Benjamin Franklin once said, "Early to bed and early to rise makes a man healthy, wealthy, and wise." But in Franklin’s time most people slept in an unconsolidated fashion: They went to "first sleep" shortly after the sun went down, and woke four or five hours later for a few hours of activity before returning to "second sleep." Franklin himself liked to use the time between sleeps one and two to read naked in a chair.
Industrialization and electric lighting put the unconsolidated sleep pattern to rest, so to speak, and today most adults in the U.S. are expected to work from mid-morning to mid-evening — the "nine to five," as Dolly Parton crooned — and, if they’re very lucky, sleep a solid eight hours from night to morning.
Mounting research suggests that differences in lifestyle, personality, brain functioning, and even brain physicality define two distinct chronotypes (a person’s characteristic sleep pattern), which could roughly be defined as "night owls" and "morning larks." Morning larks, those who naturally wake up early and are energized in the pre-lunch hours, are more suited to the typical American work schedule, while the propensities of night owls put them at odds with it, leading them to suffer from chronic social jetlag.
Only an estimated 10 percent of the global population are morning larks, and roughly twenty percent are night owls, with the rest of us falling somewhere in between. Night owls are more prone to depression and are more likely to smoke and drink, and while they’re potentially smarter, their academic abilities fall short of early birds (possibly because they were half-asleep for most of school). It gets worse: A study published in 2013 found that night owls are more likely to have a cluster of personality traits known as the "Dark Triad" — narcissism, Machiavellianism, and psychopathy. Morning larks, conversely, have been found to be more moral, though new research cautions that those findings may be dependent on the time of testing.
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Another study, also published in 2013, found that the quality of the white matter in night owls’ brains was diminished, indicating true structural differences between early and late risers. White matter is brain tissue that facilitates communication among nerve cells, and diminished quality in this tissue has been linked to depression and disruption of cognitive functioning. Lead researcher Jessica Rosenberg speculated that the diminished white matter might be due to that chronic social jetlag effect, but cause and effect has not been definitively established.
One’s circadian rhythm does change over time — babies are often up at dawn, while teenagers are zombie-esque until the afternoon — and there are certain things you can do to adjust your natural rhythms, such as avoiding light in the hours before bed, seeking light upon waking, and regimenting sleep and wake time. But there’s a great deal of evidence that our essential propensity for larkness or owlishness is rooted in genetics. Genetic variation can affect a person’s sleep and wake cycle by up to an hour, and, gruesomely, can help predict what time of a day a person will die.
One thing both groups (and those of us in between) have in common: We probably aren’t getting enough sleep. A December, 2013 Gallup poll found that Americans average less than seven hours of sleep a night — more than an hour less than Americans slept per night in 1942. From 2006 to 2011, the market for over-the-counter sleep aids grew 31 percent.
