Insomnia? Or Evolution?

Here’s the latest for Psychology Today:

Something woke you up in the middle of the night. The tug of the need to urinate? A bedpartner’s jerky limb? A loud noise? A startling dream? Whatever it was, the event passes as you bring yourself to unsteady consciousness. You lay in the dark for a few minutes — for what seems like a few minutes — deciding whether or not you’re going to get out of bed, if even to go to the bathroom quickly. After another minute of laying in the dark, your bladder has convinced you to go to the bathroom — maybe then you’ll be able to get back to sleep. But once you’re in the bathroom, you know it’s all over. You’re awake. You hadn’t even turned on the lights for fear that doing so would make returning to sleep impossible, but as you fumble in the dark, you know that night has come to an end and your day is starting very early.

The experience is generally referred to as sleep maintenance insomnia. It is characterized by being able to fall asleep when one wants to, but awakening in the middle of the night and being unable to get back to sleep. According to the National Sleep Foundation and drug manufacturers, millions of Americans experience sleep maintenance insomnia on a regular basis. From the perspective of modern science and medicine — and society more generally — this is disorderly sleep. If you wake up after four hours and stay up until the following night, you aren’t getting the amount of sleep you need in order to get through the day. Yet from the perspective of history, being unable to get back to sleep immediately might have everything to do with human evolution.

Humans may have evolved to sleep in a biphasic or non-consolidated fashion, that is, we may be physiologically inclined to sleep in two or more periods over the 24-hour day. We have unambiguous evidence that in pre-industrial Britain and the United States — so before 1840 — that people slept in two periods at night. They would lay down to sleep around sunset or shortly thereafter, wake up around four hours later for a couple of hours, and then sleep again for a few more hours. Today, despite pressures to stop doing so from some quarters, napping cultures thrive in southern Europe, China, Taiwan and elsewhere — people sleep for several hours at night and supplement this sleep with a hefty nap during the day, upwards of two hours.

Sleep is comprised of a series of cycles, which last about two hours for most people. During each cycle, we move through non-Rapid Eye Movement and Rapid Eye Movement (REM) sleep. At the end of each cycle, we move towards wakefulness, and this is when people often wake up. When we wake up in the middle of a cycle — due to an alarm clock or emergency — we often feel terrible throughout the day, struggling with an unresolved sleep cycle. (Incidentally, there are now alarm clocks that detect your progression through a sleep cycle and wake you up at just the right time.) When we think about this from the perspective of evolution, waking up every couple of hours to check your environment is a pretty useful adaptation — sleeping deeply through the night puts one at risk of nocturnal predators. But modern society favors consolidated sleep, so those of us who still sleep as our ancestors did are at risk of being diagnosed with sleep maintenance insomnia.

There aren’t any drawbacks to sleeping in a less consolidated fashion. Some evidence suggests that the grogginess we experience upon awakening is lessened and that we wake up more easily when we sleep for shorter periods. But society is structured around consolidated sleep — as I discuss in The Slumbering Masses, very few employers offer onsite napping facilities — and spending 12 to 14 hours in bed each night would cut into work and family time. And so, even though biphasic sleep might work for us physiologically, it might not work so well socially.

This is why sleep maintenance insomnia is treated as a sleep disorder and not normal human variation: it’s disruptive to society. It can be a nuisance to individuals as well — being chronically sleep-deprived can lead to serious social and health problems — but it wouldn’t be such a nuisance to individuals if society was set up to allow for people to sleep the ways they want to. American sleep patterns are more indebted to our ideas about the workday and school day than any basis in human nature or evolution. Some sleep disorders are serious and benefit from medical attention. But people who experience sleep maintenance insomnia might benefit more from a midday nap than a pharmaceutical fix or a large coffee. It’s up to us all to think about how society might better reflect our needs for sleep — to invent social arrangements that benefit us rather than pharmaceutical companies and the corner Starbucks.

On the Evolution of Sleep

This was originally posted over at the UMN press blog.

Have humans evolved to sleep in a consolidated, nightly fashion, or is this some kind of social construct that we’ve fallen into? There’s a nice write up on the evolution of diurnal behavior in humans by Cris Campbell, in which he uses my recent article in Current Anthropology to think about the relationships between economy, society and sleep. I’m no hardline social constructionist by any means, but I’m sometimes concerned that evolutionary approaches to sleep can be fairly reductive. And one of the dangers of being biologically – and naturally reductive – is that we can come to accept things like American capitalism as the natural outgrowth of a particular pattern of human behavior, which I write about extensively in The Slumbering Masses. Some kind of middle road between biology and society is necessary to really see how sleep is being shaped by social demands and how it impacts our biological well-being. It sounds so reasonable, but it can come across as a little radical when I tell people that there’s no absolute human nature that determines our individual and collective actions, which is the basis of my argument in that Current Anthropology piece.

