Humans May Be Naturally Cathemeral, Not Strictly Diurnal, New Study Suggests

Recent research examining the lifestyles of hunter‑gatherer societies indicates that humans are not strictly diurnal. Instead, they exhibit a cathemeral pattern, with intermittent periods of activity during the night. This finding aligns human sleep behavior with that of certain lemur species, which also show flexible, multi‑phase activity cycles. The evidence challenges the long‑held view that humans are primarily daytime active and suggests that our ancestors’ circadian rhythms were more adaptable to environmental conditions. Understanding this natural flexibility could reshape how we think about modern sleep disorders and the evolutionary roots of human circadian biology.