When my boyfriend and I moved in together, he took the left side of the bed, and I took the right. There was no negotiation or conversation; it just happened that way. Now, even on nights when he's out of town, and the bed is all mine, I nevertheless sleep on the right side. A habit certainly promoted by preferred pillows and individualized nightstands (mine is piled high with books and notepads, while my boyfriend's is littered with outdoor magazines), couples divvying up their beds is likely more of the rule than the exception. So I wondered, as I do with pretty much every kneejerk-y relationship pattern, is there any science behind it?
When it comes to basic bed positioning, people appear to have some shared predispositions. A 2010 study published in Evolutionary Psychology found people favor sleeping within full view of the bedroom door and windows. For probably self-protective reasons, study participants also opted for the bed to be as far away from the bedroom door as possible, as long as it still faced the door.
Research on why we sleep on certain sides of the bed is harder to come by, aside from a highly publicized survey of people's self-reported bed side preference and levels of life and career satisfaction (always remember: let correlation vs. causation be your guide). In his book Two in a Bed: The Social System of Couple Bed Sharing, Paul C. Rosenblatt interviewed a number of couples about their bed habits and found that couples sleeping on the same respective sides of the bed night after night is nearly universal. He also identified eight primary reasons for bed side preference:
- Old habits: it's the side you slept on before you began sharing a bed.
- Claustrophobia: it's the side away from the wall to prevent feeling trapped.
- Bathroom breaks: it's the side most convenient to the bathroom door.
- Protectiveness: straight men tend to sleep on the side of the bed closest to the bedroom door to be protective of their wives or girlfriends.
- Early birds: whoever gets up earlier in the morning sleeps on the outside.
- Parenting: whomever is on baby or kid duty during the night sleeps on the outside.
- Pain: you pick the side that yields fewer aches and pains.
- Temperature: you pick the side that's warmer.
Now that I think about it, the side of the bed I sleep on predated my relationship. Same thing with my unconscious compulsion for cover-stealing, which I should probably conduct some follow-up research on as well for my boyfriend's sake.