Night people and morning people tend to be found in different professions, with, say, musicians tending to be night people and business managers tending to be morning people. I'd never seen, however, any data on how the distribution of night and morning people differs by nationality or ethnicity.
I wonder how heritable it is? My guess would be that it's one of those traits, like handedness, that are only mildly heritable.
My supposition would be that this would be one of those traits you'd want widely widely varying among your relatives. In caveman days, when keeping a fire going could me a matter of life or death, you'd want some members of your clan to wake up early and be rarin' to go collect firewood and get the day started, while you'd want others who naturally stayed up late and made sure the fire didn't go out. But geneticists tend to scoff at my idea that there could be selection for variation.
The only evidence I've seen of national variations in night and morningness is in E.T. Bell's famous 1936 book Men of Mathematics: The Lives and Achievements of the Great Mathematicians from Zeno to Poincare. Bell, a fan of Sir Francis Galton, was interested in a lot of questions that are considered improper today. The chapter on Poincare discusses a 1902 survey of 100 mathematicians that asked them 30 questions about how they worked.
"Again, anyone with mathematical friends will have noticed that some like to work early in the morning ... while others do nothing till after dark. The replies on this point indicated a curious trend -- possibly significant, although there are numerous exceptions: mathematicians of the northern races prefer to work at night; while the Latins prefer the morning."That's the reverse of the stereotype of Latins who stay up late because they take a siesta during the hot afternoons. Perhaps mathematicians tend to be out of sync with their societies?