Rosemary and Peter Grant and those assisting them have spent 20 years on Daphne Major, an island in the Galapagos, studying natural selection. They recognize each individual bird on the island, when there are 400 at the time of the author's visit or when there are over a thousand. They have observed about 20 generations of finches - continuously. Jonathan Weiner follows these scientists as they watch Darwin's finches and come up with a new understanding of life itself.