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Ears of plenty
IN 10,000 years, the earth's population has doubled ten times, from less than 10m to more than six billion now and ten million soon. Most of the calories that made that increase possible have come from three plants: maize, rice and wheat. The oldest, most widespread and until recently biggest of the three crops is wheat (see chart). To a first approximation wheat is the staple food of mankind, and its history is that of humanity.

Yet today, wheat is losing its crown. The tonnage (though not the acreage) of maize harvested in the world began consistently to exceed that of wheat for the first time in 1998; rice followed suit in 1999. Genetic modification, which has transformed maize, rice and soyabeans, has largely passed wheat by—to such an extent that it is in danger of becoming an “orphan crop”. The Atkins diet and a fashion for gluten allergies have made wheat seem less wholesome. And with population growth rates falling sharply while yields continue to rise, even the acreage devoted to wheat may now begin to decline for the first time since the stone age.

It is time to pay tribute to this strange little grass that has done so much for the human race. Strange is the word, for wheat is a genetic monster. A typical wheat variety is hexaploid—it has six copies of each gene, where most creatures have two. Its 21 chromosomes contain a massive 16 billion base pairs of DNA, 40 times as much as rice, six times as much as maize and five times as much as people. It is derived from three wild ancestral species in two separate mergers. The first took place in the Levant 10,000 years ago, the second near the Caspian Sea 2,000 years later. The result was a plant with extra-large seeds incapable of dispersal in the wild, dependent entirely on people to sow them.

The story actually starts much earlier, around 12,000 years ago. ...