"So most of earth's history shows animals living and dying against a very active background. That probably explains 90 percent of extinctions. If the seas dry up, or become more salty, then of course ocean plankton will all die. But complex animals like dinosaurs are another matter, because complex animals have insulated themselves - literally and figuratively - against such changes. Why do complex animals die out? Why don't they adjust? Physically, they seem to have the capacity to survive. There appears to be no reason why they should die. And yet they do.

"What I wish to propose is that complex animals become extinct not because of a change in their physical adaptation to their environment, but because of their behavior. I would suggest that the latest thinking ill chaos theory, or nonlinear dynamics, provides tantalizing hints to how this happens.

It suggests to us that behavior of complex animals can change very rapidly, and not always for the better. It suggests that behavior can cease to be responsive to the environment, and lead to decline and death. It suggests that animals may stop adapting. Is this what happened to the dinosaurs? Is this the true cause of their disappearance? We may never know. But it is no accident that human beings are so interested in dinosaur extinction. The decline of the dinosaurs allowed mammals - including us - to flourish. And that leads us to wonder whether the disappearance of the dinosaurs is going to be repeated, sooner or later, by us as well. Whether at the deepest level the fault lies not in blind fate-in some fiery meteor from the skies - but in our own behavior. At the moment, we have no answer."