But I’m Not Sleepy!

Here’s the second Psychology Today blog post:

One of my strongest memories from high school is the feeling of that extra hour of sleep when we fall back into standard time each autumn. After the first few weeks of school, and the mounting sleep debt of having to wake up at too early of an hour, having that extra hour of sleep felt exquisite. But the eventual transition back to Daylight Saving Time in the spring was excruciating. Losing that hour of sleep made school much more difficult – at least until my urge to sleep aligned with Daylight Saving Time. My circadian rhythm was generally not the same as the one that I needed to get through the school day without feeling sleepy. This situation made very apparent to me that it’s arbitrary when we start school and work, and that my need for sleep was often at odds with those decisions.

Our circadian rhythms are the result of complex interactions between our body and our environment, and are generally seen as the force that cues us to feel sleepy. On one side, we have the urge to be awake. On the other, the need to sleep. When one overtakes the other, sleep or wakefulness ensues. As we sleep, the need to sleep reduces, and our alerting functions take over – until the need for sleep builds up again and we head for bed. Scientists have suggested that circadian rhythms govern much more than our need for sleep, including our urge to defecate and our appetites. We can delay our need for sleep – or eating or defecating – temporarily, but we can’t defer it indefinitely.

In his book, The Promise of Sleep, William Dement recounts the case of Randy Gardner who stayed awake for eleven days – but we now know that anyone who stays up for too long starts to microsleep as their need for sleep forces them to rest, even while their eyes might be open. As much as we might fight it, our circadian rhythm shapes our sleep.

Many people would tell you that our circadian rhythms are innately tied to the environments we’ve evolved in, but that’s not strictly true. Over the millennia that humans have evolved, they’ve inhabited a number of diverse environments around the globe, all with their own light cues – in circumpolar regions, humans have lived in periods of prolonged night and day; in equatorial regions, humans have been exposed to roughly equal periods of night and day. Sleep, in both of these environments – and all of the environments in-between – has developed as both a social and biological response to these cues. We sleep when we’re tired, but we also tend to take to our beds when the nights are long and we have limited light and heat. This has resulted in a wide variety of sleeping schedules – from societies that favor a midday nap to those that favor a long night in bed. And, then there’s the United States, that tends to favor a short night in bed – eight hours or less – and no midday nap, except for the very young and the very old.

If you were to measure the circadian rhythms of people throughout the world, you should find that there are a wide variety of expressions of circadian cues. But when we look at the science of sleep, one representation of circadian rhythms prevails, and it often looks like this – which I’ve borrowed from Dement’s Promise of Sleep, and which I talk about extensively in my book, The Slumbering Masses:

This model is based on individuals sleeping for eight hours at night – from 10 p.m. until 6 a.m. But what if that individual took a nap in the middle of the day? Her sleep need would decrease accordingly and start to rise again. At bedtime, her sleep need would be less, but still enough to get to sleep. Or, if she slept in two four-hour blocks throughout the day, the need would be more balanced, and never so great that her urge overtakes her need – she wouldn’t just spontaneously fall asleep while in a meeting or driving home.

If we consistently slept in different patterns, our circadian rhythms would look quite different – both because of how we slept, but also because of other environmental cues, like food and light. Humans have evolved to have flexible circadian rhythms, and beyond just patterning of sleep shaping our rhythms, our exposure to light and our consumption of food shape our urges for sleep. This is one of the keys to understanding jetlag: when we go from one set of environmental cues to another, our bodies often react negatively, with our cues for sleep being mismatched to environmental cues. Only after we adjust to the new patterning of light and food intake do we begin to adjust to the new time zone, and our sleep follows suit. This can take a while, in part because our adjustment to food intake can be rather slow, whereas light impacts us quite quickly. Adjusting to Daylight Saving Time is often no big deal, because it’s a slight variance in time and we adjust our schedules accordingly. But adjusting to a bigger time difference – a few hours or more – can often leave us with a serve sense of being dislocated in time.

Despite the relative flexibility and variation of circadian rhythms, the models we have of our biological cues are fairly rigid and are based on the assumption of nightly consolidated sleep and large meals throughout the day. If we slept in two four-hour blocks, or one nightly block supplemented with a daily nap, our rhythms would alter. If we ate smaller meals throughout the day as well, our rhythms would again look less dramatic in their highs and lows. But such an organization of sleep and eating would depend on us investing in a much different ordering of society. The result would both be a dramatically different experience of sleep for us – as individuals and as members of society. And it would change how we conceive of normal and pathological sleep. What we now think of as sleep disorders – narcolepsy, insomnia, shift work sleep disorder – might not be so pernicious and in need of medical treatment.

But changing society to ease our discomforts around sleep seems unlikely – if it’s ever going to happen, it’s going to depend on denaturalizing our conceptions of human circadian rhythms and to take seriously how other orderings or society might benefit our biological experiences of ourselves and the world.

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.