Analysing compiled studies on sleep patterns in 83 species of mammals with the help of statistical techniques, scientists at the Max Planck Institute for Ornithology in Starnberg, Germany, have come to the conclusion that animals with big brains for their body size need a significantly higher percentage of REM (rapid eye movement) sleep, which plays a role in intelligence and cognitive function.
Several lab studies on humans have already suggested that a good night's sleep with plenty in the REM phase, during which the brain is highly active, can improve people's ability to remember what they have learned in the day by about 15 per cent.
AdvertisementJohn Lesku, who led the latest sleep pattern study at the Max Planck Institute for Ornithology, says that he and his colleagues have also observed that species with high metabolic rates for their size needed less non-REM sleep, which suggests that they do not sleep to conserve energy.
He says that animals with high metabolic rates may, instead, sleep less because they burn more calories, and have to spend more time foraging for food.
The researcher says that this finding contradicts previous studies that suggested that animals with a relatively high metabolic rate for their body size seem to need more non-REM sleep, as it helps them conserve precious energy.
"It's to emphasise the necessity for these kinds of research. Evolution does matter," New Scientist magazine quoted him as saying.
Lesku's point of view is supported by another study by Isabella Capellini of Durham University in the UK, who has also tested the strength of the influence that evolutionary relatedness has on sleep patterns.
"Sleep scientists have ignored the fact that sleep could be affected by evolutionary relationships. But it's the strongest possible signal," she said.
After taking evolution into account, Capellini's team found that ecological factors are more important than previously acknowledged.
One of her team's findings was that species at risk of predation tended to sleep less.
"Prey can't afford to sleep for longer. This indicates that if they still sleep at all, it must do something important," she said.
Lesku's findings appear in the journal Sleep Medicine Reviews.
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