What a waste are two thumbs on the space bar. There they sit, nearly flaccid, punctuating the end of each word, awaiting the call to crack stone or to use sharp flakes to incise wood.
It is easy to think of other traits as making us human. We talk, use metaphors, empathize, follow fashions, laugh, play politics and Angry Birds. But many of us still work with our hands, crafting fine objects or simple tools, digging and harvesting. Or texting. As they have always done, thumbs and fingers connect us to our social lives.
No living ape has such digits, each long thumb with its own wide, flat fingertip bone. Ape thumbs are short afterthoughts, jutting awkwardly below the long, strong bones of the hand. No ape supplies each thumb with its own flexor pollicis longus, deep in the forearm. This muscle pulls powerfully on the thumb bones, clamping them forcefully onto the stone. The pinky bones, too, get into the act, flexing inward to cup the palm around a rock. No ape has a pinky as mobile as ours, or short fingers with broad fingertips. Those wide fingertips, wider than any ape or monkey’s, spread the pressure over a broader surface, making the grip fast against the percussive rebound as the stone wallops into another at the abrupt end of its arm-driven ballistic path.