What if humanity disappeared tomorrow?

According to Alan Weisman, author of "The World Without Us," in an interview with Scientific American, nature would reclaim the planet awfully quickly. In the event of an ecumenical rapture or a "12 Monkeys"-style plague, Manhattan's suppressed underground rivers would quickly reclaim the Big Apple's core, mosquitoes would thrive, feral cats would rule the roost, and the Statue of Liberty would wait for an enraged Charlton Heston who, like Godot, would never arrive.

Weisman isn't concerned with what might eradicate humanity; he's just interested in what the world would be like without us. People have long been fascinated by such ideas. There's even an environmental fringe group called the Voluntary Human Extinction Movement, dedicated to the dream of Earth returned to the pastoral bliss of the noble savage, hold the noble savages.

More typical, however, is the fixation on imagining the world emptied not of everybody but of everybody else. That was the plan of several James Bond villains, countless sci-fi writers and more than a few eugenicists who fantasized about starting from scratch with just a handful of humans.

The seductiveness of such daydreaming stems from a view of humans as a burden rather than a boon. It was the British economist Thomas Malthus more than anyone else who introduced the phobia that humanity reproduced itself at unsustainable rates. That thinking led to such apocalyptic egghead porn as Paul R. Ehrlich's 1968 treatise, "The Population Bomb," in which the biologist predicted that 65 million Americans would die amid global starvation in the 1980s. In case you missed it, that didn't happen.

The blind spot in the Malthusian vision is humanity's bottomless capacity for innovation. The "green revolution," for example, largely eliminated food scarcity.

In other words, our wealth is really all in our heads. Literally.

In the United States, for example, less than a fifth of our wealth exists as material stuff like minerals, crops and factories. In Switzerland, cuckoo clocks, ski chalets, cheese, Rolex watches, timber and every other tangible asset amount to a mere 16 percent of that country's wealth. The rest is captured by the expertise, culture, laws and traditions of the Swiss themselves.

These numbers come from Kirk Hamilton, a World Bank environmental economist and lead author of a new study, "Where is the Wealth of Nations?" (available at worldbank.org). In a fascinating interview in Reason magazine, Hamilton explains how, when measured properly, "natural capital" (croplands, oil, etc.) and "produced capital" (factories, iPods, roads, etc.) are the smallest slices of the economic pie. What Hamilton calls "intangible capital," which includes the rule of law, education and the like, is by far the biggest slice. The entire planet's "natural capital accounts for 5 percent of total wealth, produced capital 18 percent and intangible capital 77 percent.

This makes some intuitive sense. We'd all rather be the man who knows how to fish than the man given a fish. Or think of it this way: The Malthusian thinks only about hardware, when the money is in software and design. China makes America's iPods; America collects the profits.

Also, the richer a country gets, the less it needs to live off its natural resources. Therefore, it becomes cheaper - and more popular - to protect the environment. This has been the trend in Europe and America, and hopefully it will be around the world.

This sea change in economic thinking doesn't cut easily along the left-right political axis, and its implications could be profound. "Root-causes" liberals can find a great deal of satisfaction in the emphasis "Where is the Wealth of Nations?" places on education. According to Hamilton, education explains about 36 percent of a country's intangible wealth. Conservatives can find solace in the importance of property rights and, moreover, in the confirmation that not all cultures are equal - at least when measured on their ability to produce and sustain wealth. And both right and left will agree that the rule of law - including fair courts and government transparency - is the single most important contributor to a nation's wealth.

A potential lesson for the World Bank may be that building roads, dams and factories in the Third World is a fool's errand until those nations have the intangible capital required to maintain such things. The Marshall Plan's success in rebuilding Europe after World War II stemmed not from the U.S. footing the bill for concrete and bulldozers but from the intangible capital locked in the hearts and minds of everyday Europeans.

In an odd way, I think this complements Weisman's depiction of a post-human future. The greatest symbols of our civilization - from skyscrapers to libraries - not only count for a mere fraction of our wealth, they would turn to dust and rubble if we disappeared. The hardware is nothing; the software, everything. All that civilization is and can become exists within us. If we forget that, we forget literally everything.