Getting a good night’s sleep
Humans, along with our closest great-ape relatives, are rather unusual among the animal kingdom for our habit of getting a good night’s sleep. While most mammals grab snatches of shut-eye as and when they can, we do it in a single long, continuous stretch, every night. But we are not alone.
Biologists have found that another, distantly-related, primate gets all its daily sleep in one go, too – albeit during the daytime.
“So far, it has been common to believe that this rhythm of sleep arose when our primate ancestors switched from being nocturnal to being dayactive,” says Kathleen Reinhardt of Oxford Brookes University.
It has also been suspected that the deeper sleep this afforded set the scene for the apes’ leap in intelligence.
But the discovery that the Javan slow loris sleeps continuously during the day casts doubt on all that, and not only because it is nocturnal.
“The lorises belong to a very old group,” says Reinhardt. “The special rhythm of sleep that characterises man and many of our closest primate relatives seems to be a much older trait than previously thought.”
Slow lorises sleep clinging to a branch, and their limbs are designed to hold on effortlessly for long periods. Stuart Blackman
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