A friend died recently. She was ninety-eight years old. I was never to try to call her before noon.
She explained that she only could sleep in the morning, that she was awake through the night – while I was sleeping. This happens with older people. We tend to go to bed and rise earlier than the rest of you. For many of us the night brings only fitful sleep, a period of wakefulness. We replenish what remain of our brain cells, or whatever it is sleep does for us, by napping during the day.
Why is it this way? It just might be evolution, something written in our genes to promote survival of our – village.
Scientists recently reported (Proceedings of the Royal Society B and reported in the New York Times) results of a study of sleep patterns of an east African hunter-gatherer people, the Hadza. The Hadza sleeping environment may have similarities to that of earlier humans, researchers said. They sleep outdoors or in grass huts in groups of 20 to 30 people without artificially regulating temperature or light. These conditions provide a suitable window to study the evolutionary aspects of sleep. In their study they found that somebody was always awake. During the period of the study everybody was sleeping for only an average of 18 minutes in a twenty-four hour day. During the night and in the wee hours of the morning it was the grandparents who tended to be awake. And watchful.
The scientists hypothesized that the young folks needed their sleep more than the grandparents. This is because the young folks were the ones who needed light for their work, whether it was gardening, hunting, or caring for the family and protecting against predators and other intruders. The grandparents were tasked with the job of watching through the night. Keeping an eye out for encroaching threats to the village.
So, I thank my friend for her sleeplessness. I am quite sure that her inability to sleep during many nights over many years provided our small village an important degree of safety.
Is it my turn?