Sleep/wake synchronization across latitude

Analysis of time use surveys in seventeen European countries and two American countries suggest that the winter sunrise —the latest sunrise year round— is a synchronizer for the sleep/wake cycle in standard population below 54° latitude, in competition with the noon synchronizer. When comparing industrialized data to data from hunter/gatherer, pre-industrial, Tropical societies only the late event survives as a synchronizer below 54° latitude. People rise immediately before sunrise —winter sunrise in industrialized mid-latitude societies— and abhor morning darkness. Synchronization propagates through the sleep/wake cycle so that people go to bed with increasing distance to sunset in winter as latitude increases in a scenario dominated by artificial light. This suggests a leading role of the homeostatic sleep pressure in understanding sleep/wake cycle at social level. WARNING This pre-print has been largely upgraded and restyled in “Sleep timing in industrial and pre-industrial societies sync to the light/dark cycle” ( https://doi.org/10.1101/392035 ). In this new pre-print data coming from the Harmonsized European Time Use Surveys (HETUS) and referred to the “sleep/wake and other personal care” cycle were not analyzed. Instead two new pre-industrial data are included. Therefore this old pre-print you are about to read remains as a source for these data (see Figure 3 and Table III, Table VII to IX) and a source of information in the range of latitude above 54°.