It is almost impossible for us to imagine the life of our great-grandparents 100 years ago. Even then, most did not have electricity.
How did they get around at night without street lights or flashlights? What were they doing when it got dark?
We have lost almost all memory.
But an English team of neuroscientists (brain specialists) and anthropologists (human specialists) sought to understand at least how they slept. .
And they found it! They have just published a fascinating study on this subject in the scientific journal Current Biology [1]. [1].
TO THE END OF AMAZONIA
To do so, they set out to study the few tribes that still lack electricity today: the Hadza in Tanzania, the San in Namibia and the Tsimane in the Amazon rainforest.
They don’t go to bed with the sun.
On the contrary, they gather around the fire and in the moonlight (when there is any). They eat, tell stories, sing, dance.
It is only after an average of three and a quarter hours that they finally fall asleep when the night is well advanced.
They do get up at sunrise, on average 7h45 later. But in the meantime, they spend about 1 hour and 20 minutes awake, to accomplish various tasks, such as manning watchtowers, keeping wild beasts away, keeping the fire going.
So in all, they only get 6:25 hours of actual sleep.
They therefore sleep less than the inhabitants of industrialized countries who have, on average, between 7h and 7h30 of sleep.
BODY TEMPERATURE FLUCTUATES WITH THE SUN CYCLE
Another discovery of these researchers during this study is that the natural rhythm of sleep is dictated by the temperature of the body. The men of these tribes fall asleep when their body temperature drops.
This is because the temperature in the center of the human body fluctuates in a 24-hour cycle.
Since we are a diurnal species, that is, a species that naturally lives during the day and sleeps at night, this temperature cycle tends to synchronize with the sun cycle.
This mechanism is biologically useful. It saves us energy.
Since the day is warmer than the night, having our reference temperature higher during the day than at night saves us energy. The regulatory effort is less. Like a house thermostat, turn it down at night to keep the electricity bill from blowing up.
It is true that the price of food calories is so low today that we no longer have to worry about saving money there.
We often have too many. We would like to burn more. It was not like this for millions of years. Without a doubt, it is thanks to these extreme subtleties of our bodies, which we most often ignore, that our ancestors survived, and thanks to which we live today.
WHAT HAVE WE DONE WITH OUR NATURAL SLEEP CYCLE?
On our side, the least that can be said is that the time of sunrise and sunset no longer matters in our lives.
We no longer have the faintest idea of what our “natural” sleep cycle would be.
Granted, most of us still go to bed at night when our watch says 11p.m. or midnight.
But in all likelihood, our grandchildren who will live in 2100 will find it curious, implausible, that humanity has continued to go to bed at night, without any particular motive.
They will certainly be able to decide to create their own sleep-wake rhythm, each in their own way.
Indeed, thanks to e-learning and teleworking, they will probably no longer even have the constraint of office and school hours!
They will live to the rhythm of the stock market and the Internet which, as we know, never stops. Some will do their shopping at 3 in the morning, others will have breakfast at 6 in the evening.
Many residents of New York, Las Vegas or Hong Kong already live like this.
Our way of life will seem outdated, anachronistic to them. They will be amazed by reading history books. Or maybe not even that, because history books will be out of fashion.
But that’s not for certain.
REMEMBER OUR NATURE
« “Hunt the natural, it comes back at a gallop” , says the proverb.
To forget that we are human beings, that our bodies are such an incredibly subtle and complicated ecosystem, is dangerous.
Already today, we suspect a link between depression, mental illness, early Alzheimer’s, and sleep disorders which are all too often fought with sleeping pills.
My conviction is that humans will not be able to keep ignoring the fact that they are a “diurnal animal species”, which imposes certain constraints on them, such as sleeping at night. .
Cheers!
Jean-Marc Dupuis
