Dr Neil Stanley Independent Sleep Expert
There are 7 major problems for the hypothesis that, to quote Ekirch, “Until the close of the early modern era, Western Europeans on most evenings experienced two major intervals of sleep bridged by up to an hour or more of quiet wakefulness“ and that this mode of sleeping was “the predominant pattern of sleep before the Industrial Revolution”:- 1. The absence of descriptions in the literature of behaviour actually resembling Ekirch’s proposed ‘segmented sleep’ 2. The scarcity of the phrase ‘second sleep’ and its absence in almost all other languages in which the phrase ‘first sleep’ occurs. 3. The absence of descriptions, or names in any language, of the hypothesised intervening period of wakefulness. 4. The existence in a number of cultures of ‘third sleep’ 5. The fact that the vast majority of examples of ‘first sleep’ relate to people being ‘in’ or ‘awakened from’ their ‘first sleep’ not awaking after their ‘first sleep’ as Ekirch contends. 6. The fact that examples of ‘first sleep’ occur at various times of the night and even during the day. 7. The lack of any scientific evidence of ‘segmented sleep’ in people living under real-life ‘pre-industrial’ conditions. Ekirch states by way of explanation for the sleep patterns seen in the non-western societies states that “What, of course, all these cultures shared with early societies in Europe and America......was a severe shortage of artificial illumination”. Whilst there is an increasing body of evidence that artificial light undoubtedly has had an influence in shaping the pattern of modern sleep, three recent studies, which were available when Ekirch wrote is letter to Sleep, have shown that artificial light cannot be the only explanation for ‘post-industrial’ sleep. de la Iglesia et al (2015) studied two communities of indigenous Toba/Qom in the Argentinean Chaco. The two communities share the same ethnic and sociocultural background, but one has free access to electricity while the other relies exclusively on natural light. Their study found that, participants with access to electricity had a shorter daily sleep bout in both summer (43 ± 21 min) and winter (56 ± 17 min) than those living under natural light conditions. They found whilst the two communities woke up and got up at similar times during both seasons the difference was due to later daily bedtime and sleep onset in the community with electricity. Fragmentation of sleep in both communities was similar. The length of the natural night during summer was 10.5hrs and in winter 12.9hrs but in the community without access to electric light had a consolidated sleep period averaging 7 h in summer and approx. 8.5 h in winter. (both well within the average ‘western’ sleep duration)  This demonstrates that even though this community lack access to artificial illumination they were able to sleep for a period significantly less than the length of the night. Access to electricity only led to an approx.1hr reduction in the duration of sleep. In discussing their results in the terms of Ekirch’s paper they state that their results “do not show evidence of fragmented sleep or a bout of quiet wakefulness in either community”. Piosczyk et al. (2014) also did not observe ‘segmented sleep’ or sleep fragmentation in his study of volunteers living under Stone Age conditions with a night length of approx. 11hrs. From these studies it can be seen that whilst artificial light can to a degree affect the boundaries of sleep it cannot not account for the lack of fragmentation of sleep seen in ‘modern’ western sleep. Wright et al (2013) concluded that “reduced exposure to sunlight and the widespread use of electrical lighting in the constructed environment has altered human circadian physiology leading to a major change in the timing of our sleep and wakefulness.” However they fond no evidence of ‘segmented sleep’ in their subjects. Wright KP, McHill AW, Birks BR, Griffin BR, Rusterholz T, Chinoy ED. Entrainment of the human circadian clock to the natural light-dark cycle. Current Biology. 2013 Aug 19;23(16):1554-8. here  Piosczyk H, Landmann N, Holz J, Feige B, Riemann D, Nissen C, Voderholzer U. Prolonged sleep under Stone Age conditions. J Clin Sleep Med. 2014 Jul 15;10(7):719-22. here  de la Iglesia HO, Fernández-Duque E, Golombek DA, Lanza N, Duffy JF, Czeisler CA, Valeggia CR. Access to Electric light is associated with shorter sleep duration in a traditionally hunter-gatherer community. Journal of biological rhythms. 2015 342-350 here Yetish G, Kaplan H, Gurven M, Wood B, Pontzer H, Manger PR, Wilson C, McGregor R, Siegel JM. Natural sleep and its seasonal variations in three pre-industrial societies. Current Biology. 2015 25(21):2862-8.here 
© Dr. Neil Stanley 2013-2019