Sleep duration in hunter-gatherer societies is similar to or less than in modern industrialized cultures, averaging between 5.9-7.1 hours per night. Sleep onset typically occurs several hours after sunset, rather than at sunset. Maximum daily light exposure is in the morning, not at noon. Sleep occurs during the coolest part of the night, and people awaken near the temperature minimum, unlike most modern cultures where people awaken as temperatures rise. Overall, hunter-gatherers exhibit sleep patterns and durations similar to our evolutionary past before the influence of electricity and modern lifestyles.

1. Sleep Myths and
Realities:
Lessons from
Hunter-Gatherers
B·DEBATE
International Center for
Scientific Debate
Barcelona,
October 18, 2018
Jerry Siegel
Center for Sleep Research
UCLA Psychiatry
Los Angeles

2. •But the tools to measure sleep were not developed until after the
invention of the electric light and other aspects of modern culture.
•What is human sleep like in the “pre-industrial” environment?

3. • Three groups studied:
• First group, the Hadza
• Live near Olduvai Gorge by
Lake Eyasi.
• No electricity (no internet,
TV or electric light)
• No guns
• No coffee/energy drinks
• No agriculture
• Non-pastoral – no cattle,
pigs, chickens dogs or cats
• Nomadic (no permanent
structures)

4. • They have “no obesity,” but
do not have a higher daily
energy expenditure
(kCal/day) than Americans
despite large differences in
activity level (Pontzer et al,
2012)
• Hadza sleep on animal
skins, under the stars

5. Second group: San (Bushmen, !Kung, Ju/'hoansi) hunter-
gatherers of Namibia: most diverse human genome
Voyager 1: San hunting oryx

6. Third group: Tsimane People, Forager-
horticulturalists, San Borja, Bolivia

7. Recording sites
Study of 3 groups facilitates detection of common
aspects of human sleep in “natural” conditions

8. Actiwatch on left (non-dominant)
hand
Event marker
Light sensor. 5-100,000
lux (log display)

9. On wrist
sh/moon-phases/lunar-calendar-2013/05/22/
com/worldclock/astronomy.html?n=71&month=5&year=2013&obj=moon&afl=-11&day=1
Yellow-light level
Black-mvts/epoch
Dark blue-sleep
Light blue-rest
6 days

11. Actiwatch records from three groups
94 adults recorded, for a total of 1,165 days

12. Sleep duration is nearly one hour
longer in winter than in summer in
both groups examined across seasons

13. Similar sleep
duration in all 3
groups:
5.9-7.1h
Sleep period
(duration +
W.A.S.O.):
6.9-8.5h
wake after sleep
onset:
similar or lower
than average
‘modern’ controls
GROUP/
START DATE
NIGHT
DURATION
SLEEP
DURATION
SLEEP PERIOD
(SLEEP TIME +
WASO)
HADZA 12.1 6.3 7.7
TSIMANE
8/18/13 WINTER 12.4 6.6 8.0
9/1/13 12.2 6.4 8.0
10/3/13 11.7 6.4 7.5
10/18/13 11.5 6.5 7.5
10/29/13 11.4 5.9 7.2
11/28/13 SPRING- SUMMER 11.1 5.7 6.9
SAN
5/14 FALL WINTER 12.9 7.1 8.3
8/11 12.6 6.9 8.5
1/15 SUMMER 11.0 6.2 7.4
AVERAGE 6.4 7.7

14. Health of non-industrial
populations
Extensive health studies of the Tsimané have found that
although child mortality is higher than in “modern” societies,
largely due to infectious diseases and lack of immunization,
adults have much lower levels of hypertension and
atherosclerosis (Kaplan, 2017), lower levels of Alzheimer’s
and higher levels of physical fitness than industrial
populations. Obesity rates are <3%. Many live into their 60s,
70s, 80s and beyond. Similar health findings have been
reported in the Hadza and San.
We sampled subjects between 20 and 55, average age 37.

15. L10 test light levels observatory 12.xls
Solar noon

16. • Maximum light
exposure is at ~9AM
(solar), NOT at noon.
This is the case in both
summer and winter, at
equator and away from
equator. Possible
relation to depression.
• Activity after sunset, no
evidence for period of
nighttime activity.
• No regular decrease of
activity at noon.
• Winter naps on <7% of
days, Summer on <22%
of days, in San (690
days of observation).

