Some months ago, I found a video about chronotypes. I don’t know how much of it can be considered scientific, but the websites have some interesting statistics about the number of people that fit in each of the categories. Apparently, only a minority is an early-bird or lion-type or morning-person. It has some associated traits that may explain why that schedule prevails (extraversion, leadership, good health), but it is unhealthy and unproductive for the rest! It’s not okay.