Darwin convinced us that all life on Earth is related by common
descent. It was a stunning overturning of the convention wisdom
of simultaneous creation. The task then was to discern the
familial relationships of all species of life on Earth,
including the many extinct organisms known through the fossil
record. Biologists did this on the basis of morphological
similarities. A zebra is presumably more closely related to a
horse than to a elephant, and so on. By the middle of the last
century a family tree of life on Earth had been established to
almost everyone's satisfaction. Then came the most astonishing
surprise. In every cell of our bodies we carry a history of our
species' past, written in the four-letter genomic code. Forget
looking at the morphology of zebras, horses and elephants. Send
their DNA unlabeled to the sequencing lab and the genes will
tell which creatures are more closely related, and (with a bit
of calibrating against the fossil record) how long ago any two
species shared a common ancestor