Boyd Eaton and his students did some of this work. Its touched on in The Paleolithic Prescription (popular book) with more details in papers before and since (search on book's authors' names for research papers. Sorry I don't have better for you now.) As I recall they identified three sleep patterns from anthropological studies of populations not influenced by modern technologies (eg. electric lighting) and from historical documents (ex. Victorian era doctors' notes mentioning what were considered normal sleep patterns at the time.)
1) Early to sleep + early to rise
2) Late to sleep + late to rise
3) Late to sleep + late to rise (with waking in the middle of the night)
A modern cartoon characterization of type three is Dagwood Bumstead from the comic strip Blondie. He would get up naturally for midnight snacks and over-sleep for work or snooze during work. Type three Victorians were noted by their physicials as naturally rising for midnight prayers or sex with spouses.
As to genetic selection, the postulated survival advantage relates to the military three watches of the night. With group members naturally awake throughout the night predators were better protected against, surprise attacks less likely, etc.. Hence, a mixed group consisting of all three types would have a survival advantage.
A modern cartoon characterization of type three is Dagwood Bumstead from the comic strip Blondie. He would get up naturally for midnight snacks and over-sleep for work or snooze during work. Type three Victorians were noted by their physicials as naturally rising for midnight prayers or sex with spouses.
As to genetic selection, the postulated survival advantage relates to the military three watches of the night. With group members naturally awake throughout the night predators were better protected against, surprise attacks less likely, etc.. Hence, a mixed group consisting of all three types would have a survival advantage.