While I haven't done extensive historical research on sleep habits, the limited history that I have read makes me doubt your assertion. I think being up for a

While I haven't done extensive historical research on sleep habits, the limited history that I have read makes me doubt your assertion. I think being up for a bit during the night and siesta are both things that can potentially happen while keeping a healthy circadian rhythm, but I don't think they are necessary for a healthy circadian rhythm. My impression is that siesta is a very common human practice with a boiological basis, but I'm not convinced that the same is the case with being awake for a while at night. I suspect the human body can adapt to many different schedules and some will work better than others for each individual. My sense is that the most important thing is keeping a very regular schedule to make sure that when we are sleeping we are fully asleep. For me being awake at night seems to independently cause trouble and I suspsect this is likely true of most people, but it might not be the case with everyone. Even so, I suspect an irregular sleep schedule is much worse than being awake at night.