The New York Times took on this topic a few years back in a very good article that argued that the whole idea of the 8-hour sleep was invented by the mattress industry (and other purveyors of sleep products), and that humans don't need anywhere near 8 hours of continuous sleep.

Ironically, all of the industry's marketing makes people anxious about getting enough sleep--and makes it harder for them to get to sleep (thus propagating the need for more expensive mattresses and pillows.)

http://www.nytimes.com/2007/11/18/magazine/18sleep-t.html?pa...