UNQUESTIONABLY, THE BIOLOGICAL theory of evolution by adaptive natural selection is one of the most significant ideas in human history. The fact that it remains contested by creationists to this day is proof enough of the impact it has had on humanity's perception of itself and the world, not least through its effects on religious thought, whose inclusive ambitions to explain the origins, duties and destiny of humankind it has impugned.

The outlines of evolutionary theory, and of the story of its discoverers, Charles Darwin and Alfred Russell Wallace, are familiar. Much less well known is the story of the complex debate which has surrounded the question of how the mechanism they proposed for evolutionary adaptation by natural selection actually works