Zacks say their work “suggests that students designing their class schedules might perform best in classes such as art and creative writing during their non-optimal compared to optimal time of day.”24
In short, our moods and performance oscillate during the day. For most of us, mood follows a common pattern: a peak, a trough, and a rebound. And that helps shape a dual pattern of performance. In the mornings, during the peak, most of us excel at Linda problems— analytic work that requires sharpness, vigilance, and focus. Later in the day, during the recovery, most of us do better on coin problems—insight work that requires less inhibition and resolve. (Midday troughs are good for very little, as I’ll explain in the next chapter.) We are like mobile versions of de Mairan’s plant. Our capacities open and close according to a clock we don’t control.
But you might have detected a slight hedge in my conclusion. Notice I said “most of us.” There is an exception to the broad pattern, especially in performance, and it’s an important one.
Imagine yourself standing alongside three people you know. One of you four is probably a different kind of organism with a different kind of clock.
LARKS, OWLS, AND THIRD BIRDS
In the hours before dawn one day in 1879, Thomas Alva Edison sat in his laboratory in Menlo Park, New Jersey, pondering a problem. He had figured out the basic principles of an electric lightbulb, but he still hadn’t found a substance that worked as a low-cost, long-lasting filament. Alone in the lab (his more sensible colleagues were home asleep), he absentmindedly picked up a pinch of a sooty, carbon-based substance known as lampblack that had been left out for another experiment, and he began rolling it between his thumb and forefinger—the nineteenth-century equivalent of squeezing a stress ball or trying to one-hop paper clips into a bowl.
Then Edison had—sorry to do this, folks—a lightbulb moment.
The thin thread of carbon that was emerging from his mindless finger rolling might work as a filament. He tested it. It burned bright and long, solving the problem. And now I’m writing this sentence, and perhaps you’re reading it, in a room that might be dark but for the illumination of Edison’s invention.
Thomas Edison was a night owl who enabled other night owls. “He was more likely to be found hard at it in his laboratory at midnight than at midday,” one early biographer wrote.25
Human beings don’t all experience a day in precisely the same way. Each of us has a “chronotype”—a personal pattern of circadian rhythms that influences our physiology and psychology. The Edisons among us are late chronotypes. They wake long after sunrise, detest mornings, and don’t begin peaking until late afternoon or early evening. Others of us are early chronotypes. They rise easily and feel energized during the day but wear out by evening. Some of us are owls; others of us are larks.
You might have heard the larks and owls terminology before. It offers a convenient shorthand for describing chronotypes, two simple avian categories into which we can group the personalities and proclivities of our featherless species. But the reality of chronotypes, as is often the case with reality, is more nuanced.
The first systematic effort to measure differences in humans’ internal clocks came in 1976 when two scientists, one Swedish, the other British, published a nineteen-question chronotype assessment. Several years later, two chronobiologists, American Martha Merrow and German Till Roenneberg, developed what became an even more widely used assessment, the Munich Chronotype Questionnaire (MCTQ), which distinguishes between people’s sleep patterns on “work days” (when we usually must be awake by a certain hour) and “free days” (when we can awaken when we choose). People respond to questions and then receive a numerical score. For example, when I took the MCTQ, I landed in the most common category—a “slightly early type.”
However, Roenneberg, the world’s best-known chronobiologist, has offered an even easier way to determine one’s chronotype. In fact, you can do it right now.
Please think about your behavior during “free days”—days when you’re not required to awaken at a specific time. Now answer these three questions:
1. What time do you usually go to sleep?
2. What time do you usually wake up?
3. What is the middle of those two times—that is, what is your midpoint of sleep? (For instance, if you typically fall asleep around 11:30 p.m. and wake up at 7:30 a.m., your midpoint is 3:30 a.m.)
Now find your position on the following chart, which I’ve repurposed from Roenneberg’s research.
Chances are, you were neither a complete lark nor an utter owl, but somewhere in the middle—what I call a “third bird.”* Roenneberg and others have found that “[s]leep and wake times show a near-Gaussian (normal) distribution in a given population.”26 That is, if you plot people’s chronotypes on a graph, the result looks like a bell curve. The one difference, as you can see from the chart, is that extreme owls outnumber extreme larks; owls have, statistically if not physiologically, a longer tail. But most people are neither larks nor owls. According to research over several decades and across different continents, between about 60 percent and 80 percent of us are third birds.27 “It’s like feet,” Roenneberg says. “Some people are born with big feet and some with small feet, but most people are somewhere in the middle.”28
Chronotypes are like feet in another way, too. There’s not much we can do about their size or shape. Genetics explains at least half the variability in chronotype, suggesting that larks and owls are born, not made.29 In fact, the when of one’s birth plays a surprisingly powerful role. People born in the fall and winter are more likely to be larks; people born in the spring and summer are more likely to be owls.30
After genetics, the most important factor in one’s chronotype is age. As parents know and lament, young children are generally larks. They wake up early, buzz around throughout the day, but don’t last very long beyond the early evening. Around puberty, those larks begin morphing into owls. They wake up later—at least on free days—gain energy during the late afternoon and evening, and fall asleep well after their parents. By some estimates, teenagers’ midpoint of sleep is 6 a.m. or even 7 a.m., not exactly in synch with most high school start times. They reach their peak owliness around age twenty, then slowly return to larkiness over the rest of their lives.31 The chronotypes of men and women also differ, especially in the first halves of their lives. Men tend toward eveningness, women toward morningness. However, those sex differences begin to disappear around the age of fifty. And as Roenneberg notes, “People over 60 years of age, on average, become even earlier chronotypes than they were as children.”32
In brief, high school– and college-aged people are disproportionately owls, just as people over sixty and under twelve are disproportionately larks. Men are generally owlier than women. Yet, regardless of age or gender, most people are neither strong larks nor strong owls but are middle-of-the-nest third birds. Still, around 20 to 25 percent of the population are solid evening types—and they display both a personality and a set of behaviors that we must reckon with to understand the hidden pattern of a day.
Let’s begin with personality, including what social scientists call the “Big Five” traits—openness, conscientiousness, extraversion, agreeableness, and neuroticism. Much of the research shows morning people to be pleasant, productive folks—“introverted, conscientious, agreeable, persistent, and emotionally stable” women and men who take initiative, suppress ugly impulses, and plan for the future.33 Morning types also tend to be high in positive affect—that is, many are as happy as larks.34
Owls, meanwhile, display some darker tendencies. They’re more open and extroverted than larks. But they’re also more neurotic— and are often impulsive, sensation-seeking, live-for-the-moment hedonists.35 They’re more likely than larks to use nicotine, alcohol, and caffeine—not to mention marijuana, ecstasy, and cocaine.36 They’re also more prone to addiction, eating disorders, diabetes,