Chronotypes, representing genetic predispositions to being morning or evening people, are roughly equally distributed among the population.

“we know that it is under strong genetic control for two reasons first there is a significant degree of heritability so if you are a morning type it's more than likely that one or both of your parents were morning types secondly we now know that there are a collection of genes that will determine to a degree your chronotype and this is why companies like 23 and me will tell you what type you are or they will give you a probabilistic estimation of what type you are last count i think from data from 23andme and there's data from the uk biobank there's about nine different genes that we know of right now that will contribute to your chronotype”

“we know that there is a complement of genes that you are given at birth that will determine on average once you're an adult are you a morning type or are you an evening type”

“is somewhere between 25 to 30 percent of the population or morning types 25 to 30 or evening types and then the rest of us are somewhere in between”

“And by the way, it's genetic. You don't get to decide whether you're a morning type or an evening type. It's hardwired into your genes. We know the genes. It's not your fault.”

“And I think the data are that, you know, some...it's roughly a third, a third, a third. A third-ish of people are morning people,”

“What's the difference...like, chronic insomnia, like, people that actually have insomnia versus someone who has a chronotype, someone who has a genetic predisposition to being like a night owl, where they stay up really late and then, like, sleep, like, most of the day? Like, there are people that just genetically are predisposed to that.”

“A third-ish of people are morning people, a third-ish of people are evening people, and then a third-ish are somewhere in the middle.”