On Monday, a trio of American scientists won the Nobel Prize in Medicine or Physiology for their research on circadian clocks, the inner biological timepieces that tell organisms when to wake up, when to be active, and, most crucially, when to go to sleep. Their work on the underlying genetics of fruit fly sleeping patterns has shed light on a fundamental human experience: the undeniable urge to take a midday nap.

The prize-winning work that Brandeis University geneticists Jeffrey Hall, Ph.D. and Michael Rosbash, Ph.D., together with Rockefeller University’s Michael Young, Ph.D. started on in the 1980s revealed a genetic mechanism that causes fruit flies to get sleepy at specific times of the day and hinted that other animals — like humans — succumb to the same innate forces when the environment is right.

“If challenged with conditions that have long, warm days, then fruit flies tend to have a siesta,” University of Southampton geneticist Herman Wijnen, Ph.D., who was a postdoc in Young’s lab and now also studies circadian rhythms in fruit flies, tells Inverse.

“This is also what we see in people that live in the tropics, to some extent — the tendency to stay indoors, maybe have a nap or lie down when it’s really warm outside. That’s quite natural.”

This fruit fly is used by researchers at Oregon State University for studies of the genes that control the biological clock in many animals, including humans. (Photo courtesy of Oregon State University)
Research on the biological clock in fruit flies has led to a greater understanding of the urge to nap in humans.

The research of the Nobel Prize-winning scientists revealed a particular fruit fly gene, named “period,” that carries the instructions for producing a sleep-related protein and seems to function on a 24-hour clock. This gene, they found, becomes most active at night, causing a buildup of the related protein. Once enough of these proteins are stacked up — largely a function of how many hours have passed — the gene stops pumping out those proteins, and they start breaking down during the fly’s waking hours.

During warm days, the processing of this gene becomes inefficient and the accumulation of its product is delayed, as shown in subsequent research by Isaac Edery from Rutgers University and Paul Hardin from Texas A&M. This is associated with the siesta behavior of flies observed under those circumstances.

For a fruit fly, napping during long, warm days could spell the difference between life and death. At temperatures above 30 degrees, Wijnen explains, fruit flies are at risk of going sterile and drying out, which is likely why they seek shade and enter a period of low activity when the sun is hottest. This sort of “siesta-like behavior” has also been observed in mice and other animals, and while there hasn’t been any published research yet showing that humans nap for the same genetic and environmental reasons, it seems likely that there is some overlap between us and our napping animal relatives. Afternoon siestas, after all, are most popular in the Mediterranean and southern Europe, where the middle of the day is bright and hot.

Buster's concerns are not unfounded.

Building on the work on Hall, Rosbash, and Young, many circadian rhythm scientists, notably Joseph Takahashi of the University of Texas Southwestern Medical Center in Dallas, have shown that the body clock mechanisms centered around the period gene seem to be conserved across most species, including humans.

If future research confirms that is indeed the case, then we might want to do a better job of working with what our genes dictate. “It could be we’re actually tricking ourselves into a summery paradigm more so than would be natural,” speculates Wijnen, pointing out that we use artificial light to extend our days and artificial heat to stay warm in ways that aren’t consistent with what humans evolved to deal with. It doesn’t help that our indoor lights are much weaker than daylight, he points out, which can be interpreted as more of a wintery signal and can lead to inadequate synchronization of our clock.

“The net effect may, therefore, be disruptive to our internal timekeeping, which comes with adverse health effects.”

Most humans wouldn’t argue that we wouldn’t be better off with a couple more hours of sleep, and as research building on the Nobel Prize-winning work continues we might someday gather the evidence we need to trigger a cultural shift in the way we allot time for sleep. In the meantime, Wijnen says, we should probably just sleep when we feel like it.

“There are studies that show there are real benefits to taking a nap, and part of it may be due to the fact that we’re having relatively shorter nights than if we would just be exposed to natural light conditions,” he says. “We may be more prone to needing those naps.”

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