When human beings were all still hunter-gatherers, each needed about a thousand hectares of land to support him or her. Now – thanks to farming, genetics, oil, machinery and trade – each needs little more than a thousand square metres, a tenth of a hectare. (Whether the oil will last long enough is a different subject and one I tackle later in the book: briefly my answer is that substitutes will be adopted if the price rises high enough.) That is possible only because each square metre is encouraged to grow whatever it is good at growing and global trade distributes the result to ensure that
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