Q: My husband and I have been together for 10 years. Even in the days when we were dating and living separately, we had different sleep schedules, and we still do. He’s an early riser; I’m a night owl through and through. He doesn’t understand how I do it, and frankly, I don’t know how he manages to enjoy his mornings so much. Do personality differences explain why people have different sleeping habits/schedules? 

A: Your sleep schedule is partially biological, meaning that there are specific genes that play a role in deciding whether you’re an early bird or night owl. But our sleep schedule can also be affected by environmental circumstances such as work, family, or our health; these factors may also force us to adjust our sleep schedule

But perhaps more interesting is that research actually does indicate that early birds and night owls have far different personalities, differences that go beyond sleep schedules. In fact, some studies suggest that night owls tend to possess three personality traits known as the “dark triad.” These traits are psychopathy (psychologically manipulative tendencies), Machiavellianism (a willingness to harm others in pursuit of a personal goal), and narcissism (a self-obsessed personality).

Researchers have drawn significant parallels between being a night owl and having a predisposition for committing crime, engaging in risky sex, and making impulsive decisions. This has caused some psychologists to speculate if night owls may have evolved to prefer low light conditions because it makes it harder for others to catch them at whatever they’re doing. It’s also important to keep in mind that being a night owl doesn’t make you a bad person—but you may be more likely to take risks that other people skirt away from.

Early risers, on the other hand, may more often be team players, with more leadership-oriented personality traits. They also show a willingness to sacrifice personal desires for the greater good. But our sleep schedules don’t define us, and there are plenty of early birds with dark traits, and night owls with altruistic tendencies. This means that the time you prefer to sleep doesn’t define your personality: What you do while you’re awake does!