and when bright indoor lighting was unavailable for most people(2 August, p 30).

Typically, people would go to sleep perhaps 2 hours after sunset, sleep for a few hours, wake for a period, then sleep again until early morning.

Perhaps a more relaxed attitude to sleep and a return to biphasic sleeping would lessen the incidence of sleep disorders.

Issue no. 3557 published 23 August 2025

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