behavior is always changing, all the time. Our planet is a dynamic, active environment. Weather is changing. The land is changing. Continents drift. … - Michael Crichton

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behavior is always changing, all the time. Our planet is a dynamic, active environment. Weather is changing. The land is changing. Continents drift. Oceans rise and fall. Mountains thrust up and erode away. All the organisms on the planet are constantly adapting to those changes. The best organisms are the ones that can adapt most rapidly. That’s why it’s hard to see how a catastrophe that produces a large change could cause extinction, since so much change is occurring all the time, anyway.” “In that case,” Thorne said, “what causes extinction?” “Certainly not rapid change alone,” Malcolm said. “The facts tell us that clearly.” “What facts?” “After every major environmental change, a wave of extinctions has usually followed — but not right away. Extinctions only occur thousands, or millions of years later. Take the last glaciation in North America. The glaciers descended, the climate changed severely, but animals didn’t die. Only after the glaciers receded, when you’d think things would go back to normal, did lots of species become extinct. That’s when giraffes and tigers and mammoths vanished on this continent. And that’s the usual pattern. It’s almost as if species are weakened by the major change, but die off later. It’s a well-recognized phenomenon.