“For some ancient Greeks and Romans, history was a downhill slide. … Nowadays some optimists think that history slants in the opposite direction. Some techno-utopians argue that technological progress is following an exponential curve, a J that is bending upward toward the vertical. … At the other extreme are today’s gloomy Malthusians. They view history as a spike, in which industrial and population growth overshoot the limits to sustainability, followed by a sharp crash likely to involve the collapse of industrial civilization … There is a third alternative: The shape of things to come may be a logistic curve or S-curve.”