People, like most animals, are naturally lazy. So the ascent of mankind is something of a mystery. Humans who make their livings hunting and gathering in the traditional way do not have to put much effort into it. Farmers who rely on rain to water their crops work significantly harder, and lead shorter and unhealthier lives. But the real back-breaking, health-destroying labour is that carried out by farmers who use irrigation. Yet it was the invention of irrigation, at first sight so detrimental to its practitioners, that actually produced a sufficient surplus to feed the priests, politicians, scholars, artists and so on whose activities are collectively thought of as "civilisation". Given all the extra effort involved, why people first bothered to plant crops, and more particularly why they then went on to plant them near rivers running through deserts-with all the attendant canal-digging that required-is a puzzling question. But some light was shed on it at a recent meeting of the American Geophysical Union, in San Francisco. It may all, it seems, be down to climate change.
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