This short story from the collection Wild Child was originally published in the New Yorker.
Dámaso Funes is a medical miracle. He didn't make a sound when he was born, and as the years go by it's found that he doesn't feel pain. Not when he picks up hot coals with his bare hands or when he breaks his leg. To his father he is a sideshow freak, a spectacle from which he can make money, but to the village doctor who delivered him he is much more. He is a marvel, a wonder of genetics - the next step of human evolution.