Story perspectives

1960s Study Reveals Human Body's 48-Hour Internal Clock

1/4/2026

Summary

Story summary

In the 1960s, French geologist Michel Siffre showed the human body has an internal clock independent of the 24-hour day.
In the Scarasson cave, his sleep-wake cycles stretched to about 48 hours, challenging scientific understanding.
This work laid the foundation for human chronobiology and influenced research on space missions and medical treatments.
Today, Siffre's findings inform studies of circadian rhythms and resilience in extreme environments.

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Story summary

In the 1960s, French geologist Michel Siffre showed the human body has an internal clock independent of the 24-hour day.
In the Scarasson cave, his sleep-wake cycles stretched to about 48 hours, challenging scientific understanding.
This work laid the foundation for human chronobiology and influenced research on space missions and medical treatments.
Today, Siffre's findings inform studies of circadian rhythms and resilience in extreme environments.