[Supraperplex]

What I have read somewhere a long time ago, is that the chronotypes are actually functions of the inner clock in so much as that you either have an inner clock of a 23 hours day or a 25 hours day. (Compare also to leap year etc)

So this then makes you somebody who tends to wake up earlier each day or later, depending on your inner clock.

I found that explanation more convincing. I am with you, we haven't figured it out yet. But I would say, there is something to it.