For panarchy? It's a complex theory about how complex we've made the world, after several long cycles of change and adaptation --and why human civilization may now be on the cusp of social and ecological collapse. Here's the money quote, from ecologist Buzz Holling--which he said before the worldwide economic meltdown:

This is a moment of great volatility and instability in the world system. We need urgently to do what we can to avoid deep collapse. We also need to figure out how to exploit the opportunity provided by crisis and collapse when they occur, because some kind of systemic breakdown is now almost certain.

The theory of panarchy is the subject of Thomas-Homer Dixon's new book, The Upside of Down: Catastrophe, Creativity, and the Renewal of Civilization. The current issue of WorldWatch is excerpting a chapter, which contains an interesting discussion with Holling, who believes the world is reaching "a stage of vulnerability that could trigger a rare and major 'pulse' of social transformation." Dixon argues that

Humankind has experienced only three or four such pulses during its entire evolution, including the transition from hunter-gatherer communities to agricultural settlement, the industrial revolution, and the recent global communications revolution. Today another pulse is about to begin.