The earliest known prosthesis, dating possibly as far back as 950 B.C., was discovered in Cairo on the mummified body of an ancient Egyptian noblewoman. The prosthesis is made largely of wood, molded and stained, its components bound together with leather thread. It is, as prostheses go, tiny.
Because it is a toe.
The prosthetic digit—the oldest little piggy in the world—is extraordinarily lifelike, its curved nail sunken into a similarly curved bed. Which is, in its way, remarkable. A toe! One that is several thousand years old! And it's not just a toe-sized peg—a little device that would have made mobility more manageable for someone who was, by reasons of birth or amputation, missing her big toe. The prosthesis is, as much as it possibly could be, humanoid: maximally lifelike and maximally toe-like. The "Cairo Toe," as it's been dubbed, is prosthetic and cosmetic at once—evidence not just of ancient manufacturing stepping in where biology was limited, but of manufacturing engaging in an ancient form of biomimcry.
Compare the Cairo Toe to today's prostheses, many of which—especially those that dominate the public imagination—seem to be inspired less by "man," and more by the Bionic Man. The blades. The hooks. The exoskeletons. This week alone has brought news of a roboticized prosthetic hand that, possibly inspired by the workings of the claw crane, foregoes five fingers for three. It has brought news of a woman who created her own prosthetic leg ... out of LEGOs. Those stories come as part of a flood of coverage of the next generation of prostheses, in which technologies from adjacent fields—3D-printing, robotics, chemistry—are helping humans to transcend nature's narrow definition of humanity.
These devices—and this is the most important thing—will make life better for the many people who need them. But it's also worth noting that their impulse—the body, made more powerful or more beautiful through technological augmentation—is in some ways extremely un-prosthetic. These newest devices are less about technology filling in where nature has been limited and more about technology bettering nature itself. They're less about replication, and more about amelioration.