ONE of the most primitive mammals has thrown theories about the evolution of
rapid eye movement sleep into disarray. A controversial new study suggests that
egg-laying echidnas do have REM sleep—but only when the temperature is
just right.
REM sleep remains a mystery. Researchers speculate that it may do anything
from helping consolidate memories during dreaming to mixing up fluid in the
eyeballs to ensure oxygen gets to the cornea.
All birds and placental mammals that have been tested have REM sleep, but
according to several studies, echidnas, whose ancestors split from other mammals
around 120 million years ago,…
