IT IS CONCEIVABLE, THEN, THAT A LIVING ORGANISM—whether the product of evolution or genetic engineering—could threaten our great transformation into a city-planet. But there is reason for hope. We have a window of a few decades where DNA-based microbes will retain the capability of unleashing a cascading epidemic that kills a significant portion of humanity. But at a certain point—perhaps ten years from now, perhaps fifty—the window may well close, and the threat may subside, just as other, more specific, biological threats have subsided in the past: polio, smallpox, chicken pox.
