Animal studies suggest that being a morning person or an evening person may be built into our genes, like having red hair or blue eyes. This may explain why those of us who are early-to-bed, early-to-rise types, or late-to-bed, late-to-rise types, find it so hard to change our behavior.

The Octodon degu, a frisky laboratory rodent whose name comes from its curious back teeth, which resemble the number eight when you look down on them, is helping clarify the role heredity plays in our daily time sense. Degus are rapidly scampering up the research animal popularity chart because they run around, eat, and socialize in the daytime. This fact appeals to scientists who investigate biological clocks, as they typically work the day shift, too.

Degus love their running wheels, and spend hours working out. Some degus run mainly in the morning, others favor the evening, and the rest show no special preference, Susan Labyak of the University of North Carolina and her colleagues found. They were the first to document morning and evening traits in the laboratory in day-active rodents, not specially bred for these characteristics.

Of the forty-nine degus Labyak's group studied, about one in ten was a distinct morning type, its activity peaking around 7 A.M. About two in ten were distinct evening types, most active around 9 P.M. The rest fell somewhere in between. Just like us.

If you like to linger over your coffee to read the morning paper, you're probably more of a lark. Owls often skip breakfast, and they're always rushing to get to work in the morning. Think of Dagwood Bumstead perennially colliding with the hapless mailman as he races out the door, an act so etched in the public consciousness that it is featured on a U.S. postage stamp. If you do laundry or surf the Internet at midnight, you're probably an owl. If you occasionally get up at dawn to go fishing, and sometimes stay up long past your usual bedtime at parties, you're a happy hummingbird.

Some of us think of ourselves as night people, but humans can't truly claim the night as home territory. We are programmed to function best in the daytime. We can't see in the dark. Even if we insist on flip-flopping our schedules to work at night, Mother Nature isn't fooled. Night is still the down time on the body clock. Morningness and eveningness are as far apart as humans get.

Artist Edward Hopper often portrayed these extremes. In Cape Cod Morning, a woman already dressed for the day gazes out her living room window at trees bathed in dawn light. In Nighthawks, a man and woman in evening clothes sip coffee in an all-night diner.

Lark and owl traits influence many aspects of daily life, including when we feel most alert and when we sleep best. These traits determine when we most enjoy meals, exercise, sex, and other activities. They also affect when we choose to work, or would, if we could.

If you're a lark, you probably wouldn't enjoy a job as a nighttime bartender. If you're an owl, you'd have to struggle to report the morning news. Lark/owl traits may play a bigger role in job choice than most of us suspect. Emergency room physicians, for example, spend more time working at night throughout their lives than physicians in other specialties. It's no mere coincidence that ER doctors prove to be owls more often than larks. Researchers asked every emergency medicine resident in the U.S. taking an annual exam in 1995 to answer a morningness/eveningness survey. Mark Steele and his colleagues at the University of Missouri-Kansas City School of Medicine handed out 2,600 surveys, and got close to 2,000 back. More of the residents tended toward eveningness than is true for the general population.

Most of us adapt pretty well to life's demands. Cartoonist Scott Adams started Dilbert while holding a full-time job, penning it between 5 A.M. and 7 A.M. before going to work. Since he made it easy for readers to contact him, putting his e-mail address right on the strip, we wrote him in 1995, shortly after he left Pacific Bell to work on Dilbert full-time.

"I'm quite tuned into my rhythms," Adams replied. "I never try to do any creating past noon. And I only exercise in late afternoon. I do the strip from 6 A.M. to 7 A.M. Then I write for a few hours. I only ink the strip afternoons or evenings when my hand is steady. I can't ink in the morning.

"I created my second career," he claimed, "by 'discovering' the morning."

In 1999, Dilbert made its television debut. We wrote Adams again to see whether his life had changed. "My schedule is completely reversed now, because of working with Hollywood," he reported. "They're night owls. So I sleep until 7 A.M. and work off and on until midnight most nights. But I still don't do creative work in midafternoon. I do my mindless stuff, like inking or scanning then."

Like Adams, most of us view our schedules as a compromise between what we have to do, and what we would like to do. Most people say they would like to sleep later, for example. College students who seldom go to bed before 2 A.M. almost certainly will turn off the lights earlier after they graduate and enter the daytime workforce, and they will become even more larkish after they become parents. They might complain, but most will manage. By the time they are in their sixties and over, most will be comfortable going to sleep and getting up earlier than they did when younger. All of us might feel and function better, though, if we could synchronize more of our required activities with our natural rhythms throughout our lives.

Indeed, the recent rise of flextime schedules in the workplace, allowing workers to start and stop as much as two or three hours earlier or later, as they wish, is a positive step in this direction. One in five full-time American workers now has flexible hours.

A gene may govern owlish behavior in humans. Daniel Katzenberg of Stanford University and his colleagues assessed morningness/ eveningness traits in 410 randomly sampled adults with a questionnaire. They also drew blood samples from the respondents, and examined the makeup of a gene called Clock known to exert influence over biological rhythms. Comparing results from the two tests, they estimated that the owls lagged ten to forty-four minutes behind larks in their preferred times for various activities and for sleep, a significant difference. Moreover, a particular pattern consistently appeared in part of the Clock gene in owls, but not in larks. Genetic studies such as this may prove a two-edged sword. They potentially could help workers decide which jobs suit them best. But they also could be used to discriminate against workers whose genetic traits do not correspond to an employer's criteria. That would be unfortunate, because lark/owl tendencies do not rule most people's lives. High motivation for all but extreme larks and owls probably has a much bigger impact on job success.

Timewise Tips

If you are a lark:
Spend time outside in the afternoon or early evening. This tactic should help you stay up later, and may help you sleep later in the morning, too. It's especially helpful to older persons, who often go to bed as early as 8 P.M. and find themselves awake, with nothing to do, at 3 A.M.

If you are an owl:
Sleep with blinds or curtains open, and let daylight awaken you naturally. It's a gentle process and much easier to take than the annoying bleat of an alarm clock. Set the alarm anyway. Hey, set two alarms, for safety's sake.

Tips for Couples and Families:
Civility is the key to getting along despite individual differences, according to Judith Martin, who writes the popular syndicated Miss Manners column. "Miss Manners never excuses rudeness at any hour or under any circumstances," she says. But she excuses evening people from sociability until they have had their coffee. "Everybody who is ambulatory," she maintains, "is required to say, 'Good morning,' and to pass the sugar when asked and to reply to comments and questions addressed to them.... Being excused from sociability means that they may reply only by making 'Umm' and 'Uh' noises with the mouth closed, and need not offer conversational encouragement."

Summing Up
If you are right-handed, you may be able to learn to use your left hand. A Type A personality may learn to relax. An overweight person can slim down. In the same way, most larks and owls can manage most schedules as their jobs, families, or social lives demand. Some will feel more dissonance than others when they try to follow clocks at variance with their natural proclivities. Extreme larks and owls report the most problems. They may find it difficult, if not impossible, to function in some situations. They are not sick. They are not lazy. They are not lacking in motivation. Happily, in our increasingly twenty-four-hour world, there are plenty of spots where most larks, owls, and hummingbirds can find a secure perch.