It’s a popular myth, or at least an oversimplification, that opposable thumbs are uniquely human and separate us from other animals. That’s simply not true. Virtually all primates have opposable thumbs…chimps, gorillas, orangutans, baboons and bonobos. Many also have opposable big toes, which humans have largely lost through evolution. Bonobos are particularly interesting in this context because they’re one of our two closest living relatives (along with chimpanzees), sharing roughly 98.7% of our DNA. Their hand anatomy is quite similar to ours. Some non-primate animals have convergently evolved similar gripping ability. Koalas, giant pandas (sort of), even some opossums have that ability.
But what really makes humans different in this regard is a few things in combination. Human thumb proportions are important since human thumbs are longer relative to finger length than any other primates, enabling finer precision grip. Muscle configuration, the opponens pollicis, is also more developed in humans, allowing greater rotation. Brain-hand coordination, the neurological sophistication connecting intent to fine motor execution is uniquely developed in humans. And, of course, humans are freed from locomotion. Chimps and bonobos use their hands for knuckle-walking, which compromises fine grip. Human hands are entirely liberated for manipulation.
The neurological fine motor control connecting brain to hand is more developed in humans. What’s interesting about bonobos specifically is that they have shown in captivity that they can learn surprisingly sophisticated manual tasks, using tools in research settings. This suggests the limiting factor isn’t really the thumb anatomy so much as the brain-hand coordination and, crucially, the social learning infrastructure that allows humans to accumulate and transmit tool knowledge across generations. That last point… cumulative cultural transmission… is arguably what separates human tool use from everything else in the animal kingdom. The thumb is the hardware. So why does the myth about opposable thumbs persists? It’s a useful shorthand. “Opposable thumbs” became cultural shorthand for the suite of manual dexterity advantages humans have, even if the term itself is imprecise. It’s the combination of thumb anatomy, brain wiring, fully bipedal posture freeing the hands, and social transmission of tool skills that’s truly unique. So the thumb is important, but it’s really a system, not a single feature that sets humans apart. Humans have what’s called “full opposability” where the thumb can rotate and flex to meet the pad of every other finger with precision. This comes from a unique saddle joint at the base of the thumb (the carpometacarpal joint) combined with a muscle called the opponens pollicis that no other primate has in quite the same configuration. The median nerve controls this muscle, which is why carpal tunnel syndrome can cause that characteristic weakness at the base of the thumb. Some evolutionary anthropologists argue the opposable thumb is the single physical trait most responsible for human civilization. Everything from writing to surgery to playing an instrument flows from it. It’s one of those anatomical features you don’t appreciate until something threatens it, which is why its all on my mind right now.
It’s been four days now since I had my trip to the ER to see if I had suffered a stroke or TIA. The real reason had everything to do with my sudden left thumb weakness and I have been left with no answers from any quarter. I am learning each day all the things you can’t do when your opposable thumb (even just one of them) doesn’t work right. It started with my inability to button my right cuff button, even after five minutes of trying. My left thumb just wouldn’t push the button through the buttonhole. Then, there were my compression socks that have become an every-day part of my new, more active life, lived without edema. While compression socks suffer from a reputation of being too hard to put on, I was doing fine with two healthy thumbs, but its a lot harder to pull up your socks with a hinky left thumb. The left one goes on fine, but that thumb just won’t pull the right one the way it needs to. Gripping a water glass, opening a tube of Chapstick, holding a beard trimmer…turns out they all need a left thumb. Then today, the primary insult. I pulled up to the drive-in ATM to get some cash and found that my left hand without a fully functioning thumb, was not having an easy time of taking my cash out of the dispenser…damn! It turns out that despite all the physiological anthropology, opposable thumbs are a necessary part of my civilized life. Strangely enough, since typing on QWERTY keyboards allows you to use either thumb for the space bar, it doesn’t seem to be impeding my keyboarding…yet.
I have now gone out into the garden for three days and dug holes, planted all sorts of plants, moved new and heavy pots and hefted many bags of bark mulch to spread them around my newly cleared and planted sections of garden. None of those things require much fine motor skills, so my thumb works well enough to let me do what is needed. But open a garden knife to slit a bag of mulch open and I’m back in kindergarten trying to use scissors awkwardly. It’s hard to tell if its getting marginally better each day, but its clearly more than a simple sore muscle at play. I need to try some new tactics.
My friend Steven asked his “care team” of doctor golfing buddies, what I should do. They said that “these things can pop up at any time, especially as one ages” and that it should improve all by itself. OK, but that seems a bit passive. Our friend Phillip had two more proactive suggestions. He told me to try acupuncture. Possibly, though the evidence is mixed and depends heavily on what’s actually causing the weakness. Where acupuncture has reasonable evidence is for nerve compression conditions like carpal tunnel syndrome (CTS). There’s actually a decent body of research suggesting acupuncture can help with pain and sensory symptoms — numbness, tingling, that kind of thing. Some studies show it compares favorably to steroid injections for mild to moderate CTS in the short term. But for actual motor weakness — the kind where the opponens pollicis muscle at the base of your thumb is atrophying or losing function — acupuncture is on much shakier ground. That type of weakness typically means the median nerve is under enough compression that the motor signal is being significantly disrupted. That’s a structural problem that usually needs a structural solution. Thumb weakness specifically — at the thenar muscles — is a fairly classic sign of median nerve compromise, whether from carpal tunnel, a more proximal compression, or something systemic.
Then Phillip mentioned Gyrotonics. Gyrotonics is a movement system developed by a former ballet dancer that combines elements of yoga, swimming, gymnastics, and tai chi. It uses a specialized pulley and resistance system to guide the body through circular, spiraling movements rather than linear ones. The emphasis is on decompressing joints, lengthening while strengthening, and coordinating breath with movement. It turns out that the flowing, rotational movements can mobilize the wrist, forearm, and shoulder in ways that reduce compression along the entire nerve pathway. It addresses the cervical spine and shoulder girdle, which is relevant if nerve issues originate higher up in the neck rather than just at the wrist. The decompression emphasis is directly relevant to nerve entrapment because it’s creating space rather than loading joints. It tends to improve postural alignment, which reduces chronic nerve compression from slouching and forward head position, something I clearly can use. It turns out there is a Gyrotonics practitioner here in Escondido.
So, I am not giving in to the wait-and-see approach, nor to the view that my human “software” can make up for whatever “hardware” deficiency has suddenly afflicted my left thumb. I am going to see the Gyrotonics lady tomorrow and work on my thenar muslces (especially the opponens pollicis), the median nerve, my C6, C7 or C8 spinal nerve roots or whatever else ails me. I just hope I can hold onto my money to pay her with my left hand…..