But the Broadbalk field shows something else. Chart 1 tracks its yields from the start, showing how the three different kinds of wheat farming—African, Green Revolution and modern—have diverged, sometimes quite suddenly: in the 1960s with the introduction of new herbicides for Green Revolution wheat, and in the 1980s with new fungicides and semi-dwarf varieties. Worryingly, though, in the past 15 years the yields of the most productive varieties of wheat in Broadbalk have begun to level out or even fall. The fear is that Broadbalk may prove a microcosm in this respect, too.

At the start of 2011 the food industry is in crisis. World food prices have risen above the peak they reached in early 2008 (see chart 2). That was a time when hundreds of millions of people fell into poverty, food riots were shaking governments in dozens of developing countries, exporters were banning grain sales abroad and “land grabs” carried out by rich grain-importing nations in poor agricultural ones were raising awkward questions about how best to help the poor.

This time, too, there have been export bans, food riots, panic buying and emergency price controls, just as in 2007-08. Fears that drought might ruin the current wheat crop in China, the world’s largest, are sending shock waves through world markets. Discontent over rising bread prices has played a part in the popular uprisings throughout the Middle East. There are differences between the periods, but the fact that agriculture has experienced two big price spikes in under four years suggests that something serious is rattling the world’s food chain.

The food industry has been attracting extra attention of other kinds. For years some of the most popular television programmes in English-speaking countries have been cooking shows. That may point to a healthy interest in food, but then again it may not. The historian Livy thought the Roman empire started to decay when cooks acquired celebrity status.