Dolly—arguably the most famous sheep in world history—was born 20 years ago, on July 5, 1996. She was the first mammal ever to be cloned as an exact genetic copy of her mother, and born healthy. The scientific community and news headlines hailed the breakthrough and postulated that now human cloning would rapidly follow. Is that prospect something humankind should be sheepish about when we consider the potential dangers, or does it offer a solution to human mortality?