Today.Az » Weird / Interesting » Apes reveal secrets to good sleep
20 April 2015 [15:22] - Today.Az
Watching an orangutan sleep is like watching a giant, orange baby slumbering sweetly.
huge great apes like to get into bed, and nestle down for a long and
deep night’s sleep, their eyes occasionally dancing behind their
eyelids, perhaps dreaming a fleeting orangutan’s dream.
Watching a baboon sleep is more like watching a small bitter paranoid person desperately trying to get some shut eye.
They sleep badly; sitting upright, balancing on their bottoms, minds
whirring, constantly fearful that something or someone is after them.
begs an important question: why does an orangutan sleep so soundly,
whereas its primate relative, the baboon, suffers a fretful night’s
The answers, scientists are learning, are rooted deep in our
evolutionary history. They help explain, in part, how great apes
including humans were able to evolve into the beings we are today, and
also why humans routinely prefer to sleep in beds.
“Sleep has only recently been acknowledged as a potentially critical factor in human evolution,” says anthropologist David Samson of Duke University in Durham, North Carolina, in the US.
Yet scientists have rarely studied how sleep may have affected our development as a species.
So Dr Samson and colleague Robert Shumaker of Indiana University in Bloomington, in the US, decided to do just that.
They chose two primate species to study, publishing the results in the American Journal of Physical Anthropology.
“We chose orangutans because they were a species of ape that had yet
to be studied by sleep scientists,” Dr Samson told BBC Earth.
they are the most distantly related great ape to humans, and therefore
are an important species to generate comparative data.”
baboons were chosen specifically due to their being one of the largest
bodied monkeys that do not use sleeping platforms. Essentially, I wanted
to control for body size and ask the question: why do both these
large-bodied primates differ so remarkably in their sleep behaviours?”
The scientists videoed five orangutans and 12 baboons sleeping in captivity over periods of one to four months.
They confirmed that the orangutans slept for longer, and more deeply
than the baboons, suggesting that all great apes do indeed sleep better
“We discovered that by every measure of sleep
quality, orangutans are the ‘better’ sleepers; that is, compared to
baboons, orangutan sleep is deeper, longer in duration, and less
fragmented,” says Dr Samson.
Why they do so is even more revealing.
date, every population of wild great ape studied builds platforms to
sleep on. Gorillas, orangutans, chimps and bonobos create nesting
platforms in the trees, whereas modern humans construct beds to lie on.
But every other type of primate does not sleep this way.
the smaller apes, do not construct sleeping platforms, nor do any large
monkeys such as baboons. Most monkeys actually sleep sitting in the
trees, balancing on a branch, often upright, resting upon their bottoms.
And that difference in sleeping style explains how well they sleep.
The orangutans studied liked to relax, lying down, sleeping on their
front and back. “The baboons spent most of their time sleeping while
sitting up in a guarded position,” says Dr Samson. When baboons rest
this way, they often sit upon thick, pink patches of hard skin, called
ischial callosities, which shape their buttocks.
This difference in sleeping style may have played a fundamental role in the evolution of great apes, including humans.
Around 14-18 million years ago, the common ancestor of great apes is
thought to have switched from sleeping on tree branches to within
specially constructed sleeping platforms.
“I don’t believe the first platform-constructing ape thought they would have a better night’s sleep,” says Dr Samson.
throughout the Miocene (an epoch lasting from 23 to 5 million years
ago), apes were growing bigger. They likely started building sleeping
platforms to support their size and weight.
allowed apes with large mass to sleep securely in the trees, bypassing
predators and blood sucking insects,” explains Dr Samson.
conducted previous research suggesting that all primates weighing more
than 30kg likely needed to build a bed in the trees, sleeping in such
And sleeping in beds confers another significant evolutionary advantage,
it allows apes to sleep more deeply, getting more deep, nonrapid eye
movement (NREM), sleep.
“This ‘better’ sleep could have positively affected cognitive
ability,” says Dr Samson, perhaps improving the consolidation of
memories, for example.
“Sleep quality may be a critical difference
between apes and monkeys. Monkeys likely spend more time in ‘light’
sleep due to their less comfortable, less secure, and socially dynamic
sleep environments. The trade-off is that they can easily arouse from
sleep when a predator is around, or a social partner is active, but the
cost is that they don’t achieve the benefits of deep sleep.”
“We apes seem to have innovated an effective way to sleep both securely and comfortably.”
an evolutionary perspective, just as the transition from tree branches
to sleeping platforms had adaptive benefits, so too did the early
hominin transition from sleeping platforms to secure ground sleep."
later transition, to sleeping on the ground, and later in beds, could
have given early humans a competitive advantage over other species, he