‘There are’, some great sage once said, ‘two kinds of people: those who think there are two kinds of people and those who don’t.’ For Peter Watson, the ‘Great Divide’ separates the Americas from the rest of the world. ‘Until roughly 1500,’ he says, ‘there were two entirely separate populations on earth, one in the New World, one in the Old’, with ‘markedly different trajectories of civilisation’. (Here and in all subsequent quotations from the book, the italics are the author’s, who scatters them with a hand as free as a Victorian matron’s.) Watson characterises the divergent paths that he detects as leading to ‘more vivid religion’ and ‘more organized violence’ in the New World than elsewhere. When compared they reveal, he assures us, ‘a unique opportunity to see how nature and human nature interact, to explain ourselves to ourselves’.

His project is one ‘not carried out before’. The reader who contemplates the following 600-odd pages may be tempted to feel grateful for previous authors’ restraint. On the face of it, the enterprise looks pointless. Obviously there were never only ‘two entirely separate populations on earth’. Isolation has afflicted many