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Figure 1.
Sleep durations in
representative mammals. Daily REM sleep time in mammals does not
positively correlate with encephalization. The highest levels of REM
sleep are seen in the platypus and the lowest in the dolphin. Despite
our unique learning capabilities, human REM and non-REM sleep
parameters are not unusual and are in accord with our size and level of
maturity at birth relative to other mammalian species. Number of hours
of REM sleep and total sleep across the 24-hour cycle are listed for
each animal pictured (36, 37). [Photo credits: platypus,
Tom McHugh/Photo Researchers; opossum (photo is of a
Virginia opossum), Alden M. Johnson, California
Academy of Sciences; ferret (photo is of a black-footed ferret), © D. Robert Franz/CORBIS; big brown bat, © 1997 Merlin Tuttle, from
Bats: Shadows in the Night, used by permission of Crown
Children's Books; hedgehog, Maurizio Lanini/CORBIS; armadillo, John
and Karen Hollingsworth/U.S. Fish and Wildlife Service; human,
Kristi Alderman; guinea pig, Animals Animals; guinea baboon, Mickey
Gibson/Animals Animals; sheep, Barbara Wright/Animals Animals; horse,
Lucie R. Alderman; giraffe, Arthur J. Emmrich, California Academy of
Sciences; dolphin, Gerard Lacz/Animals Animals]
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