Humans, then, seem to have evolved to need less sleep than our primate relatives. Samson showed in a 2018 analysis that we did this by lopping off non-REM time. REM is the sleep phase most associated with vivid dreaming. That means, assuming other primates dream similarly, we may spend a larger proportion of our night dreaming than they do. We"re also flexible about when we get those hours of shut-eye. (Read about the lost medieval habit of biphasic sleep.)