I'm almost positive that's bullshit because I spent half of my life as a "night owl", convinced it was just something inherent to me. After my wife took a job that had her waking up at 4am, and the requisite adjustments to her bedtime, I found myself totally fine with going to sleep at 10am or earlier everyday.

In a lot of ways an early bedtime, or an average bedtime, is preferable to staying up to the wee hours, but given the context I couldn't see the benefits until I had experienced it myself for a few months. So in my opinion, if there is some kind of genetic marker for chronatype, it's either not very influential, only expressed in a subset of the populace or largely BS.

I buy that it might be A Thing but have a strong suspicion that 90+% of modern "night people" are just addicted to the 24/7 casino-bright circus that is modern home entertainment and nighttime lighting (as most of us are) and would stop being "night people" if you took that away.