By Ding Xuedong To the people, food is the most important issue under the sky.” So says an old Chinese proverb; but if that is so, the clouds may be darkening. As the world’s population grows – and as its people grow more prosperous and more carnivorous – it will only become more difficult to provide a plentiful supply of food at affordable prices. I n many countries, food security is already an urgent challenge, as the world food price crisis of 2007-08 showed. According to research by the UN Food…