[2][3] However, it was used earlier by George J. Stolnitz, who stated that the concept of a stationary population dated back to 1693.
[5] In the late 1960s, ZPG became a prominent political movement in the U.S. and parts of Europe, with strong links to environmentalism and feminism.
Yale University was a stronghold of the ZPG activists who believed "that a constantly increasing population is responsible for many of our problems: pollution, violence, loss of values and of individual privacy.
"[6] Prominent advocates of the movement were Paul Ehrlich, author of The Population Bomb, Richard Bowers, a Connecticut lawyer, and Professor Charles Lee Remington.
[9] The reason for this is that even though the fertility rate has dropped to replacement level, people already continue to live for some time within a population.
Achieving ZPG in the short run is difficult because a country's population growth is often determined by economic factors, incidence of poverty, natural disasters, disease, etc.
A loosely defined goal of ZPG is to match the replacement fertility rate, which is the average number of children per woman which would hold the population constant.
[15] In November 2013, a relaxation of the one-child policy was announced amid unpopularity and the forecast of a reduced labor pool and support for an aging population.