Around the world, presidents and prime ministers mouth platitudes about sharing the pain of Haiti. But they should consider a simple question: how come only 63 people died when an earthquake of the same strength hit northern California 21 years ago?

The answer, of course, is that one is a rich country and the other decrepit. Poverty is the reason the sickly stench of death hangs over Haiti, not the terrible fury of nature.

Even before the quake, life was a desperate struggle. Three-quarters of the nine million people living in Haiti live on less than $2 a day. Half have no access to potable water. It has the highest rates of infant and maternal mortality in the West, and more people living with HIV/Aids than living with access to electricity.

The state is barely functioning. Corruption is so deep-rooted that nearly one-third of civil servants were found to be "phantom" employees. The president bemoaned the destruction of his tax offices this week, but it has been estimated 95 per cent of employment is in the underground economy. And how many people have jobs? No one really knows, although probably fewer than half the working age population.

This is why so many human beings had their lives destroyed in Port-au-Prince while their more fortunate brethren survived in San Francisco. Grinding poverty, compounded by festering corruption and shameful governance, led to the fallen buildings that killed thousands, the lack of a state response and the wrecked ports, collapsed hospitals and blocked roads.

Right now, Haiti desperately needs emergency aid. But longer term, the devastation should make us question the structural aid policies that have failed in Haiti just as they have failed in so many other countries.

Nine years ago William Easterly, a former World Bank economist, published a landmark book asking why more than one trillion dollars had been dispensed by the developed world in half a century to recipients who remained mostly poverty-stricken. Haiti was a key example of a nation that had frittered away huge sums.

The country continues to receive torrents of aid, with more than £3bn handed over since 1990. It is said to have more non-governmental agencies per head of population than anywhere else. Some indicators are improving, such as under-five death rates, although these also improved when much aid was suspended because of political upheaval. But the goal of genuine development remains as elusive as ever, demonstrated with shocking force once again this week.

Indeed, some aid has actually made Haiti's situation worse. The World Bank found a "total mismatch between levels of foreign aid and government capacity to absorb it", and donations have fanned corruption, cronyism and inequality. The United States, the biggest donor, insisted Haiti consumed American food transported on American ships, which hurt the local economy. Many of the best public servants left for the better pay offered by aid agencies.

These problems are not unique to Haiti and, of course, aid is not the cause of most of the country's problems. But similar problems have emerged elsewhere. And still no one has effectively answered the question posed by Easterly and, more recently, Zambian economist Dambisa Moyo.

Yet this week both Gordon Brown and David Cameron pledged to ensure Britain hits the target of handing over 0.7 per cent of national income in overseas aid.

This is a policy designed to appease domestic audiences. Long-term aid is important but should be based upon realistic assessment of needs and capabilities, not pressure from pop stars. The hallowed target, first calculated by lobbyists four decades ago, appears increasingly arbitrary. A study has found that applying the same methods of calculation to modern conditions would lead to a fraction of the amounts now being pledged.

When targeted, aid can be stunningly successful, as with the campaign to eliminate the scourge of guinea worm in Africa. But much of it is wasted, and it has often had unintended consequences that hinder rather than help development.

Haiti will need sustained assistance to recover. If we really want to help fragile nations, we should tear down trade barriers and crack down on banks that launder the plunder of corruption. We should liberalise drug laws that cause chaos around the world. And we should welcome more immigrants, since remittances sent back to families are the most direct and successful form of aid. But while helping the world's poor, such measures would create political storms at home.

i.birrell@independent.co.uk