Rather than thinking of nature and nurture as absolute determinants of our behavior, it’s more appropriate to think of any individual behavior or social form as existing on a continuum between nature and nurture. That is, everything is somewhat natural and somewhat cultural (and sometimes what we say is natural is actually cultural). And sleep is a great example of this: yes, we all have a natural, physiological urge to sleep, but how each person – and each society – organizes sleep varies, based on cultural norms and individual preferences. For some, this can mean nightly, consolidated sleep in an eight-hour chunk; for others, it might mean biphasic sleep – breaking sleep into two (or more) blocks of sleep, arranged throughout the 24-hour day. So our sleep styles may have developed out of evolutionary selection, or it might be a little more complicated.

Biological anthropologists agree that niche construction can often interfere with (for better or worse) the process of evolution. Roughly, they mean that organisms of all sorts (including humans) can change their environments to maximize the possibility of their survival – think beavers building dams, which changes the local ecology both for the beavers, as well as for the other animals, insects and plants that are part of that environment. Humans, the usual argument goes, are niche constructors without parallel, having built complex societies, agricultural infrastructure, and cities. The assumption in much of the niche construction literature is that niches are positive – at least for the constructor. But humans may be able to build niches that are actually unhealthy for us. If humans evolved to be biphasic sleepers, our pattern of consolidated activity throughout the day may be a very good example of a niche gone wrong.

The niche that Americans have built, slowly over the last 200 years, as I talk about in The Slumbering Masses, is one that consolidates our daily activities into one block in the day (say the 9 to 5 work schedule, alongside the 8 to 3 school schedule), followed by a period of recreation – usually taken up by dinner and nightly television – to be followed by our consolidated sleep. All of which begins again the following day, unless it’s the weekend. This kind of niche isn’t a byproduct of some inner nature, but rather a piecemeal construction that we’ve invested in over centuries of social development. And, if we look elsewhere, there are other models – including societies that favor biphasic or daytime sleep.

If we’ve developed a social structure based on our evolutionary desires for sleep, we could expect to generally not feel sleepy throughout the day and rarely see cases of insomnia. Since 30-40% of Americans claim to experience insomnia symptoms with some regularity, and there’s a booming industry in alertness-promoting chemicals (drugs like Provigil, coffee, soda, tea, energy drinks, etc.), it would seem like our niche doesn’t really meet our needs. At its most benign, it might mean that we consume more caffeine than we should; but it might also be that the niche we’ve built is incredibly difficult for many to conform to, leading to experiences of sleep disorders.

There’s at least two dangers in assuming that our contemporary social structure is based on our evolutionary preferences. First, like I mentioned above, it naturalizes things like capitalism as inevitable outcomes of our selected-for behavior, which I discuss in that Current Anthropology article, as well as in The Slumbering Masses. Secondly, it means that disorderly sleepers aren’t just pathological and in need of treatment, but evolutionary aberrations or throwbacks. That might sound a little silly, but similar ideas have been the basis for racism throughout history; as genomics provides a basis for our understandings of ourselves and others, we may also be facing a future of gene-based discrimination, not entirely different from Aldous Huxley’s Brave New World (which I also mention in that Current Anthropology piece).

Now, it may be that through this niche construction, we’re slowly selecting against people who don’t sleep in accordance with it — but with such a large, complex society, that’s unlikely to happen. One of the neurologists I know once said that our brains work best with a cup of coffee in our system. It’s a strange fantasy to imagine that we evolved over time through the selection of individuals who respond well to caffeine. Rather, it’s an accidental correlation between our physiologies and our lifestyles that leads us to really thrive on caffeine (for those of us that do).

It’s a lot safer to recognize that evolution isn’t purposeful in all of its selections; some selections are accidents, although they can be beneficial. What we can select are the social models that govern our lives, and other models are possible, as organizations like the Take Back Your Time movement have advocated for. And what we should be working towards are social forms that meet the needs of all sleepers, not some or even most. Recognizing that society can be different – and more flexible – also accepts that variation within the human species is non-pathological, and that there might be better ways to think about difference than as disorderly.