According to demographers, the population of the world reached one billion in 1804. Earth arrived at the second billion by 1927. Three billion in 1959. Four billion in 1974. In May of this year, our planet was estimated to be inhabited by 7.6 billion people. According to the UN’s revised projections (2017), we may reach 8.6 billion in 2030, 9.8 billion by 2050, and ll.2 billion by 2100.

Some commentators, such as The Wall Street Journal’ s William McGurn (Main Street, May 1, 2018), continue to make sport of Paul Ehrlich’s 1968 book, The Population Bomb. But how many know that the author’s original title was Population, Resources, and the Environment? The book is a sensible call to examine how population growth could impact the Earth’s future in light of our known resources, and how all of this could in turn condition where we live (the environment). These considerations are brought up to date in essays by Chris Clugston and Leon Kolankiewicz in this issue of The Social Contract.

The United States and other economically developed countries in Europe, Australia-New Zealand, and parts of Asia, such as Japan, South Korea, and Singapore, have all undergone what is described as the “Demographic Transition” from high birth and death rates, to having fewer children as they have gotten richer. But as Frosty Wooldridge outlines in his survey published in this issue, the “Demographic Transition” is not taking place in Africa, India, and China. Far from it. These areas are overpopulated by at least a factor of three. And we are seeing some of the consequences. Overpopulation is highly destabilizing. It makes war more likely and can trigger unexpected environmental surprises. Right now, for example, Nigeria (Africa’s most populated country, estimated to reach 400 million by 2050 from 186 million) is being wracked by a war between Christian farmers and Muslim herdsmen. “The clashes could foreshadow broader resource wars across West Africa’s Sahel—the semi-arid region bedeviled by a confluence of rising jihadist activity and surging migration—and around the continent,” report Joe Parkinson and Gbenga Akingbule (“Deadly Farmland Fight Shakes Nigeria,” Wall Street Journal, May 29, 2018, p. A9).

What to do? As Garrett Hardin reminded us, “We fail to mandate economic sanity because our brains are addled by compassion.” He argued that we need to accept the limits of the Earth’s resources and make the hard choices necessary to live within them (see Hardin, this issue, p. 29; also his Living Within Limits: Ecology, Economics, and Population Taboos, Oxford University Press, 1993).