Much publicity greeted a recent study, funded by Motorola, that showed that young people in Japan—heavy users of portable electronics—have developed unusual thumbing powers. They're even starting to ring doorbells with their thumbs and point with their thumbs. There are reports of people typing 40 words a minute with thumbs alone.

Does this mean that thumbs are evolving before our eyes? Might thumbs, for example, migrate farther up the side of the hand? Become more pointy? Pivot better?

Behavior precedes anatomy—that seems to be a general rule in evolution. So in theory, a behavioral change could lead to a different kind of thumb. But learned traits aren't passed on to future generations.

For the thumb to evolve as a result of cell phone use, people whose genetic codes give them unusually nimble thumbs would need to pass along more of their genes than folks with clumsy, plodding, brutish thumbs. For example, great thumbwork might be considered alluring to potential mates, though the opposite seems more likely. ("Excuse me, darling, I need to make a quick call.") Or maybe only those with lightning-quick mutant thumbs would be able to call 911 before all the lines got tied up. But again, it seems more likely they'll remove themselves from the gene pool by making cell phone calls while driving.

Research on thumb evolution looks not to the future but to the past—or at least to our closest living relatives. Although most other primates have opposable thumbs, their thumbs are shorter, farther down on the hand, and their fingers are longer and less straight. To pick up a grain of rice, a chimp may need to squeeze it between its thumb and the side of its index finger, the way a person might hold a key. The human thumb is fingerlike—it's a precision grasper.

Randy Susman, an anatomist at Stony Brook University, has identified muscles attached to our thumb that other primates lack. For example, there's the flexor pollicis longus. It runs the length of the forearm and helps control the thumb when you mash something. (Mash a thumbtack into a wall and you'll feel it tense up.)

The human hand, Susman says, got its current form around two million years ago. But tools came first, he notes—anatomy followed. The very first tools may never be found. "They were no doubt nondurable—sticks, grass stems for termite fishing, and broken nuts for cutting and slicing."

The cell phones back then, needless to say, were horribly bulky.

—Joel Achenbach
   Washington Post Staff Writer