The basic problem is thusly summed up :

During the second half of the 20th century, the world's population multiplied by 2.4, i.e. it increased from 2.5 billion persons in 1950 to 6 billion in 2000. During the same time, agricultural and food production multiplied by 2.6 (FAO, Faostat). Thus, the latter progressed a little more quickly than the population. Furthermore, the global agricultural output growth has been much higher during the last 50 years than during the 10,000 years of agricultural history. While bypassing the most optimistic expectations, this gigantic progress has limits and drawbacks however : three quarters of the peasants in the world are still working with manual tools only (e.g. hoe, spade, digger stick, machette, harvester knife, sickle...). Meanwhile, one third of humanity suffers from serious food deficiencies, and farmers constitute the majority of the poor and of the undernourished of the planet.

The majority of peasants in the third world are stuck with agricultural methods that went out of fashion in the High Middle Ages... And the productivity that comes with it : whereas these tools only allow a worker to cultivate about 1 hectare,  or 2.5 acres by himself, and yield thus 1 ton of grain from his work, a 1900 European or American peasant, using animal traction and basic industrially produced tools, could cultivate ten times the area, and get about 10 tons of grain for his work, and thus was already 10 times more productive ; the modern peasant of the developed world, with industrial machinery, can cultivate 200 hectares, and the increased yield of modern crops means his production may reach 2,000 tons of grain - that worker is thus two thousand times more productive...

This extraordinary rise in productivity - and production - is faster than population growth : thus grain prices, over the 20th century, have been steadily going down. Because of that, even the extremely productive peasants of the developed countries have to be heavily subsidized. But the Third World farmer, facing not only his dismal productivity, also often does not own as much land as he could cultivate : because of overpopulation, as in Bangladesh, and because of inequality in land distribution, as in Latin America, where latifundism means a few landowners own most of the land, leaving the rest with too little land to live on.

These small peasants, who are in the majority in Africa - 80% of land workers - and in South America - 60% - could rise their productivity if they could have access to the selected varieties of the Green Revolution, buy some animals, increase the size of their holdings. But because food prices are low, selling enough grain to make those improvements would leave them starving - a bad year already means starving, because some of the grains have to be sold anyway, to pay debts or taxes.

Many of these rural peasants have to leave the countryside and move to the slums, attracted to large city life, and the higher income that can be gained there. But this surplus of labour means wages remain very low in the city - and when food prices rise, these new urbanites can't eat any more.

Thus governments are faced with contradicting incentives : urban populations demand for cheaper food, whereas rural development requires higher prices, less the country's agriculture disappears. Developed countries, on the other hand, lobby for the ability to export their surplus grain in the third world, which fits well with the "Free Trade For Everything" mood in international relationships. Of course, this means many countries see their food independence greatly diminished. And actual famine comes in underdeveloped peasants, who in a bad yield can't buy enough food before the next harvest.

The choice of low food price and free trade, or protectionism and higher food prices, is thus an arbitrage between the demands of the angry urban population and the needs of the hungry rural farmers. But is a solution that implies letting agriculture in developing countries rot a real solution ?

Another consequence of the rural exodus is that the less productive land in the third world is given up and remains fallow. But as the population keeps rising, as the unsustainability of some of the more intensive agricultural methods lower the most impressive yields, these lands will be needed one day too. If there is nobody left knowing how to cultivate them, there is going to be a problem...