Get­ting a good night’s sleep

BBC Wildlife Magazine - - WILD NEWS -

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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