18. Outside British Museum July 5, 2017

19. • Sleep onset occurs several hours after sunset (3.3 hours on
average). The time of sleep onset is very variable.
• Wake onset occurs before or shortly after sunrise. The time
of wake onset is much less variable than the time of sleep
onset.
Timing of sleep onset and offset relative to sunrise and sunset

20. iButtons for
temperature
recording in the
San
Timing of Hadza sleep in relation to light and Serengeti temperature:
Sleep onset 3.4-h after sunset, sleep offset 1-h before sunrise.
Is environmental temperature linked to sleep timing?
53º-84º F

21. • Sleep occurs during fall
in ambient temperature
• Awakening at
temperature nadir, not
sunrise
• Vasoconstriction
coincident with
awakening unlike
industrial populations
• Daily temperature
rhythm reduced or
eliminated in “modern”
cultures

22. Non-industrial people
• 7 or 28 day recordings, 94 subjects, 1,165 days of
recordings
• All 3 groups have similar sleep parameters
• No sleep onset at sunset, even in the absence of
electric light
• Sleep duration in non-industrial societies is the
same as, or less than, that of industrial cultures
• Little napping in winter, low level (22%) in summer
• No consistent interruption of nighttime sleep
• One hour difference between summer and winter
sleep duration

23. • Maximal light exposure occurs in morning
• Sleeping period occupies the coldest portion of
the night. Sleep occurs during a period of
temperature decrease
• Awakening occurs near temperature nadir,
accompanied by peripheral vasoconstriction (no
vasodilation at sleep onset) - the reverse of the
“modern” pattern
• Temperature is a major regulator of sleep under
“pre-modern” conditions
• Little or no insomnia (<2% vs. > 10-20% in US)
Non-industrial people

24. "The subject of sleeplessness is once more
under public discussion. The hurry and
excitement of modern life is quite correctly
held to be responsible for much of the
insomnia of which we hear: and most of the
articles and letters are full of good advice to
live more quietly and of platitudes
concerning the harmfulness of rush and
worry.
British Medical Journal, 1894

27. Marmoset, Tamarin
12.6 and 13.3h sleep/24
Little W in dark, sleep and W in light
(Kantha 2006)

28. Juvenile Rhesus
(Macaca mulatta)
10 h sleep/24 (Barrett et al, 2009)

29. Chimpanzee (Pan troglodytes)
10 h sleep/24h nap in midday,
little W at night
Adey, 1972
Diurnal primates DO go to sleep at lights off, unlike
hunter-gatherers and “modern” humans.

30. Human retina has highest rod % (lowest
cone %) of any diurnal primate
Wikler et al., 1990, Roelof Hut et al., 2012 and 2017 (in press)
i.e. we have evolved to see better after sunset than
any other primate whose retina has been studied
* Primates with 24 h sleep studies
species latin name % cones % rods
ground squirrel Spermophilus citellus 97.0 3.0
*marmoset Callithrix jacchus) 24.3 75.7
squirrel monkey Saimiri sciureus 9.3 90.7
capuchin Cebus apella 7.9 92.1
*macaque Macaca fascicularis 6.1 93.9
*human Homo sapiens 4.7 95.3
rat Rattus norvegicus 1.0 99.0
Primates

31. Humans appear to be unique among diurnal
primates in having an extended period of
waking after sunset. This is seen in hunter-
gatherers, as well as in “modern” populations.
Staying up late is part of what makes us human,
as is improved night vision.
Waking time after sunset provides additional time for adaptive
activities that do not occur in other diurnal primates:
•Small fires are used to cook food. This increases the calories their food
conveys and offsets the energy savings that would have occurred if they
were asleep.
•Preparing poison arrows, repairing hunting and other equipment
•Social bonding and information exchange using language

34. Kripke, 2003
Lifespan does not increase with sleep time. There is an
optimal amount of sleep of 7-8 h in the U.S.

35. Sleep heart health study, PGR,
6441 subjects >40

36. A total of 113,138 participants (68,548 women and 44,590 men) of the
Shanghai Women’s and Men’s Health Studies, aged 44–79 y and 40–75 y.
Cai et al., 2015. Preexisting conditions controlled for.

37. SLEEP AND COGNITIVE PERFORMANCE FROM TEENS TO OLD
AGE: MORE IS NOT BETTER (Sleep, 2016)
Subtitle: More sleep is not better for cognitive performance
Anne Richards, MD MPH; Sabra S. Inslicht, PhD; Thomas Metzler, MS;
Brian Mohlenhoff, MD; Madhu Rao, MD; Aoife O’Donovan, PhD;
Thomas C. Neylan, MD; University of California, San Francisco; San
Francisco VA Medical Center; Palo Alto VA Medical Center

38. N=512,823:
Self reported sleep
duration.

39. Relationship of Mean Adjusted Log Score and Self-Reported Habitual
Sleep Duration by Age Category for Speed Match, Memory Matrix, and
Raindrops

40. Relationship of Mean Adjusted Log Score and Self-Reported Habitual
Sleep Duration for 15-19 year olds and 20-24 year olds for Speed Match,
Memory Matrix, and Raindrops

41. • 7-8 hours of sleep is optimal for
survival.
• More sleep is not necessarily better
for performance.
• But there is little evidence on the
effects of changes (increases or
decreases) in spontaneous sleep
duration.
www.semel.ucla.edu/sleepresearch