For most of history these man-made enclaves remained very small, surrounded by expanses of untamed nature. The earth’s surface measures about 200 million square miles, of which 60 million is land. As late as AD 1400, the vast majority of farmers, along with their plants and animals, clustered together in an area of just 4.25 million square miles – 2 per cent of the planet’s surface.2 Everywhere else was too cold, too hot, too dry, too wet, or otherwise unsuited for cultivation. This minuscule 2 per cent of the earth’s surface constituted the stage on which history unfolded.
