Why We're Stuck on a Particular Side of the Bed

In sustainability circles, the concept of habits comes up a lot. Usually, it is in the context of changing the unsustainable ones, like breaking up with single-use water bottles or ditching coffee pods for more eco-friendly options.

Understanding one's habits in general can be an important part of becoming more sustainable. So, let's look at one of life's more enduring habits: what side of the bed you sleep on. While this may not have a sustainability side, so to speak, the psychology of habits is fascinating and can play a big role in one's personal carbon footprint.

In terms of bed sides, no matter how hard you might try to change it up, maybe even switching sides every other night, you eventually pick a side—and stick with it.

And why not?

You've got everything just right on your side of the bed. The night lamp, for instance, has become an instinctive reach. You can turn off your alarm without opening your eyes. That half-eaten snack is still waiting patiently for a late-night nibble. And let the crumbs fall where they may—it's your side of the bed!

In time, you've tailored your side of the bed to your specific needs. Why learn new behaviors every other night? It can be jarring to reset your habits just after you've established a system.

However, in this case, breaking the habit may be more challenging. Fortunately, you may not have a reason to change this one, but still.

Exactly why we choose a particular side to set up camp in for a third of our lives is a little more complicated. Like evolutionary psychology complicated.

There's surprisingly scant research on the specifics of sleep sides. One major study published a while back, however, suggests we position the entire bed based on primal fear.

The University of Munich researchers found that "people prefer sleeping places that allow them to view the entrances to the sleeping room (doors and windows) from a distance while remaining concealed from the entrances themselves."

The fear of predation, even in coddled suburban homes of the 21st century, still looms so large that participants in the study overwhelmingly positioned their beds as far from the door as possible.

But what about divisions in the bed? Do we instinctively pick the side that's farthest from the door—even if we share the bed with someone else?

That's an even murkier research subject. Paul C. Rosenblatt, a professor at the University of Minnesota, came up with several factors in his 2012 book, called "Two in a Bed: The Social System of Couple Bed Sharing."

We may, for example, enjoy the morning sun that streams in from the window—more so than our partner who hates the light, craving only darkness. Bathroom proximity, even if it only saves a couple of steps, may also be a factor. For frequent tinklers, those steps add up. Rosenblatt suggests another, somewhat more noble reason for our choice in bed real estate. Men may sleep on the side of the bed nearest the door to guard their partners, even in sleep.

A 2011 poll goes so far as to suggest the left side of the bed is a happier place. For the survey—sponsored by a hotel chain—3,000 adults were asked about their happiness at home and work, and of course, what side of the bed they slept on.

The happiest and most well-adjusted participants reported that they owned the left side of the bed (as determined by facing the bed, not being in it). The researchers also noted that most of these "generally more cheerful" sleepers refused to swap sides with righties. There's a limit, apparently, even to love.

But it's important to note the poll doesn't make it clear that the left side of the bed made people happier, or if happier people were just drawn to that side.

At the end of the day (literally), your habitual preference for one side of the bed may not have much impact beyond pillow talk with your partner. But in general, understanding why we do what we do can be an important part of making healthy, sustainable choices—and that's not something to sleep on.