Is there any science that suggests that people are hard-wired to be "early" or "late" people, and that there's just nothing one can do to change it? Legitimately curious. To me "I'm just not a morning person" seems like a pretty weak excuse for not being able to function as a professional because it's a little early in the morning, but maybe it's been shown that this is some intrinsic genetic trait that you can't control...?
It would be extremely unusual if all people had exactly the same circadian rhythm; some variation in sleep-wake cycles between individuals would be expected in the same way as a variation in height would be expected.
Wikipedia [1] says: "Normal variation in chronotype encompasses sleep–wake cycles that are from about two hours earlier to about two hours later than average." (Unfortunately the citation link is broken.)
