The rice that came from nowhere

Between 1960 and 2000 world cereal production roughly tripled while the area farmed grew by about ten per cent. Most of the additional food came from the same land, and the change was deliberate.

The central idea is easy to state and was not obvious at the time. Traditional wheat and rice plants were tall. Given plenty of fertiliser they grew taller still, became top-heavy and fell over before harvest, which meant that adding nutrients past a certain point reduced the yield rather than raising it. Breeders therefore selected for short, thick-stemmed varieties. A short plant puts less of its energy into stem and more into grain, and it stays standing under a heavy head.

The results were extraordinary and they were not free. The new varieties depend on reliable irrigation and on fertiliser, which favoured farmers who could afford both and in several regions widened the gap between them and those who could not. Planting large areas with a small number of genetically similar varieties made crops more vulnerable to a single disease. Heavy fertiliser use changed the chemistry of rivers downstream.

Historians still argue about the balance, and the argument is not really about the facts, which are largely agreed. It is about which consequences you count and over what period.

What is not in dispute is the scale. Estimates of the number of famine deaths avoided run into the hundreds of millions, which is a difficult number to hold alongside the costs and a dishonest one to leave out.