It is a zone of conflict and upheaval, where the old and the new are constantly at War. Finding the balance point must be a delicate matter - if a living system drifts too close, it risks falling over into incoherence and dissolution; but if the system moves too far away from the edge, it becomes rigid, frozen, totalitarian. Both conditions lead to extinction. Too much change is as destructive as too little. Only at the edge of chaos can complex systems flourish."

He paused. "And, by implication, extinction is the inevitable result of one or the other strategy -too much change, or too little."

In the audience, heads were nodding. This was familiar thinking to most of the researchers present. Indeed, the concept of the edge of chaos was very nearly dogma at the Santa Fe Institute.

"Unfortunately," Malcolm continued, "the gap between this theoretical construct and the fact of extinction is vast. We have no way to know if our thinking is correct. The fossil record can tell us that an animal became extinct at a certain time, but not why. Computer simtulations are of limited value. Nor can we perform experiments on living organisms. Thus, we are obliged to admit that extinction - untestable, unsuited for experiment - may not be a scientific subject at all. And this may explain why the subject has been embroiled in the most intense religious and political controversy. I would remind you that there is no religious debate about Avogadro's number, or Planck's constant, or the functions of the pancreas. But about extinction, there has been perpetual controversy for two hundred years. And I wonder how it is to be solved if -Yes? What is it?"

At the back of the room, a hand had gone up, waving impatiently. Malcolm frowned, visibly annoyed. The tradition at the Institute was that questions were held until the presentation ended; it was poor form to interrupt a speaker. "You had a question?" Malcolm asked.