“The hand, for instance, is not simply a system of levers that makes it possible to grasp and manipulate objects, nor is it merely a sensory organ; it is in fact the instrument which makes possible many of our greatest technological and artistic achievements. It allows us to explore our world, to fashion instruments, to touch a loved one, and to create works of art. It is, to put it simply, an extension of the brain, without which the brain as we know it could not have evolved. The muscles that support upright posture, our shoulders, limbs, and voice—all are tangible aspects of our higher selves. To understand our physical design is to understand the underpinnings of our intellectual, social, and artistic lives.”