If you ever find yourself wondering about just how big a difference a comfortable bed can make in your life, you might want to give consideration to a study that was recently conducted by anthropologist David Samson of Duke University and Robert Shumaker of Indiana University in Bloomington. The two colleagues set out to investigate exactly why some of our primate relatives sleep soundly through the night, while others sleep fitfully and restlessly.
It’s probably not something that you were aware of, but orgutans – our giant orange cousins that have become so well loved for their playful antics and soulful expressions, sleep comfortably nestled into nests that they build, while baboons and other monkeys sleep badly, and sitting upright. Observing the two is akin to watching a person sleeping soundly versus watching an insomniac or person suffering from sleep apnea struggling through the course of the night. The researchers have learned through observation and study that the difference between the two has a great deal of impact on the different ways that our ancestors evolved, with the fact of sleeping in a bed playing an important role in the advances that humans and other apes made.
According to Samson, “Sleep has only recently been acknowledged as a potentially critical factor in human evolution.” That is why the two scientists decided to pursue the study, which was just published 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. Furthermore, they are the most distantly related great ape to humans, and therefore are an important species to generate comparative data. The 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 behaviors?”
In order to conduct the study, the pair observed and recorded the sleep habits of 12 baboons and 5 orangutans as they slept in captivity. The animals were studied over periods of one month to four months, with the scientists tracking the positions that they slept in, what movements they made during the course of the night, what their sleep quality and cycles were, and how much time they spent waking and sleeping. Rapid Eye Movement activity versus nonrapid eye movement was measured to monitor brain activity during rest and to distinguish light sleep versus deep sleep.
What their observations revealed was that when compared to the baboons, the orangutans slept much better and more deeply, and for longer periods of time. “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,” Samson said. Perhaps more telling was the reason behind the vast difference. The scientists observed that all great apes in the wild build sleeping platforms which are primitive versions of beds. These include orangutans, as well as gorillas, chimps and bonobos. These platforms are located in the trees. Other primates do not build these structures. Gibbons, baboons, and most monkeys spend their rest time sitting upright in the branches of trees, balancing precariously and sitting on their rears. This provides an obvious reason behind the difference in the sleep quality between the species. Where the apes are able to fully relax while resting, “The baboons spent most of their time sleeping while sitting up in a guarded position,” explains Samson. The pressure that this effort places on their bodies is responsible for the distinctive callouses of hard skin that appear on the animals’ hind quarters. More importantly, the anthropologists are theorizing that the difference in sleep style is an integral part of the way that the apes, and humans, developed.
He indicates that this switch from sleeping on tree branches to sleeping on platforms occurred roughly 14 to 18 million years ago. Dr. Samson does not believe that the switch came in a search for better sleep as much as to accommodate the animals’ rapidly increasing body size. The platforms that they built were designed to support them. “Sleeping platforms allowed apes with large mass to sleep securely in the trees, bypassing predators and blood sucking insects,” he says. His previous research points to evidence that once a primate species evolved to sizes that exceeded more than 30 kilos in weight, they tended to begin building platform beds, and that the switch also happened to provide them with deeper sleep. “This ‘better’ sleep could have positively affected cognitive ability,” says Samson, and may have led to the difference in the various species’ ability to learn and consolidate memories.
“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. From 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.”
Though the shift in sleeping quarters may have been a necessity born of the need for support and comfort for a growing body, the resulting increase in rest and deep sleep may have been what enabled our ancestors to succeed and develop the cognitive abilities to create tools and to survive against challenges they faced in the elements. Today’s humans, who so frequently set sleep aside as a low priority, might take a lesson from them.