In the closing years of this millennium, a quiet, unassuming British embryologist named Ian Wilmut set out to improve the productivity of farm animals and along the way set off a biological earthquake. The experiment he tenaciously pursued--to get a cell from an adult mammal to behave like a cell from a developing embryo--had long since been abandoned at the major centers of scientific research. Even high school biology students knew that once a mammalian cell had differentiated, and was programmed by nature to be bone or nerve or skin, it could not be deprogrammed.
Yet Wilmut did it. From...