There are no ends, limits, or walls that can bar us or ban us from the infinite multitude of things.

—Giordano Bruno, On the Infinite Universe and Worlds, 1584

When a population of organisms grows in a finite environment, sooner or later it will encounter a resource limit. This phenomenon, described by ecologists as reaching the “carrying capacity” of the environment, applies to bacteria on a culture dish, to fruit flies in a jar of agar, and to buffalo on a prairie. It must also apply to man on this finite planet.

—John P. Holdren and Paul R. Ehrlich, Global Ecology, 1971