The term “polyphasic sleep” dates to early 20th-century observations of animal activity (J. S. Szymanski). In pre-industrial societies, segmented “first” and “second” sleep with a wake interval was common; industrialization and electric light favored consolidated monophasic sleep. Infants and many animals are naturally polyphasic.

Biphasic/segmented patterns were common in early modern Europe (night split with a wake period for prayer/reading/reflection). Siesta cultures (Mediterranean, Latin America, parts of Africa/Asia) combine a long night sleep with an early-afternoon nap, matching circadian and environmental factors (e.g., heat).

Historical records and darkness-condition studies (e.g., Wehr) indicate humans can revert to multi-phase patterns. However, contemporary studies of some hunter-gatherer groups suggest consolidated nighttime sleep may be typical in equatorial regions, questioning the universality of adult polyphasic sleep.