I know that girls can all get on the same menstrual cycle when they spend enough time together. They all end up following the alpha female's cycle. I wonder if it's the same with sleep...the old people had the stronger circadian rhythm (perhaps because we were in their environment) and it kind of rubbed off on us. Another idea I have is that there wasn't much to do and we were trying to be quiet, so it's easiest to go to bed.
I think the stronger circadian rhythm theory gets some other support from when I go visit my immediate family and my mom ends up staying awake later than usual when I'm home. Part of it may be that she wants to catch up with me but it might also be that my presence influences her sleep routine. Does anyone know of any studies done on this? Anybody have personal experience?