Well what about the siesta? Or, before lighting, people more commonly had segmented sleep. http://en.wikipedia.org/wiki/Segmented_sleep http://en.wikipedia.org/

Well what about the siesta? Or, before lighting, people more commonly had segmented sleep. http://en.wikipedia.org/wiki/Segmented_sleep http://en.wikipedia.org/wiki/Segmented_sleep This seems to be a modern, social issue, not so much a physical one.