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Humans need less sleep than other mammals, and that sleep has better results, according to a new study. Researchers at Duke University put together information on the sleep habits of hundreds of mammals, including 21 primate species. They found that humans need less sleep than chimps, macaques and lemurs. Humans spend a greater part of sleep in deep stages that help the brain restore itself. The study also found that a human’s sleep is higher quality. A deep stage of sleep, called rapid eye movement, or REM, makes up 25 percent of a human’s sleep. In primates like lemurs or monkeys, REM sleep is less than 5 percent. David Samson, the study’s co-author said the shorter, higher quality sleep make humans special. Samson’s research team found that humans can do well with about seven hours of sleep a day. Other primates need as many as 14 to 17 hours of sleep. Samson said human sleep habits started changing during prehistoric times. Human ancestors moved from sleeping in trees to sleeping on the ground. Better sleeping habits meant better sleep in a shorter amount of time. Our ancestors slept near fire and in large groups for warmth and safety. This could have allowed them to get the most out of their sleep in the shortest amount of time. That left more time for other activities, like learning new skills. The study also notes that humans spend about one-third of their lifespan sleeping.