> […] why we still sleep. Why hasn't this evolved yet? A number of animals can put one half of the brain to sleep while the other half remains alert¹. As for

> […] why we still sleep. Why hasn't this evolved yet? A number of animals can put one half of the brain to sleep while the other half remains alert¹. As for eliminating sleep or shortening it; for such “trait” to evolve there would (beyond being physically possible and the proper mutations having occurred) need to be an advantage that would cause more individuals with the trait to survive (and pass on their genes). Considering that we have been sleeping in trees and caves, and in groups, there’s probably not a significant larger chance of someone requiring less sleep to make it through the night. ¹ http://en.wikipedia.org/wiki/Unihemispheric_slow-wave_sleep http://en.wikipedia.org/wiki/Unihemispheric_slow-wave_sleep