Old wisdom said we were either morning larks or night owls. Simple. Binary. The early risers were supposed to be healthier, smarter, more disciplined. The night owls? Messy. Unhealthy. Late to work.
New data tears that up.
It’s not a two-way street. It’s five.
Researchers published this in Nature Communications. They didn’t just look at when you fall asleep. They looked inside the brain. Using machine learning on 27,00 UK Biobank participants, they mapped chronotypes—how we wake and sleep over 24 hours—against brain imaging.
Le Zhou, the lead neuroscientist at McGill University, noticed something striking.
The participants actually have different biological patterns showing in our brain images.
It wasn’t just habits. It was biology.
Three kinds of owls
The breakdown surprises you if you only knew the “night owls are lazy” stereotype. Three subtypes were night owls. Each weirdly specific.
First, the high-performance night owl. Smart. High cognitive performance. But also risky behaviors and trouble regulating emotions. Sharp, but edgy.
Second, the vulnerable night owl. Less activity. More smoking. This group carries the heavy health hit—depression, heart disease, diabetes. They fit the old bad news about late sleepers, but for very specific reasons.
Then there’s the male-biased night owl. Skews male. Higher testosterone. More cigarettes. More alcohol. More cannabis. It explains, biologically, why so many guys claim they can’t sleep before 2 AM. It’s not just stubbornness.
Two kinds of birds
Two subtypes rose early. But even here, the split is real.
The classical early bird. This is the poster child. Efficient brain networks. Stable emotions. Low risk-taking. They drink less. Smoke less. They are, statistically, the healthiest group in the study.
The female-biased early bird? Not quite as smooth. Skews female. Linked to lower testosterone. Menstrual issues. And higher rates of depressive symptoms. Being an early riser doesn’t automatically grant health immunity, especially depending on who you are.
Sonja Schütz at University of Michigan notes these findings matter. Modern life is chaotic. Knowing your specific sleep pattern could help explain why you feel the way you do.
Correlation isn’t causation
But pause.
We don’t know which comes first. The brain shape or the sleep schedule.
Charlene Gamaldo from Johns Hopkins points this out. She wasn’t on the study, but she sees the flaw clearly. The data is self-reported. It shows associations, not cause and effect. Maybe the brain differences cause the sleep pattern. Maybe the lifestyle choices cause both.
“We cannot say from this data alone,” Zhou admits. “Whether the brain differences or health outcomes are the cause or the consequences.”
His team is digging into genetic data next. Trying to untangle the knot of environment, hormones, and genes.
We knew we didn’t all fit the mold. Now we know there are five different molds. None of them are perfect. Which one are you? And more importantly—does knowing the shape of the cage help you escape it? Or does it just tell you how deep the bars go?
