See “Internal Time” by Till Roenneberg, which is a very accessible book by a researcher in this field. If I remember correctly, the book gives some good eviden

See “Internal Time” by Till Roenneberg, which is a very accessible book by a researcher in this field. If I remember correctly, the book gives some good evidence of a potential genetic basis for chronotypes, although not to the level of identify particular genes. Your case may be a bit extreme, but certainly describes me in my early 20s (not coincidentally, also the peak years of night owlism). But there are much moderate Night owl/lark situations. My kids school starts at 8a. Some in our area start at 720a. In order to reliably get my (young) children to school on time, I need to be up by 645a. This means my absolute last moment to be asleep for 8h of sleep is 1045p. No matter when I climb into bed, I have trouble managing to fall asleep by them, and I’m regularly in bed before 10p, and I have data from various fitness trackers to back this up. 1115-1130 is really the norm. Which is a long way of saying that there are definitely people with strong, biological driven sleep preferences. Modern screens and lights can exacerbate these tendencies, but assuming that people can just “fix themselves” ignores the body of evidence.