Sometimes, when I watch someone recovering from a brain injury it seems as though I am watching the evolution of the brain in fast-forward mode. I’m thinking about evolution today because I just read a fascinating article that asserts that mankind’s predecessors learned to walk in the tree limbs, rather than by ambling along on flexed knees, dragging the knuckles of their hands on the ground for balance.
As a student of physical therapy, I was taught that primitive reflexes underlie many of our more sophisticated motor patterns and that these primitive reflexes are often revealed by brain damage. A strong extensor thrust forms the basis of our ability to bear weight on our legs. A flexor withdrawal underpins our ability to pick up a leg and swing it, in preparation for the next step. Therapists find these deeply wired-in patterns revealed in almost every spastic stroke or cerebral palsy or traumatic brain-injured patient they treat. But there’s one other thing that I always see—almost invariably, my patients turn their legs outward and hold them close together when they first start walking. It’s a big reason why they’re so unstable on their feet: they have a small base of support and they trip over their own feet. What purpose would that almost universal pattern of movement have served in creatures that had advanced from quadruped to bipedal gait on open terrain? None at all! I often tell my patients that they look like they are trying to walk on a tight rope. Perhaps, evolutionally speaking, they are! Compare the image of a young orangutan inching out on a tree limb, holding to another branch for support with what we see when human children learn to stand erect and take their first steps by holding onto furniture and “cruising along” sideways.
It’s exactly what I ask my patients to do—hold onto a rail or a window sill or the kitchen counter and step sideways. I do it because it gives patients a sense of control and lets them build balance skills in a safe and effective manner. Who knew that we might be following in the footsteps of our arboreal ancestors? And perhaps that familiar tight-fisted grip and stubbornly flexed arm seen on many neurological patients are also reminders of a tree-swinging past.