Michael Siffre

Michael Siffre was a British physiologist known for his research on human biological rhythms, specifically the sleep-wake cycle, or circadian rhythm. In his experiments, he isolated himself in caves and underground environments without external cues like light or clocks to study natural body rhythms. His work demonstrated that humans have an internal clock—roughly a 24-hour cycle—that regulates sleep, wakefulness, and other bodily functions, independent of the environment. Siffre’s studies helped deepen understanding of how our internal clocks work and their importance for health and daily functioning.