Before the Second World War, the Ministry of War confidently predicted what would happen when London was bombed from the air by Nazi planes. There would be, they warned, "a mass outbreak of hysterical neurosis among the civilian population." For every one person injured, there would be dozens who lose their morals or lose the plot. They would howl and they would loot and they would rape. Humans couldn't take it. They would break. They would turn on each other.

The same predictions are made about every disaster -- that once the lid of a tightly policed civilization is knocked off for a second, humans will become beasts. But the opposite is the case. It will sound grotesque to say that we should see reasons for hope as we watch in realtime while the earth is shaken six inches on its axis, tsunamis roar, and nuclear power stations teeter on melt down. But it is true. From this disaster, we can learn something fundamental about our species. It should guide how the Japanese authorities behave today -- and fatally puncture right-wing ideologies based on the belief humans are inherently selfish tomorrow.

The evidence gathered over centuries of disasters, natural and man-made, is overwhelming. The vast majority of people, when a disaster hits, behave in the aftermath as altruists. They organize spontaneously to save their fellow human beings, to share what they have, and to show kindness. They reveal themselves to be better people than they ever expected. When the social scientist Enrico Quarantelli tried to write a thesis how people descend into chaos and panic after disasters, he concluded: "My God! I can't find any instances of it." On the contrary, he wrote, in disasters "the social order does not break down... Co-operative rather than selfish behavior predominates." The Blitz Spirit wasn't unique to London: it is universal.

On April 18th 1906, San Francisco was leveled by an earthquake. Much of the city collapsed, and the rest began to burn. Anna Amelia Holshouser -- a middle-aged journalist -- was thrown out of bed, and then felt her house collapse all around her. She wandered the streets, and found herself sleeping that night in the park. But then the daze wore off, and she did what almost everybody else did: she began to look after the people around her. She knitted tents out of old clothes to house all the children who had lost their parents. She set up a soup kitchen, and the local shop-keepers handed over the goods for free. Hundreds of people gathered there, as they were gathering around similar people across the city. Anna put up a sign that said: "One Touch of Nature Makes the Whole World Kin."

In San Francisco that week, all the city's plumbers began -- unpaid -- to fix the broken pipes, one by one. People organized into committees to put out the fires with buckets and anything they could find. The philosopher William James, who watched, wrote: "Everybody was at work... and the discipline and order were practically perfect." It had been an incredibly divided city, prone to race riots against Chinese immigrants. But not after the disaster struck. San Fransicans handed out food and clothes to astonished Chinese people. A young girl called Dorothy Day watched her mother give away all her clothes to survivors, and wrote: "While the crisis lasted, people loved each other."

They hated what had happened, but they loved what they had become. There are going to be a thousand stories like this from Japan. In her gorgeous book A Paradise Built In Hell: The Extraordinary Communities That Arise In Disaster, Rebecca Solnit shows how this is how almost everybody responds to disaster, across continents and across contexts. When power grids are destroyed and city grids demolished, social grids light up.

This is so cross-cultural -- from Haiti to New Zealand -- that it is probably part of an evolved instinct inherent to our species, and it's not hard to see why. We now know that 60,000 years ago, the entire human race was reduced to a single tribe of 2000 human beings wandering the savannahs of Africa. That was it. That was us. If they -- our ancestors -- didn't have a strong impulse to look out for each other in a crisis, you wouldn't be reading this now.

Yet there are a few examples stubbornly fixed in the popular imagination of people reacting to a natural disaster by becoming primal and vicious. Remember the gangs "marauding" through New Orleans, raping and even cannibalizing people in the Super-Dome after Hurricane Katrina? It turns out they didn't exist. Years of journalistic investigations showed them to be racist fantasies. They didn't happen. Yes, there was some "looting" -- which consisted of starving people breaking into closed and abandoned shops for food. Of course human beings can behave atrociously - but the aftermath of a disaster seems to be the time when it is least likely.

This information is essential for knowing how to respond to disasters. There is a fear that the Japanese government is with-holding information about the dangers of the nuclear meltdown because they don't trust the people to react sensibly and calmly. There is no way of knowing, yet, whether this is true. But understanding this crucial history should guide the government to tell the truth and trust the people. As Solnit puts it: "If you imagine that the public is a danger, you endanger the public." They are the allies of public safety, not its enemy. After the Three Mile Island meltdown in Pennsylvania in 1979, nearly 150,000 people were evacuated. The government was not in charge. Ordinary people spontaneously coordinated it themselves, without panic.

Even inside the World Trade Center on 9/11, people were remarkably orderly and altruistic. The disabled people who worked in the Towers were not abandoned by panicking colleagues. They were all carried out by their workmates -- including people from floors above where the planes hit.

In a disaster, very few people are on-yer-bike individualists grabbing for themselves, and they are regarded as incomprehensible by everybody else. After the 2005 tsunami, the Ayn Rand Institute -- set up by the philosopher-queen of the American right -- issued an appeal entitled: "U.S. Should Not Give To help Tsunami Victims." (This was entirely consistent with her world-view: she said it was immoral to save a drowning person if there was any risk to yourself.) Even the people who every day take this callous view of victims within our own societies -- the poor, the homeless, the ill -- felt the need to distance themselves from this sociopathy.

It's often implied that kindness and generosity are naïve, idealistic fictions that will always be trumped by self-interest and greed. This is at the core of a particular kind of right-wing ideology that has been ascendant for thirty years now. But when the stakes are highest, the opposite is the case. When everything else is stripped away, when the buildings fall and the seas rise, we remember all that really matters is caring for each other.

This raises an obvious question. Can we hold onto this impulse after the disaster passes? Can we spread it? Dorothy Day never forgot how her mother behaved that week in San Francisco - and it inspired her to set up a radical movement to house and empower the poor that continues to this day. Will we remember to hold on to our sense of inspiration?

This is likely to be a century of escalating ecological disasters, since each year we destabilize our climate more, in the face of plain scientific warnings. It's hard to extract any hope from the picture this fact presents us with. But there is some. Alongside this impulse to denial and self-destruction, there is something fundamentally good in us. We are humans. We care about each other. We will -- at the most crucial and final moment -- sacrifice for each other, like the technicians who are trying to prevent the nuclear plant melting down, knowing this is probably personal suicide. That's something to hold onto. Normally, in Northern Japan, the night sky is blocked out by the yellow-orange haze of light pollution. Tonight, huddled together, the people there can see the stars.

Johann Hari is a writer for the Independent. To read more of his articles, click here or here. You can email him at j.hari [at] independent.co.uk