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If you know someone who can’t start their morning without 3 cups of coffee, don’t assume they frequently stay out late partying—it’s probably genetics.

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It seems like there are two types of people in the world.

Some people are fresh as a daisy first thing in the morning and ready to get a jump on the day. Others are sluggish and bleary-eyed before 10 AM, gripping their coffee like their life depends upon it. Basically, you’ve got your morning larks and your night owls —I’m a night owl— and scientifically, those are real terms.

They refer to a person’s chronotype: the particular calibration of their internal clock that leads them to naturally sleep and wake at a certain time. If your chronotype doesn’t line up with the people around you —like, for example, your two-year-old— you might understandably want to change it. But it’s not clear whether that’s actually possible — and even if you could, you probably wouldn’t like it.

Like most human traits, chronotypes fall on a bell curve. Though the numbers vary between studies, roughly 10 to 20 percent of people are night owls or morning larks, and the majority of people fall somewhere in the middle. And it’s not just a matter of habit or preference: there’s evidence that your chronotype is written in your genes.

A 2016 study found 15 gene variants associated with a morning chronotype, for example. Most of them appeared to play roles in the body’s response to light and in regulating circadian rhythms, or the daily cycles that govern most of the body’s processes. Your chronotype also seems to be heritable.

You’ve got a better chance of being a night owl if one of your parents is, too. Scientists can even detect chronotypes in human cells when they’re grown in culture. In fact, researchers are working on a way to test a person’s chronotype using their blood, so they can time medical treatments to match the natural rhythms of a patient’s body.

And that’s because your internal clock is super important. Nearly half of the genes in your genome follow a circadian rhythm of expression at least somewhere in your body. That rhythm governs not only when you sleep or wake, but your body temperature, eating habits, and hormone activity.

This internal clock is set by a tiny region in the brain’s hypothalamus called the suprachiasmatic nucleus. Like, it decides when to dose you with melatonin to make you sleepy. If you’re the type of person who doesn’t get tired until 2 a.m., that might just be because your body doesn’t start pumping out melatonin earlier.

But your chronotype isn’t just how sleepy you are for an 8 o’clock class. It also seems to correlate with personality. People high in agreeableness and conscientiousness seem to be morning people, for example.

Studies also find that women are a little more likely to be morning people than men. But the strongest factor linked to your chronotype is age. Children generally start out with a lark-ier chronotype, then shift somewhat towards being a night owl in adolescence, and then, after that, most people become more morning-oriented the older they get.

Whatever your age, though, if your chronotype conflicts with your day-to-day obligations, it can cause problems. And let’s be honest, those problems overwhelmingly affect night owls. School and work tend to start early in the morning, and if your body clock doesn’t want you awake until 10, you’re gonna have a bad time.

This is what’s known as social jet lag. It’s a misalignment between biological timing and society’s timing that leaves a person sleep deprived. Social jet lag isn’t just unpleasant — it’s unhealthy.

It’s associated with a higher risk of obesity, insulin resistance, and depression, for starters. And that might be why other studies find that night owls are less happy than morning larks overall. They also suffer from more depressive symptoms, they drink and smoke more, and they report more binge eating behaviors than their early-to-rise counterparts.

So can you change your chronotype? Yes and no. For people with severe circadian rhythm disorders, whose internal clocks are offset dramatically from what’s considered normal, there are a few standard treatments professionals turn to.

They usually involve some combination of light therapy, melatonin supplementation, and chronotherapy, where you go to bed a few hours later every night to reset your internal clock. But it’s really hard to reset your clock and keep it that way. For it to work, you have to get up and go to sleep at the same time every day, even on weekends.

One late night has the potential to reverse everything. Because, ultimately, you’re fighting your DNA. This is why it’s helpful to have a person in your home who starts screaming every morning at 6:30, no matter what. You’re gonna wake up.

The healthiest thing anyone can do, regardless of chronotype, is get enough sleep. So if social jet lag makes people sleep deprived, and changing chronotypes is next to impossible, there’s only one real option.

Society has to change. Schools and workplaces have to accept the fact that different people have different internal clocks, and what’s a perfect hour for one person could spell disaster for someone else. And the good news is that things are changing—slowly.

In 2014, the American Academy of Pediatrics officially recommended that schools start no earlier than 8:30, for example. And the number of workplaces that offer flexible schedules and remote work is steadily increasing. But until there’s more public understanding and accommodation for individual chronotypes, there’s going to be a sizeable portion of the population that just really needs their coffee.

We’ve got an exciting announcement! We just launched Universe Unboxed — science experiment kits from all of us here at SciShow! Universe Unboxed kits are packed with experiments designed for kids elementary school-aged or older.

Like, you know, in their late 30s. Each kit teaches specific science concepts, but we didn’t stop there! In each, we also explain how scientists use those concepts and how they matter in the real world.

Like, in the Brain Teaser kit, you can learn about how gravity works— and how you can use it to make a seemingly impossible stack of nails. And while that might seem like a silly game, it’s the kind of thinking engineers have to do when they design structures to be topple-resistant. I’ve done all the experiments myself and made video demonstrations, so you can see how they’re done.

And they were really fun and weird and surprising! If you want to try them out too, you can find Universe Unboxed kits at a store near you, or at [OUTRO ♪].