# s-behav: two (multi?) step sleeper

A. Roger  Ekirch. Segmented  Sleep  in  Preindustrial  Societies. Sleep. Volume 39,  Issue  03. Letters To The Editor. http://dx.doi.org/10.5665/sleep.5558

http://journalsleep.org/ViewAbstract.aspx?pid=30498.

Bora Zivkovic. What is a `natural' sleep pattern? December 5, 2011

http://blogs.scientificamerican.com/a-blog-around-the-clock/what-is-a-natural-sleep-pattern/    

http://blogs.scientificamerican.com/a-blog-around-the-clock/2011/08/29/everything-you-always-wanted-to-know-about-sleep-but-were-too-afraid-to-ask/

Richard A. Friedman. Sleep  Disorder?  Wake  Up  and  Smell  the  Savanna. March  14,  2006

http://www.nytimes.com/2006/03/14/health/14beha.html

http://circadiana.blogspot.com/2006/03/what-is-natural-sleep-pattern.html