Good news! Scientists reported last week that women’s backs are different than men’s, and in a way that makes pregnancy plausible for those of us who walk upright. If only I’d known when I was pregnant: I could have crawled less.
As anyone who has ever put on a backpack knows, carrying a heavy load in front of you is hard work, and carrying it in front and down low, say at waist height, is just plain dumb. Sadly, that’s exactly where the package ends up for pregnant, internally-fertilized, live-bearing mammals such as ourselves. Anyone who has experienced the lower-back pain that comes with the third-trimester knows that it’s a design-flaw thing for the uterus to be located anywhere but between your shoulder blades.
You may have noticed that other pregnant animals do not go around leaning backwards, with a paw pressed into the small of the back, and a long-suffering expression. Because they are down on all fours, dogs (for instance) maintain the exact same center of gravity that they had when not pregnant, and while the load is greater, they are not straining to balance it. We, on the other hand, having stood up, are working all the time to balance our weight over our feet. (Those of us wearing Jimmy Choos are working much, much harder.) The curves in our backs (without which there is no “small of the back” — go on, try to find the small of your cat’s back, I can wait) are there because they reduce the strain on bones and muscles of trying to keep from falling over.
Pregnancy, of course, makes the whole problem worse by hanging a weight off the front of the post-hoc, gerrymandered-by-evolution rig that is our back. We compensate by leaning back. But unless you want to fall over backwards, your back muscles have to do extra work to pull your upper body backward while also keeping your lower back and hips in place. Your spine has to stand up to all the pushing and pulling without breaking, or dislocating. You can fairly hear the screaming, can’t you?
Now a group of anthropologists have published a paper in the journal Nature showing that women’s backs are more curved than men’s, thus allowing them to balance that unfortunately-placed pregnancy weight more easily. They also found that women’s back bones are shaped in ways that make them less likely to slip out of place under the strain of pregnancy. In an interview in the New York Times, Dr. Katherine Whitcome, the lead author, suggested that without these changes in women’s backs, our backs would hurt a lot more during pregnancy than they do. One part of me feels grateful for this news. The other part of me feels the way you do when someone says to you, seconds after you’ve slammed your finger in a door, “At least it’s not broken”.