What makes somebody a morning person or a night owl?
The vast majority of people are neither strong morning nor strong evening types — just day types. “Even though somebody will swear he’s a morning person or a night owl, that’s often a false perception,” Brown said. However, 15 to 30 percent of people clearly do not follow the normal 24.1-hour cycle. “Their natural period runs shorter or longer than that, a difference that can change the time they normally fall asleep — and, later, spontaneously awaken — by a couple of hours.”
“For people who are extreme evening types, 1 o’clock in the morning is still an active time. Those individuals also naturally awaken much later in the morning. The great majority of younger college students fall into this category.
“There is a strong genetic component determining whether a person is an evening or a morning type in their activity times,” said Penn State psychology professor Frederick Brown.