The State exists to feed people. Politicians proclaim defence or law and order or social issues or wealth creation or health as their priority. But without food, nothing else matters. For most of history, leaders were those who knew how to get it - sometimes by hunting prowess, sometimes by means of a gift for commanding herds, sometimes by naked power, forcing subjects to work in the fields and dig ditches, and sometimes by mediating with the gods or spirits of nature.

Food gave rulers their legitimacy. Rulers lasted only as long as they kept people fed. Today's leaders - many of whom have gathered in Rome today for a world food security summit - have failed in this most elementary of obligations.

When food gives out, revolutions follow. Famine helped to precipitate the Ming dynasty to power in China. French revolutionaries asked Marie Antoinette for bread before they called for her head. One reason why the British gave up their Indian Raj was an awareness that they could not cope with famine. Food failure can bring down whole civilisations.

The Natufians of Syria - the first sedentary civilisation in the world, whose people once enjoyed such abundance that they could build permanent settlements while living on wild grains and products of the hunt - ran out of food 14,000 years ago. The graves of Minoan Crete, where oil and grain once filled the great palace labyrinths, are full of malnourished bones. Environmental overkill helped to exhaust the soil and empty the cities of the Maya lowlands towards the end of the first millennium, when jungle choked the hundreds of temples that once towered above the treetops.

A couple of centuries later, food failure wiped out the civilisations in the south west of North America. The Aztec empire collapsed when invaders cut off its supplies. Famines checked growth repeatedly in Europe until new crop varieties solved perennial food shortages in the 18th century.

Today's failure to deliver food for the people is worldwide. In the West, it means higher grocery bills. In much of the rest of the world, it means hunger. In at least 30 countries, it means famine. The price of staple grains has risen by an average of 80 per cent over the past two years. Some prices have trebled.

The psychological trauma is acute because the world has gone from comparative abundance to life-destroying dearth in less than a generation. Between the 1960s and 1980s, the “green revolution” - the development of high-yield hybrid staples - stacked up stockpiles and saved millions of lives. At the same time, aid agencies, governments and the United Nations revolutionised distribution and emergency response time. Now that achievement has crumbled. We seem unable to produce enough food, or to get what we can spare to those who need it.

The political convulsions have begun. The world's hunger victims are biting rubber bullets. In Haiti, the starvelings have rebelled. In West Africa, Egypt, Bangladesh, Indonesia and Madagascar they are rioting. In the West, governments' votes fall as grocery bills rise. The pundits' prescription - genetically modified food - will make the problems worse, by increasing wealth gaps, condemning poor farmers to dependency and multiplying environmental risks.

Meanwhile, most economists expect, at best, only a modest easing of prices, So is the world headed the way of the Natufians, Maya and Minoans?

A few comforting facts are worth bearing in mind. Supply will adjust to demand, especially in India and China, where most of the recent new demand has arisen. There are plenty of underexploited food resources in the world, especially in the sea, which constitutes 90 per cent of the biosphere, and is still seriously underexploited. Fish farming seems an unromantic substitute for old-fashioned fishing, but it increases the yield of selected species thousands of times over.

Although it would be disastrous if widely applied to foodstuffs, GM could solve the biofuel problem and save acreage by providing fuel from high-yielding plants. If all else fails, technology could turn plankton, insects and edible bacteria into something palatable. There is enormous scope for rationalising food distribution, and redeploying the food that the rich world wastes. Demand will slacken in any case as world population stabilises - which is bound to happen, although it may happen too late to save us.

It is normal for the world to be short of food. The brief era of cheap eating has been a disaster for the world. People in the rich world have eaten too much food, fattening themselves into obesity and sickness in consequence. Most of us would be better off with tighter belts. To make food cheap, we have poisoned farmland with chemicals, squandered precious water, abused marginal terrain and undermined biodiversity.

Low prices have impoverished farmers in the developing world. The poorest are locked into poverty - compelled, in effect, to produce surpluses of cheap grains and forgo the traditional and rare crops that might command a decent price in a fussier, pricier world market: the green revolution suppressed such exotic crops as quinoa, tef and

criollo potatoes - which the Western bourgeoisie is avidly rediscovering, now that they are rare and costly.

Mass demand for cheap standard varieties helped to strip traditional foods - including Britain's best apples and strawberries - from greengrocers' shelves. Huge tracts of productive land were smothered for housing, industry and the curse of “leisure” - really just a crass euphemism for mindless forms of expensive idleness. Ironically, cheap food has been a main cause of the present shortages, because it has made food production economically unattractive.

So it is time to put our money where our mouths are. If we valued food more, we would have more of it at higher standards. We would eat more sparingly and more discriminatingly. We would have more of those delicious rare varieties, because we would be willing to pay for them. The present shortages may provoke bloody revolutions as well as harrowing famines. But if they cause a revolution in our attitudes, their longer-term effects will transform the world for the better. We have to get used to paying more for food - and to learn to like it.

Felipe Fernández-Armesto is a historian. His books include Food: A History and Civilizations

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