Ecological competition began as slow arms races. Predators evolved to hunt. Prey evolved to defend themselves. Each improvement was small, barely shifting the odds of survival. Nature remained in equilibrium. Until the dawn of humanity. When our ancestors developed the unique ability to think up new devices and behaviors, humanity became able to overcome nature's defenses far more quickly than natural selection could respond. Humankind spread out of Africa, wiping out most of the megafauna in its path-mammoths, sabertooth cats, elephant-sized sloths, and a great many other species. Today, this formidable, inventive genius of our species-now grown to overwhelming and all-conquering proportions-is threatening to make the earth unlivable, even for ourselves. The only weapon available to us to counter this threat is, ironically, the same one that unleashed our destructiveness in the first place: the analytical and creative power of the human brain.