Great apes like orangutans, gorillas and chimpanzees all like to curl up to sleep. Humans, too. Apes are famous for making comfy beds of branches and leaves; other primates, with the exception of lemurs and lorisids, don’t build such nests. And even those lemurs and lorisids primarily use tree holes to rear their young, rather than building new beds in different sites. For BBC Earth, Matt Walker explains further differences the sleeping habits of apes (like orangutans) and monkeys (like baboons):
These 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.
Like many distinct differences between apes and other primates, this sleeping behavior has attracted the attention of researchers hoping to understand how humans and apes have evolved to be so intelligent. We know, for example, that chimpanzees are remarkably selective about where they nest. Now, researchers based at Duke University and Indiana University recently watched orangutans and baboons sleeping in captivity in an attempt to learn more.
The orangutans slept longer and deeper than the baboons, they reported in the American Journal of Physical Anthropology. “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,” David Samson of Duke University told BBC Earth.
Since sleeping in constructed beds is common to great apes, the practice likely first appeared in the group’s common ancestor, around 14 to 18 million years ago. "Sleeping platforms allowed apes with large mass to sleep securely in the trees, bypassing predators and blood sucking insects,” says Samson. Research in chimpanzees agrees that sleeping in tree platforms keeps the apes safer and helps them escape uncomfortable humidity.
The longer sleep may also have been key to the development of larger brains. Samson adds, "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."