ORIGINAL RESEARCH ARTICLE Segmented sleep in a nonelectric, small-scale agricultural society in Madagascar David R. Samson 1 | Melissa B. Manus 2 | Andrew D. Krystal 3 | Efe Fakir 4 | James J. Yu 1 | Charles L. Nunn 1,2 1 Department of Evolutionary Anthropology, Duke University, Durham, North Carolina 27708 2 Duke Global Health Institute, Duke University, Durham, North Carolina 27708 3 Psychiatry and Behavioral Sciences, Duke University, Durham, North Carolina 27708 4 Bahcesehir University, School of Medicine, Istanbul, Turkey Correspondence David R. Samson, Biological Sciences 107, Duke University, Durham, NC 27708, USA. Email: david.samson@duke.edu Funding information Duke University and BASS Connections Abstract Objectives: We studied sleep in a rural population in Madagascar to (i) characterize sleep in an equatorial small-scale agricultural population without electricity, (ii) assess whether sleep is linked to noise levels in a dense population, and (iii) examine the effects of experimentally introduced artificial light on sleep timing. Methods: Using actigraphy, sleep–wake patterns were analyzed for both daytime napping and nighttime wakefulness in 21 participants for a sum total of 292 days. Functional linear modeling was used to characterize 24-h time-averaged circadian patterns and to investigate the effect of experimentally introduced mobile field lights on sleep timing. We also obtained the first polysomnography (PSG) recordings of sleep in a traditional population. Results: In every measure of sleep duration and quality, the Malagasy population experienced shorter and lower quality sleep when compared to similarly measured postindustrial values. The population slept for a total of 6.5 h per night and napped during 89% of recorded days. We observed a peak in activity after midnight for both sexes on 49% of nights, consistent with segmented sleep. Access to mobile field lights had no statistical effect on nighttime sleep timing. From PSG, we documented relatively short rapid eye movement (14%), poor sleep efficiency (66%), and high wake after sleep onset (162 min). Conclusions: Sleep in this population is segmented, similar to the “first” sleep and “second” sleep reported in the historical record. Moreover, although average sleep duration and quality were lower than documented in Western populations, circadian rhythms were more stable across days. 1 | INTRODUCTION Our understanding of sleep mechanisms, physiology, and chronobiology has burgeoned over the past 50 years (Campbell & Tobler, 1984; Carskadon & Dement, 2005; Heller, 2005; Mistlberger & Rusak, 2005; Zepelin, Siegel, & Tobler, 2005). However, the sample from which researchers have generated human data has primarily drawn from postin- dustrial populations from the United States, Europe, and Japan (Knutson, 2014). In contrast, remarkably little is known about the sleep of traditional populations that experi- ence natural lighting (henceforth, nonelectric populations). These populations practice largely subsistence patterns including foraging, small-scale agriculture, horticultural, and pastoralist strategies, and their lives are more closely linked to natural daily and seasonal rhythms. The cross-cultural study of sleep architecture, sleep quality, sleep–wake phas- ing, and circadian rhythms is thus in its infancy (McKenna, Ball, & Gettler, 2007; Worthman, 2008; Worthman & Melby, 2002). Recent advances in understanding sleep in nonelectric populations arise from increasing adoption of actigraphy, a Am J Hum Biol. 2017;e22979. https://doi.org/10.1002/ajhb.22979 wileyonlinelibrary.com/journal/ajhb V C 2017 Wiley Periodicals, Inc. | 1 of 13 Received: 12 July 2016 | Revised: 25 October 2016 | Accepted: 16 January 2017 DOI 10.1002/ajhb.22979 American Journal of Human Biology