All animals sleep, from the lowest invertebrate worm to the highest mammal, cats. Why we all sleep has been elucidated by a groundbreaking study done in Israel, showing that sleep is when our neuronal DNA is most efficiently repaired. When we sleep is another question entirely. Now, a groundbreaking study at Rutgers University has discovered that on hot days, the peoples of the Mediterranean and their fruit flies all take naps — and discovered genetic regulation of siesta in the insect.
It makes sense to sleep at night because we can’t see what we’re doing and cannot hunt, gather or work efficiently. In parallel, nocturnal species found an evolutionary advantage in foraging or hunting, etc., when their rivals are senseless.
As for the afternoon nap, certain peoples in cold climes have been known to charge their Mediterranean counterparts of laziness. But first of all, some research has correlated between failure to take that schlafstunde and road accidents. Second, Rutgers now reports on a gene in fruit flies that suppresses the siesta when the temperature turns cold. Suitably enough, they named the gene daywake.
The very evolution of a genetic mechanism to regulate siesta in the heat of the day suggests that the nap has biological significance, the researchers explain in Current Biology.
Sleep and the fruit fly
A recent study suggesting that, out of all creatures, one lone being — the male fruit fly — can survive without sleep has been roundly savaged. If it's true he's the sole exception, though critics have argued out that fruit-fly life span is so short that if the male fails to slumber, even throughout his life, it hardly matters.
So let's leave male Drosophila out of it and assume that sleep we must. But what could the evolutionary importance of the siesta be?
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It isn’t that fruit flies get into more traffic accidents if denied a nap. It’s that if they don’t need one because the heat is not enervating them, they can stay awake and do things, and be more efficient.
“This gene contributes to behavioral flexibility, or the ability to hide from the noontime sun when weather is hot but engage in activities good for survival when the weather is cool. That probably helped these flies expand beyond their ancestral home in equatorial Africa to successfully colonize temperate zones around the world,” postulates co-author Isaac Edery, a professor at the Rutgers center.
Don’t confuse a siesta with æstivation, the summer equivalent of hibernation, in which certain animal species from snails to crabs to African lungfish go into a low-metabolic stupor in summer, and “come back to life” when the weather cools and/or it rains.
Interestingly, the daywake gene in the fruit fly is located next to — and slightly overlapping — a gene named “period,” which regulates the flies’ sleep at night (their circadian clock). The two genes interact. In fact, there is a new theory that all genes interact with all genes. But meanwhile, they discovered that daywake is triggered when the flies are exposed to cold temperatures — and whether or not daywake is activated, or whether or not the fly slumbers at midday, it doesn’t affect its sleep at night.
We humans don’t have a daywake gene, but it is entirely feasible that our siesta is regulated by genetic mechanisms we have not yet identified. Do not confuse “genomic sequencing” with having any idea what most of our DNA does. We do not know.