The pilgrims’ progress

A hundred million years ago, our ancestors were nocturnal mouse-like creatures, living in the shadows of the dinosaurs. Five hundred million years ago, our ancestors were fish, living near (or even in) the sea bottom. Two thousand million years ago, they were single-celled microbes, floating in the sea. Almost 4,000 million years ago, they were replicating molecules, lacking almost every feature that we expect in something that is live — except reproduction.

The evolutionary history of life is one of science’s great stories — a story that educated people like to know at least in outline, along with the history of European civilisation and the political history of their own country. There is a steady supply of new popular science books that describe it and, at one level, Richard Dawkins’ The Ancestor’s Tale is the latest offering of this kind.

But Dawkins tells the story differently from almost everyone else. He tells it backwards. The book’s title alludes to Chaucer, and Dawkins imagines a band of pilgrims who travel back in time. We (that is, human beings) send back one band of pilgrims. Other life forms, such as chimpanzees, hippopotamuses, and axolotls, also send back pilgrims. From time to time — in the order of our evolutionary kinship — two pilgrim bands unite and continue on back in time together. Thus, human pilgrims meet chimpanzee pilgrims at a point corresponding to 5 million years ago; the combined bands of all placental mammals meet kangaroos at a point corresponding to 140 million years ago, and then fish pilgrims 400-plus million years ago.

The book’s design allows Dawkins to write a series of essays, united by the reverse chronology. As each pilgrim band joins, they tell a tale about their way of life.