A circadian rhythm occurs once every 24 hours. For example, the sleep/wake cycle and cycle of body temperature.
Mammals synchronise their CRs to the environment.
Aschoff and Wever (1962).
Ps were placed in an underground WW2 bunker in the absence of environmental time cues for 3 to 4 weeks. They all settled into a sleep/wake cycle of 25 hours.
Spent 2 months (61 days) in caves. He surfaced on the 17th September, thinking it was the 20th August.
In 1972, He spent 205…