Rewrite the Headlines: Can societies without electricity reveal how our ancestors slept?

Over the first few weeks of February, we’re showcasing the top entries in both the school and undergraduate categories of our Rewrite the Headlines competition (full list of winners here). We continue with another of our commended undergraduate entries, from Hannah Miller at the University of Glasgow.

Can societies without electricity reveal how our ancestors slept?

With insomnia currently being the most common sleep disorder, many think that advances in technology are disturbing our sleep. However, with the research of sleep only being a relatively new field, we can’t compare today’s sleep habits with the past.

Researchers from the USA have attempted to gain a picture of how our ancestors would have slept. A group headed up by Jerome Siegel (head of a UCLA lab researching the sleep evolution and disorders) examined the sleep of 94 people from 3 different pre-industrial societies: The Hadza in Northern Tanzania, the San in Namibia, and the Tsimane in Bolivia. The article was published in the peer-reviewed journal ‘Current Biology’. They measured activity and light with sensors attached to the wrist, in both summer and winter. They also measured the temperature of the Sans’ bodies, finger and sleeping locations for the first four days. These measurements allowed the researchers to work out the groups’ resting times, and changes in their environments.

The researchers found similar patterns across societies, with sleep times between 5.7 and 7.1 hours. Sleep usually started a few hours after sunset, whereas waking was closer to sunrise – similar to people in industrialised societies. The only exception was the San in summer, who generally went to bed very late and slept until one hour after sunrise. One point of difference was that all groups tended to sleep an hour more during winter periods, which contrasts with the lack of marked seasonal differences in industrialised societies. When light and temperature changes were compared, sleep was more related to temperature changes (with temperature dips being strongly linked to waking). The authors suggested temperature could be related to the different sleeping patterns seen in the Namibian group during summer time. Specifically, they suggest that the lower morning temperatures in the Namibian summer were linked to later waking.

The group also tried to gauge whether any of the Tsimane or San suffered from insomnia. As there is no specific word for this in the languages of these societies, they had to describe the problem in terms of trouble getting to/staying asleep. Although some participants had experienced some of the symptoms, the rates were much lower than in industrial societies.

There are some issues which could have limited the accuracy of the results, or the implications taken from them. Practically speaking, the research incorporates a fair number of individuals, given the difficulties associated with reaching remote people groups. Yet the research could be limited by the location of the people studied, since the groups were all from fairly tropical climates – many ‘industrialised’ populations reside in more extreme latitudes, which means that these findings may only show how ancestors slept in similar climates. The combination of better adult health in the pre-industrial societies, with potentially biasing uneven group sizes, also limit the application of the results to industrialised societies. Another limitation is that some of the points raised in the research do not seem to be based on evidence. The researchers refer to speculations (such as the idea that post-lunch energy dips point towards an innate midday nap), without referencing a source. This limits the strength of the counter-argument apparently presented by the results in question.

A press release posted by UCLA largely presents the findings as a challenge to the belief that modern sleeping patterns have reduced the quantity of sleep we get. However, they don’t account for the assumptions being made when modern hunter-gatherer societies are compared to our ancient ancestors. The findings are more an indication of ancestral sleeping, rather than evidence. Another criticism is that the press release also suggests the research informs us about innate napping, despite the lack of evidence provided for this idea. A stronger point raised by the press release is that their findings rule out the suggestion that technology is the sole cause of late bedtimes. This point is well made, given that Siegel still points out that technology could play some role without being the only cause. Similarly, Siegel carefully applies the link found between sleep and temperature to the treatment of sleep disorders. Without overstating their findings, he suggests ‘it may well be that falling environmental temperature is integral to sleep control in humans’.

The study was reported in the Guardian, with a good explanation of the background and a clear description of the basics of the process. The reporting included mention of the authors and the location of publication, as well as a link to the abstract. They can also be commended on including an expert opinion, although fail to comment on the disagreement between his statement and the findings of the study. The expert was Professor Derk-Jan Dijk of the Surrey Sleep Research Centre, who states that technology has impacted our sleep patterns. Much of his quotation is also more concerned with sleep problems, than with the general sleeping patterns examined in the study. A more serious criticism of the article is that they state that ‘modern life has done nothing to rob us of sleep’ in a picture caption, when the research does not disprove that our lifestyle could interrupt our sleeping patterns. Generally, the media article tends to mirror the press release, but places more of an emphasis on the potential medical implications than the actual findings.

Overall, the media report and the press release are accurate in their description of how the research was carried out, but as is often the case, seem to read a little too much into the results. In particular, the Guardian article does well to explain clearly how the the research was carried out, and puts the implications into simple language. However, strong conclusions are suggested when the findings are possibly not quite as applicable as the researchers would hope. While the research can be praised for its novel approach to studying sleep in pre-industrial societies, it still seems a far leap to suggest that this is evidence of how our ancestors slept.

Hannah Miller, University of Glasgow

References:

Research paper – Yetish, G., Kaplan, H., Gurven, M., Wood, B., Pontzer, H., Manger, P. R., … & Siegel, J. M. (2015). Natural sleep and its seasonal variations in three pre-industrial societies. Current Biology, 25(21), 2862-2868. http://www.sciencedirect.com/science/article/pii/S0960982215011574

Press release – Sullivan, M. (2015). Our ancestors probably didn’t get 8 hours a night, either. Retrieved December 28^th, 2015, from http://newsroom.ucla.edu/releases/our-ancestors-probably-didnt-get-8-hours-a-night-either

Guardian article – Sample, I. (2015). Modern life is rubbish? Sleep is just the same as ever, say scientists. Retieved December 28^th, 2015, from http://www.theguardian.com/science/2015/oct/15/modern-life-is-rubbish-sleep-is-just-the-same-as-ever-say-scientists

The Rewrite the Headlines competition was supported by funding from the British Academy, with additional funding from the University of Strathclyde.

Prizes were supported by the British Academy, the University of Strathclyde, the School of Chemistry at the University of St. Andrews, the School of Social Work and Social Policy at the University of Strathclyde, the University of Dundee School of Life Sciences, and the Particle Physics Experiment Research Group at the University of Edinburgh, the Social Research Association, the Scottish History Society, and Palgrave Macmillan.

Competition details can be accessed at https://researchtheheadlines.org/rewritetheheadlines, and the full list of winners is available here.