“The possibility must be considered seriously that the number of people on the Earth has reached, or will reach within half a century, the maximum number the Earth can support in modes of life that we. . . will choose to want.” —-Joel Cohen, How Many PeopleCan the Earth Support"

“The ultimate resource is people—skilled, spirited, and hopeful people who will exert their wills and imaginations for their own benefit, and so, inevitably, for the benefit of us all.” —-Julian Simon, The Ultimate Resource

Entering into the population debate is like stepping into a conversation that has been going on for centuries. Since ancient times people have argued over what the size of their communities should be. The formal scientific study of human populations—demography—can be traced back to an eighteenth-century English clergyman, Thomas Malthus. In his 1798 treatise, An...