How the Potato Changed the World: From Andean Tuber to Half of Europe's Dinner

Wild potatoes grow from the American southwest to Chile, and the cultivated potato was domesticated around Lake Titicaca on the border of Peru and Bolivia between 8,000 and 10,000 years ago, from a wild species that had to be bred out of its bitterness. The Andean farmers made it the basis of a civilisation at altitudes where maize will not grow, cultivating thousands of varieties in every colour and shape, matched to particular fields and frosts, and they invented freeze-drying: chuno, potatoes left out to freeze at night, trodden to squeeze the water out, and dried in the day, keeps for years and fed the Inca armies and storehouses. The Spanish, who arrived in 1532, took the tuber to Europe in the 1570s as a curiosity, and it was grown for a century in botanic gardens and by a few farmers before anyone else would eat it.

The potato had everything against it. It was a member of the nightshade family, and its green parts and its sprouts are indeed poisonous; it grew from lumps rather than seed, which struck people as unnatural; it was ugly and it was unmentioned in scripture; and it was associated with the Irish and the poor. Governments pushed it because they could see what it would do. Frederick the Great of Prussia ordered his peasants to plant it in 1756 and, in a story that may be legend, posted guards around a royal potato field to make it seem worth stealing; Antoine-Augustin Parmentier, who had eaten little else as a prisoner in Prussia, persuaded Louis XVI to wear potato flowers and served potato dinners to Paris society, and French dishes with his name still carry the tuber. By 1800 it was a field crop across northern Europe, and the reasons were arithmetic:

• •A hectare of potatoes yields two to four times the food energy of a hectare of wheat
• •It grows in poor, wet, cold soil where grain fails, and on plots too small for a plough
• •It supplies nearly everything a person needs: energy, protein, vitamin C, potassium and B vitamins; a diet of potatoes and milk is nutritionally complete
• •It cannot be taxed or requisitioned easily, since it stays in the ground until dug, and armies marching over a field of it could not burn the crop

The historian William McNeill argued that the potato, more than any machine, made industrial Europe possible: it fed the growing population that filled the factories, released land from grain, and let a family live on a garden plot while its members worked for wages. The population of Europe roughly doubled between 1750 and 1850, and studies attribute a substantial part of the growth, and a measurable part of the urbanisation, to the tuber. Ireland was the extreme case. By 1840 about a third of the Irish population lived almost entirely on potatoes, an adult man eating five kilograms a day, and the population had risen to over eight million on land that grain could not have fed.

In 1845 a water mould, Phytophthora infestans, arrived from the Americas and destroyed the crop in a week, turning the tubers to black slime in the ground, and it returned in 1846 and 1848. Ireland had one main variety, the Lumper, cloned from cuttings and genetically identical, and no resistance anywhere. About a million people died of hunger and disease and a million and a half emigrated, and the island's population has never returned to its 1841 level; the British government's response, which continued grain exports and insisted on relief through workhouses and public works, is the reason the famine remains a political wound. Blight is still the potato's chief enemy, controlled by spraying and by breeding, and the same mould caused the potato crisis in the Netherlands and Germany in the 1840s that helped set off the revolutions of 1848.

The potato is the world's fourth food crop after maize, wheat and rice, at around 375 million tonnes a year, and China grows the most. It is a mainstay of the diet from Peru to Poland, it has been to space, and a genebank in Lima holds some 4,500 Andean varieties against the day another blight arrives. The chip, invented in Belgium or France in the eighteenth century, and the crisp, invented in America in the nineteenth, have turned it into the most processed vegetable on Earth, and a plant that was once accused of causing leprosy is now more often accused of causing obesity, which is a measure of how completely it won.

The potato was domesticated near Lake Titicaca some 8,000 years ago, reached Europe with the Spanish in the 1570s, and was distrusted for two centuries as poisonous, unnatural and unbiblical until kings and reformers pushed it as a crop that yielded several times the food of grain on poor land. It fed the doubling population of industrial Europe and above all Ireland, where dependence on a single clone met the blight of 1845 and a million died, and it is now the world's fourth food crop.