Over the past 160 years our numbers have doubled and doubled and almost doubled again. Never before have we seen such a huge rise in human population in so few generations. Never again will we. Today our population growth is slowing down. In 
Over the past 160 years our numbers have doubled and doubled and almost doubled again. Never before have we seen such a huge rise in human population in so few generations. Never again will we. Today our population growth is slowing down. In 1859 Charles Darwin wrote of “the numerous recorded cases of the astonishingly rapid increase of various animals in a state of nature, when circumstances have been favorable to them during two or three following seasons.” Using examples ranging from minuscule seedlings to giant elephants, he discussed the very rare cases in nature when exponential population growth occurred in a species. In fact, the best example he could have picked would have been that of his own species, humans, who at that time were just beginning their own unprecedented, exponential, worldwide increase in numbers.
Today slowdown (a word first used in the 1890s, meaning to go forward more slowly) affects far more than our rate of population growth. It affects almost every aspect of our lives. Our current slowdown represents a huge challenge to the expectation of acceleration, and a step into the unknown. To what extent are our current belief systems (economic, political, and otherwise) built on assumptions of rapid future technological change and perpetual economic growth? Accepting that a slowdown is upon us will require us to shift our fundamental view of change, innovation, and discovery as unalloyed benefits. Will we be able to accept that we should stop expecting ceaseless technological revolutions? The possibility that we might not sensibly be able to do so is itself frightening. What mistakes will we make if we assume that slowdown is unlikely and new great shifts lie just around the corner? What will happen if things stay much the same as they are now while the rate of change simply slows down?
Imagine that you have spent your life on a speeding train and you suddenly feel the brakes being applied. You would worry what was about to happen next. Now imagine that not just you but all the people you know— as well as their parents, grandparents, and great-grandparents, as far back as anyone can remember—have all lived on that very same speeding train, and that the train has been accelerating for virtually all of their lives. For you, hurtling forward at breakneck speed is comfortingly normal, but now you can begin to feel the slowdown, a new and frightening feeling. However, because the train is still rushing forward, people all around you are