The First ‘Morning People’ To Ever Exist

So, why does chronotype variation exist at all? Evolution doesn’t typically preserve traits that don’t serve a purpose. The answer may be one of the more elegant discoveries in the field of sleep science.

In a 2017 study published in the Proceedings of the Royal Society B, a team of researchers studied the Hadza: a hunter-gatherer population in Tanzania, and one of humanity’s closest windows into ancestral living.

Using wrist-worn actigraphy devices, they monitored sleep-wake patterns across the group. They were surprised to find that, over 20 days of observation, all participants were simultaneously asleep for a total of just 18 minutes. One or more individuals were awake, or in a light and easily roused state, during 99.8% of nighttime epochs. The group, in effect, was never fully unconscious at the same time.

Notably, this wasn’t the result of insomnia — or any sleep disorder for that matter. It was chronotype diversity doing exactly what natural selection may have shaped it to do. The authors framed this through the sentinel hypothesis, which holds that group-living animals reduce the vulnerability of sleep by having members awake on a staggered schedule.

In the ancestral environment, where predators were real and hostile neighbors were common, a group that was never entirely asleep was a group far more likely to survive. Morning people weren’t just early risers. They were, in a meaningful sense, on watch. This evolutionary pressure helps explain why chronotype variation has persisted across human populations for so long. It may even predate Homo sapiens itself.

In a 2025 study published in npj Biological Timing and Sleep, researchers found genomic evidence of adaptive introgression. This means, in simple terms, that our chronotype-related variants were inherited from archaic humans, including Neanderthals and Denisovans. Both morning and evening preference alleles appear to trace partly to these ancient populations. The diversity we carry today reflects a very old inheritance.

Over time, these survival-relevant behavioral differences became embedded in the genome. In a 2019 genome-wide association study published in Nature Communications, researchers identified 351 genetic loci associated with morning chronotype (up from just 24 a decade ago) in a meta-analysis of nearly 700,000 individuals. The loci cluster around genes involved in circadian regulation, retinal photoreception and signaling pathways in the hypothalamus and hindbrain.

Your chronotype, according to these findings, is a complex polygenic trait with a heritability estimated at around 50%, shaped by hundreds of small genetic effects acting in concert. Individuals carrying the greatest proportion of morningness alleles wake, on average, 25 minutes earlier than those with the fewest — a modest but measurable biological signature, written into the genome.

Why Even Morning People Can Change Completely

What few people know is that chronotype isn’t a fixed part of our biology. It migrates predictably across the lifespan, and not always in ways that match our social expectations.

Newborns and young children are, almost universally, morning types. In a large 2017 study published in Scientific Reports, spanning over 26,000 individuals from birth to early adulthood, roughly 70% of 0–1 year olds were identified as morning types, with barely 1% showing an evening preference.

But then puberty arrived. The turn toward eveningness begins around age 10, peaks in the late teenage years (around 19 to 21-years old), and then gradually reverses. The breaking point back toward morningness occurs at approximately 15.7 years in girls and 17.2 years in boys, tracking closely with the earlier onset of puberty in females.

By middle age, most of us are waking earlier than we did at 20. By older age, we may be up before dawn without even wanting to be.

This adolescent shift toward eveningness is not a social construct, nor is it a matter of teenagers wanting to stay up watching screens. It’s a biological phenomenon that’s been documented across more than 20 countries on six continents, observed even under controlled laboratory conditions with limited social influence. It correlates with hormonal changes of puberty, not with peer behavior. Telling a 16-year-old to simply go to bed earlier is about as useful as telling someone to change their height.

Notably, Mendelian randomization studies — a method that uses genetic variants to establish causation rather than mere correlation — have found that morning chronotype is causally associated with better mental health outcomes.

More specifically, evening types face a chronic mismatch between their internal clocks and the external demands of early-starting schools and workplaces, a phenomenon researchers call “social jet lag.” This misalignment, sustained over years, is associated with elevated risk for depression, metabolic disturbance and impaired cognition.

To be a night owl in a morning-oriented world is, for many, a low-grade, invisible health burden. It bears noting that the problem here is not the chronotype itself, but the mismatch: night owls who can align their schedules with their biology show markedly fewer of these health disparities.

Morning People Don’t Have To Rely On Willpower

There is a persistent cultural mythology that morning people are simply more disciplined, more virtuous or more likely to succeed. Motivational literature is full of them: the 5 a.m. routines, the cold showers, the quiet triumphs before the rest of the world wakes. And while habits and light exposure do modestly influence sleep timing, the truth is that, for most of us, what time we wake is not meaningfully a matter of choice.

Your circadian clock was set, in part, before you were born, by the accumulated weight of hundreds of genetic variants, some inherited from modern humans, some from archaic ones who walked the earth tens of thousands of years ago. It shifts with your hormones, your age and your environment, but its fundamental phase is largely beyond willpower’s reach.

The morning person who bounds out of bed at 6 a.m. refreshed and ready is not morally superior to the night owl who does their best thinking at midnight. They are simply carrying a different, and equally ancient, piece of our shared evolutionary inheritance.

Curious to know your chronotype? Take the science-inspired Internal Clock Personality Test, and find out whether you’re on team morning people or team evening people.