Morning Person or Late Riser?

Research shows that adolescents have a biological need to sleep more.

Till Roenneberg at the University of Munich is especially concerned with the sleep cycle of adolescents. In a landmark study of the sleeping habits of 25,000 people aged between 8 and 90, Roenneberg calculated the "mid-point" of each person's sleep cycle - the time halfway between when they went to bed and when they woke up on days free of work obligations.

He found that children tend to sleep later and later in the morning until they reach about age 20. At that point, there is an abrupt change in sleeping habits, and the mid-point starts getting earlier and earlier again. Roenneberg believes such a sudden shift suggests a biological cause and serves as the first-ever maker for the end of adolescence. The study also reflects the trend for girls to mature faster than boys: the women in the study that slept the latest were 19.5 years of age compared to 20.9 years of age for the men. Roenneberg's research involving teenagers has highlighted the unique sleep needs required by this age group: adolescents sleeping late should no longer be considered lazy, but as exhibiting normal biological traits for their age. Roenneberg's study has also sparked a debate about the early start of the school day, and whether it should be adjusted to account for teenagers' need for more sleep.

The early bird gets the worm?

Benjamin Franklin's well-known proverb "Early to bed and early to rise makes a man healthy, wealthy and wise" (from his Poor Richard's Almanac) not only gives larks a smug sense of superiority, but also reflects the larger trend of society to view sleeping late as a character flaw. Historically, this may have been due to our agrarian ancestors' need to rise with the sun in order to accomplish a full day's work. However, numerous studies have since refuted the claim that there is any health, socioeconomic, or cognitive benefit to following Franklin's advice.

Moreover, new evidence shows that the most important factor in determining a person's morning or night preference is not their willpower but- you guessed it - their DNA. Scientists believe interactions between a dozen or more genes located in the hypothalamus in the brain, and the polymorphisms or differences in those genes, have a strong influence on circadian rhythms. In genetics, variation of traits within a population is often key, and, as Dr. Christopher R. Jones, the medical director of the Sleep-Wake Center at the University of Utah points out, "The whole tribe is better off if someone is up all the night, listening for a lion walking through the grass."