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2015-10-16 05:50:14
By Rebecca Morelle Science Correspondent, BBC News
16 October 2015
Our ancestors may have got less sleep than we do, a study suggests.
US researchers studied the sleeping patterns of traditional societies in Africa
and South America, whose lifestyles closely resemble ancient hunter gatherers.
They monitored 98 people for 1,165 nights, and found that they slept for an
average of 6.5 hours per night.
By comparison, the scientists said that most people in the US get about seven
hours, according to a large sleep poll.
The new study, published in the journal Current Biology, also finds that
temperature played a greater role than light in shaping sleeping patterns.
Prof Jerome Siegel, from the University of California, Los Angeles, said: "The
issue is: what is the data on how sleep has changed?
"And it occurred to me that these groups, which are rapidly disappearing, give
the last opportunity to really know what human sleep was like before we all
created our various civilisations.
"What is absolutely clear is that they don't sleep more than we do."
No naps
From artificial lights, to late night TV, and now the ever-present glow of our
smart phones, modern life is often blamed for ruining our sleep.
To put this to the test, the researchers studied the Hadza of Tanzania, the San
of Namibia and the Tsimane of Bolivia, fitting their volunteers with
wristwatches that monitor sleep.
"All three groups have pretty much the same sleep duration and pretty much the
same timing of sleep," said Prof Siegel.
"This gives me reasonable confidence that they reflect the common human biology
and they are not a function of their particular situations, which are
different."
As well as discovering that the average sleep duration was six hours and 25
minutes, the researchers also found the participants very rarely took naps.
While some European documents suggested that people used to wake up for a while
during the night, sleeping in two shifts, the researchers found this was not
the case with the hunter gatherers.
Surprisingly, natural light did not have as big an influence as was thought.
Most people fell asleep on average 3.3 hours after sunset.
However, temperature was an important factor.
"What we saw was quite striking - that sleep is occurring during this period of
falling temperature and when the temperature hits bottom, they wake up," said
Prof Siegel.
"This is quite surprising."
And despite the fact that these traditional societies slept less than the
National Sleep Foundation's recommended seven to nine hours a night, the
researchers said they did not grumble about being tired.
Insomnia was also extremely rare - and two of the groups did not even have a
word for it.