Paddies can be self-fertilising too because decaying plants and animal waste break down in the water, producing nitrogen which nourishes the crop. The paddy system is so productive that, throughout human history, the world’s densest populations have been rice-growing cultures.40 The surplus food generated allowed people to conceive of a future, plan ahead and divide labour, so that some people were free to craft objects, create art, own possessions or gain prestige. As farmers domesticated rice, they shaped civilisation.
