Why Being a Night Owl is Genetic

A theory I have on why Night Owls can't sleep is that our ancestors had people in the night to watch over and protect the tribe or village while the others were sleeping. The Night Owls would sleep during the daytime when the Early Birds were awake to take care of the village. This has brought me to the conclusion that this may be a genetic rather than it being nurtured into us.

Another theory of mine is that our ancestors may have been from a different timezone but I think this theory is less likely.