Can't get out of bed in the morning? Allow science to tell you why—and whether or not you can change that.

I’m awful in the mornings. Can science fix me?

Maybe not, but it can explain why you’re such a sleepyhead (which may or may not be of interest to your boss). “There are morning people and evening people,” says Sonia Ancoli-Israel, director of education at UC-San Diego’s Sleep Medicine Center. “We call them larks and owls.” Which one you are has to do with your circadian system.

How does my circadian system work?

A region of 20,000 nerve cells in your brain called the suprachiasmatic nucleus keeps your body on schedule throughout the day, regulating everything from hormone levels to when you digest food. And, of course, when you feel sleepy.

How does that explain me?

Larks are “phase advanced,” meaning they feel tired early in the evening. Owls are “phase delayed”—a pattern most common in teens and young adults—and don’t feel tired until late at night.

Should I be concerned?

Larks do have a mental edge. In 2013, a study found that early and late risers have structurally different brains. Larks have more quality white matter, which helps nerve cells communicate.

Can I change that?

A little bit. Your circadian rhythm changes over your lifetime. Babies wake at dawn, while teenagers can’t get out of bed before noon. As adults age, mornings typically get easier. You can also hack your clock by sticking to a regimented sleep schedule and avoiding light before bed. Light receptors in the eye tell your brain when to call it a night.

Can I blame this on genetics?

You bet! In 2012, scientists discovered a single nucleotide near a gene called “Period 1” that determines whether you’re an owl, a lark, or in between.