Fewer, Richer, Greener

3The Demographic Transition: Running Out of and Into People¹

How do population explosions begin? How do they end? Why do people start having fewer children when they start to get ahead economically? Population dynamics involves a number of mysteries, some of which we’ll explore in this chapter.

In Chapter 2, we heard from the British demographer Thomas Malthus, who lived about two centuries ago. The environmentalist Ted Nordhaus describes Malthus’s view as follows: “In response to abundance, humans would respond with more—more children and more consumption. Like protozoa or fruit flies, we keep breeding and keep consuming until the resources that allow continuing growth are exhausted.”² Looking backward at history, Malthus was not wrong to arrive at this conclusion.

But we are not protozoa or fruit flies. We are intelligent beings that respond to incentives; we can shape our environment. Nordhaus explains,

In reality, human fertility and consumption work nothing like this. Affluence and modernisation bring falling, not rising fertility rates. As our material circumstances improve, we have fewer children, not more. The explosion of human population over the past 200 years has not been a result of rising fertility rates but rather falling mortality rates.³

As families either consciously or instinctively respond to the lower death rates by lowering the birth rate, the population stabilizes at a new, higher level—and will do so, according to the best forecasts, at a level less ...