Of Bonobos, Chimps and the Evolution of Sleep
Radically Novel Dilemmas
Our closest living relatives in the animal kingdom are chimpanzees and bonobos. We share 99.6% of our DNA with these animals and, while we’re highly genetically related, our behavior is vastly different. For example, bonobos are more playful than chimps, chimp infants don’t cry (like human infants), and humans drive cars and construct philosophies to explain the world and human behavior. Also, bonobos and chimps are mostly arboreal—that is they spend a lot of time in trees, especially during sleep, while we humans are ground bound.
In my own cerebral human moment the other night (laying in bed, of course), I started wondering how our close animal relatives sleep, and more specifically where do they sleep their infants? I see a lot of sleep information on the internet about the best way to sleep babies/kids (sleep training vs. responsive parenting vs. bedsharing) and I just wanted to know what the other apes do without so many expert opinions, emotions, righteousness, or online commenting.
I turned to a 2016 paper from Evolution, Medicine, & Public Health to get an idea of how we and other primates evolved to sleep. Most primates used to sleep in trees (on branches and such) until they got so big that they started falling out and getting injured and dying.
A big evolutionary transition occurred when our great ape ancestors started building strong, platform nests to sleep on. Each night, stable and strong trees are selected, and platforms are built for sleep, with each individual building a separate sleeping nest—except for the dependent young who sleep with a caregiver. Recent research shows that the better the sleeping platform quality, the better the sleep quality, which translates into enhanced brain function and higher intelligence.
While most of the other apes continued sleeping in their cozy tree nests—to avoid predators and for the pleasant decrease in insect bites—our human ancestors moved to sleeping on the ground. We are also the shortest sleeping primates with the highest percentage of rapid eye movement (REM).
In discussing where human infants sleep, the authors of the paper stated, “All discussions of co-sleeping should begin by appreciating how radically novel it is for dependent children to even have the option to sleep separately from caregivers.” It is only with the option for independent, safe, and modern living conditions that we have a dilemma involving infant-parent co-sleeping. We really know how to create our own unique human problems and then capitalize on those problems!
Bedsharing is either vehemently opposed and recommended against or supported as a peaceful and harmonious practice. Many people have opinions on this subject, but what I find interesting is that while sharing a sleeping space is evolutionarily normal, a proposed reason that infants seek closeness, frequent feeding and crying at night is because it tends to increase inter-birth intervals.
In other words, babies want to feed often and sleep close to their mothers so another baby doesn’t come along too soon and steal their resources. This, the authors say, suggests that there’s substantial parent-offspring conflict even within the context of sleep.
What struck me in this paper was the phrase, “radically novel.” The modern environmental and social conditions we’re living in introduce a multitude of parenting (and other) dilemmas that wouldn’t exist to stress us out if we still lived like our closest animal relatives.
And, when it comes to sleep, the pre-conceived expectations of infant sleep paired with the Western obsession with independent sleep tend to create a nighttime battle where the parents are expected to “fix” or “train” their children who are expressing biologically normal sleep needs, like the need for comfort, feeding, or contact. This isn’t to say these biologically needs are easy to attend to (see parent-offsping conflict above), just that they are normal.
Evolutionary information is often conflated to morality, or as a right or wrong way of being or living. What it really gives us is proposed information about past contexts and conditions that shaped our physiology and behavior that may allow us to understand, or look at, our present context differently. Then, we have to take into account our modern, unique, individual ecological contexts including our family structure, preferences, environment and the norms of our culture.
After shifting through all of this information, we get to make a choice. Because, for all of the radically novel dilemmas of our time, one thing we do that our closest animal relatives don’t is choose what feels right for us.