The idea of the virtuous early bird goes back at least to Aristotle, who wrote, in his Economics, that “Rising before daylight is … to be commended; it is a healthy habit.” Benjamin Franklin, of course, framed the same sentiment in catchier terms: “Early to Bed, and early to rise, makes a Man healthy, wealthy and wise.” More recently, there has been a push for ever earlier work starts, conference calls, and breakfast meetings, and a steady stream of advice to leave Twitter and Facebook to the afternoon and spend the morning getting real things done. And there may be some truth to the idea: a 1998 study in the Journal of Personality and Social Psychology suggests that we become more passive as the day wears on. You should do the most important thing first, the theory goes, because, well, you won’t be able to do it quite as well later on.

In last January’s issue of Psychological Science, Maryam Kouchaki and Isaac Smith took that theory even further, proposing what they called the morning morality effect, which posits that people behave better earlier in the day. Their research caught the attention of Sunita Sah, a behavioral scientist at Georgetown University and a professed night owl. For the previous five years, Sah had been studying how different situations influence ethical behavior. “You always hear these sweeping statements: morning is saintly, evening is bad; early to bed, early to rise,” she told me recently. A former physician, she found it plausible that something with such profound health consequences as time of day might also have a moral dimension. But she wondered how strong the effect really was. Were people like her—principled late risers—the exception to the rule? To test the limits of Kouchaki and Smith’s findings, Sah and her colleagues began by looking at the underlying biology.

Our sleep patterns are governed by circadian rhythms, our bodies’ response to changes in light and dark in a typical day. The rhythms are slightly different for every person, which is why our energy levels ebb and flow in ways that are unique to us. This internal clock determines what is called our chronotype—whether we are morning people, night people, or somewhere in between. Chronotypes are relatively stable, though they have been known to shift with age. Children and older adults generally prefer mornings; adolescents and young adults prefer evenings. Figuring out where you fall is simple: spend a few weeks going to bed when you feel tired and waking up without an alarm clock. A quicker alternative is the Horne-Ostberg questionnaire, which presents various scenarios—a difficult exam, twice-weekly exercise with a friend—and determines your chronotype on the basis of what time of day you’d feel most up to confronting them.

Chronotype, of course, doesn’t control wakefulness all on its own. There is also what is known as homeostatic sleep drive. The longer we are awake, irrespective of where we are in our established circadian rhythms, the more fatigue exerts its pressure on us. In morning people, sleep drive and chronotype tend to be aligned. Their internal clocks are pretty well synchronized with their over-all energy levels. For night owls, however, things get complicated. When the sun comes up, the light resets their circadian clocks, telling them to wake up. But, because of their chronotypes, they don’t have much energy and they want to go back to sleep. At night, the reverse happens: one system is telling them to sleep and another is telling them to remain awake. About forty per cent of people fall into this latter category.

Sah began her research by assuming that we are different people at different hours. In a series of studies, she and her colleagues Brian Gunia and Christopher Barnes examined whether time of day affected the likelihood that a person would cheat at a game. They selected their participants by chronotype, focussing on those who fell on either side of the Horne-Ostberg scale—those who preferred morning and those who preferred night. In one study, participants recorded how many number matrices they had solved correctly. In another, they noted how they had performed in a die-rolling task. In both cases, they had the opportunity to cheat—they were allowed to score themselves—and a monetary incentive to do so.

Some people did cheat less in the morning, Sah found, but only if they were early birds to begin with. The opposite was also true: night owls cheated less in the evening. Time of day had less effect on honesty, the group concluded, than did the synchronicity between person and environment. “Our results should really dissipate those stereotypes of morning people being more saintly,” Sah says. “The important thing is the match.” Early birds aren’t ethically superior. And, to the extent that other research suggests that they are, it may just be that they are luckier: modern society, for the most part, is built around their preferences. We are expected to function well early in the morning. We can’t just wake up when our bodies tell us to and work when we feel at our peak.

For Sah, this research is the first part of a broader examination. She is currently studying whether people who have clear ethical responsibilities in their careers—financial advisers, for instance, or doctors—make decisions with greater clarity when their work schedules and chronotypes align. “We need to think not just about ethical decision-making but the quality of the work and the cognitive processes,” she told me. “It’s much better to match people to schedules and structures based on their chronotype than to just force them into a schedule, knowing nothing.” She added, “I probably don’t want to set exams at 8 A.M. if I don’t want my students to cheat.”

Ultimately, the best policy may be to understand and embrace your chronotype. Sah says that it’s incredibly difficult, if not impossible, to overcome your predisposition and train yourself to function better at times that don’t match up with your inner clock. “There’s very little evidence that anything really works,” she says. So, late risers can take heart: they are neither immoral nor slothful. But, as long as the world isn’t operating on their terms, and unless they’re lucky enough to work in a place that endorses flexible scheduling, the early birds may still get the worms.