Almost every bone and muscle in our body has a counterpart in chimps. We’re nothing new, evolution just tweaked things a bit. One area with the most modifications is our hips. Chimps have tall, narrow hips; good for propping up an arched body. However, ours are short and wide. They’re great for our vertical body to “sit in” and be supported.
Of course, that’s not the only adaptation our pelvis has for walking upright. Muscle attachment sites have changed to give them increased power during bipedalism. Joints and bones have become thicker to deal with the fact our torso’s entire weight passes through the pelvis.
But that’s not all. Anatomists have discovered a previously unknown way our hip helps us walk. It’s been speculated about since the ’90s but has only just been confirmed. The secret advantage? Our hips are very wide. It’s perverse.
Big steps for big success
We use a lot of little tricks to help us walk upright. Most of them you probably aren’t consciously aware of, but they’re still vital if you want to be bipedal.
For example, as we push off with our rear foot we turn our toes into a lever. This gives the leg a bit of extra oomph as we take the step. We twist our hips as we step, bringing the foot closer to the ground and so reducing the damage on impact. And our arms swing back and forth to help counterbalance this rotation and stop up tripping over. The list goes on.
But one of the biggest advantages you can have when it comes to walking upright is long legs. The list of benefits to these is long. More legs mean more space for your muscles to act on, increasing their potential power. Plus many parts of the leg work as a lever, like the aforementioned toes. And a longer lever is a better lever.
As such, it should come as no surprise that our legs have been getting longer and longer over the course of human evolution. Early on we had arms longer than our legs. Now, your legs add up to 1/3 of your body weight. It’s a dramatic change crucial to give us the efficient walking we used to leave Africa.
Evolution has given us long, efficient legs. But our legs also use a few tricks to become even longer. The way you use your tip toes whilst walking, for example, artificially increases their length at key moments in your gait. Well, as artificial as something your body naturally does can be.
For years some researchers have speculated that our wide hips might also give us a bit of a length boost. As your pelvis as you walk, that extra width becomes leg length. At least, that’s the theory.
Of course, it’s all well and good drawing some diagrams and making inferences. But does the hip actually contribute to stride length? There have been a few attempts to test this over the years, but by far the most rigorous one came out recently. Researchers carefully measured a subject’s hips, before getting them to walk. Sure enough, those with wide hips took longer strides.
And who has the widest hips? Typically women. The aforementioned research was part of a special edition journal on the pelvis I read. Because I’m exciting like that. And it included another article doing research on this subject. Except they noted that women should have shorter strides because they’re generally smaller. However, they could use their wide hips to compensate for this. By rotating their pelvis a bit more to better use their extra width they could easily compensate for their generally shorter legs.
So the hips did lie, but it was for our benefit.
Gruss, L.T., Gruss, R. and Schmitt, D., 2017. Pelvic breadth and locomotor kinematics in human evolution. The Anatomical Record, 300(4), pp.739-751.
Whitcome, K.K., Miller, E.E. and Burns, J.L., 2017. Pelvic rotation effect on human stride length: Releasing the constraint of obstetric selection. The Anatomical Record, 300(4), pp.752-763.