A study of a remote Africa tribe wearing actigraphs suggests for the first time that a 50-year-old theory on animal sleep patterns applies to humans, as Jim Drury reports.
STORY: Tracking members of Tanzania's remote Hadza tribe with fitbit-like devices has uncovered clues about human sleep. Researchers say the Hadza were perfect test subjects. SOUNDBITE (English) DAVID SAMSON, ASSISTANT PROFESSOR OF ANTHROPOLOGY AT UNIVERSITY OF TORONTO MISSISSAUGA (UTM), SAYING: "In the West 99 percent of every individual that lives in a post-industrial context is exposed to light pollution. So the Hadza are exposed to almost no light pollution at all. And finally they are a group that uses foraging to survive, so they're hunter gatherers. They're using the same subsistence strategy that our ancestors used in the same ecology for essentially for 1.8 million years." Thirty three adults from the tribe wore actigraphs on their wrists during the trial. SOUNDBITE (English) DAVID SAMSON, ASSISTANT PROFESSOR OF ANTHROPOLOGY AT UNIVERSITY OF TORONTO MISSISSAUGA (UTM), SAYING: "We found something quite surprising. In fact we found that their sleep was incredibly asynchronous. So by this I mean that it was very very rare that any of the individuals were asleep all at the same time. In fact over 200 hours of our studies so almost 14,000 epochs, that is minutes analysed throughout the nighttime period and only 18 of those epochs where all the adults were asleep." It suggests for the first time that the Sentinel Theory applies to humans - not just animals. The theory postulates that large groups almost always contain members who are awake, to protect others from danger. SOUNDBITE (English) DAVID SAMSON, ASSISTANT PROFESSOR OF ANTHROPOLOGY AT UNIVERSITY OF TORONTO MISSISSAUGA (UTM), SAYING: "When you're in REM, you're about as dead to the world as you'll ever be. So it gives you all these cognitive benefits, emotional regulation and memory consolidation, all these really incredible benefits. But you have to be sleeping securely to be able to go into this stage. So what we think is that having these sentinalised groups was one prerequisite, was one ingredient, that helped humans get better sleep quality throughout evolutionary time." By showing that sleep variation developed evolutionarily, researchers hope to make clinicians pause before diagnosing patients with sleep disorders.