Conventional wisdom tells us that grain price rallies during the past few years have been caused by concerns over a rising population and rising wealth in the developing world. As people become richer, they eat more meat, and livestock needs significant amounts of grain to fatten up. Indeed, worldwide meat production has tripled over the past four decades and increased 20pc in the past 10 years, according to research from the Worldwatch Institute, the environment organisation. The pressure group noted that industrial countries are consuming growing amounts of meat, nearly double the quantity in developing countries. If this trend continues,...