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Furthermore, this pattern of increase was set back by five massive extinction episodes. The most recent of these, during the cretaceous period, is by far the most famous, because it ended the age of the dinosaurs, giving authority to the mammals, thus ultimately making possible the dominance of the human species over the earth. But the cretaceous crisis was minor compared with the Permian extinction 240 million years ago.

IF YOU meet a bear in the woods, try not to panic or scream; on no account should you turn your back and run. As markets around the world have turned grizzly over the past two weeks, some investors seem to have forgotten the old hikers' maxim. Until recently, financial markets appeared to be betting that the Goldilocks economy—neither too hot, nor too cold—was safe from the bears. The rattled markets are a reminder that sooner or later growth will slow or inflation will rise. Inflation is not about to spiral upwards but with diminishing spare capacity, it could edge up. America has an extra risk because Wall Street suspects that Ben Bernanke, the Fed's new chairman, may be a soft touch on inflation. If that suspicion persists, he will need to raise interest rates by more than otherwise—or investors will do the tightening for him by pushing up bond yields. That would make other assets look expensive. It is in the American housing market that the bear may growl loudest. By borrowing against the surging prices of their homes, American consumers have been able to keep on spending. The housing market is already coming off the boil

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