Zero population growth, sometimes abbreviated ZPG (also called the replacement level of fertility), is a condition of demographic balance where the number of people in a specified population neither grows nor declines, considered as a social aim. According to some, zero population growth is the ideal towards which countries and the whole world should aspire in the interests of accomplishing long-term environmental sustainability.
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. This replacement fertility will depend on mortality rates and the sex ratio at birth, and varies from around 2.1 in developed countries to over 3.0 in some developing countries.
The American sociologist and demographer Kingsley Davis is credited with coining the term but it was used earlier by George Stolnitz, who stated that the concept of a stationary population dated back to 1693. A mathematical description was given by James Mirrlees.
In the late 1960s ZPG became a big 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.” Founding fathers of the movement were Paul Ehrlich, author of The Population Bomb, and Thomas Eisner. Ehrlich stated: “The mother of the year should be a sterlized woman with two adopted children.”
In the long term, zero population growth can be achieved when the birth rate of a population equals the death rate, i.e. replacement level is met and rate is stable. Unstable rates can lead to drastic changes in population levels. (This ignores migration, which is valid for the planet as whole, but not necessarily for a nation.) A population that has been growing in the past will have a higher proportion of young people. As it is younger people who have children, there is large time lag between the point at which the birth rate falls below the death rate and the point at which the population stops rising.
Conversely, a large elderly generation can be the result of an aging “baby boom”, but if that generation had failed to replace its population during its fertile years, the result is a subsequent “population bust”, or decrease in population, as that older generation dies off. This effect has been termed birth dearth. In addition, if a country's fertility is at replacement level, and has been that way for (at least) several decades (to adjust for changes in age distribution), then that country's population could still experience coincident growth due to continuously increasing life expectancy, even though the population growth is likely to be smaller than it would be from natural population increase.
Zero population growth is often a goal of demographic planners and environmentalists who believe that reducing population growth is essential for the health of the ecosystem. Preserving cultural traditions and ethnic diversity is a factor for not allowing human populations levels or rates to fall too low. Achieving ZPG is difficult because a country's population growth is often determined by economic factors, incidence of poverty, natural disasters, disease, etc.
In China 
China is the largest country by population in the world (though India has about the same population, and has a higher birth rate), being home to 1.3 billion people. China is expected to witness a zero population growth rate by 2030. China's population growth has slowed since the beginning of this century. This was mostly the result of China's economic growth and increasing living standards which led to the decline. However, many demographers also credit China's family planning policy, which was formulated in the early 1980s, encourages late marriages and late childbearing, and limits most urban couples to one child and most rural couples to two children. Without the policy, the country's population would be 400 million more than the current 1.3 billion people. According to the government projection, the work-age population will then drop to 870 million. The Chinese government is hoping to see the zero population growth in the future.
In Europe 
In Japan 
See also 
- Birth credit
- Demographic transition—Zero population growth is achieved when the birth rate of a population equals in a situation where net migration is also zero
- Overpopulation—when an organism's numbers exceed the carrying capacity of its habitat.
- Population Matters (formerly known as the Optimum Population Trust)—A registered United Kingdom charity, think tank and campaign group
- Steady state economy
- Z.P.G.—A science-fiction movie concerning the topic of zero population growth.
- Zero growth
- Zero Population Growth Organizanion. "Zero Population Growth." BookRags Staff. N.p., 2005. Web. 7 Oct. 2009. <http://www.bookrags.com/research/zero-population-growth-enve-02/>
- Kingsley Davis (1973) "Zero population growth: the goal and the means" in The No-Growth Society, Mancur Olson & Hans H. Landsberg, eds. New York: Norton
- Last, John M. "Zero Population Growth." Healthline. N.p., 2002. Web. 5 Oct. 2009. <http://www.healthline.com/galecontent/zero-population-growth>.
- Davis, Kingsley (1967). "Population policy: Will current programs succeed?". Science 158 (3802): 730–739. doi:10.1126/science.158.3802.730. PMID 6069101.
- Kingsley Davis Obituary
- Stolnitz, George J. (1955). "A Century of International Mortality Trends_ I". Population Studies (Population Investigation Committee) 9 (1): 24–55. doi:10.2307/2172340. JSTOR 2172340.
- Mirrlees, J. A. (1967). "Optimum Growth When Technology is Changing". The Review of Economic Studies (The Review of Economic Studies Ltd.) 34 (1): 95–124. doi:10.2307/2296573. JSTOR 2296573.
- “ZPG – A New Movement Challenges the U.S. to Stop Growing”, LIFE magazine, April 27, 1970, page 12ff
- Xiang, Zhang (21 July 2009). "China expected to see zero population growth by 2030: expert". China View. Retrieved 2010-03-01.
- Population Connection
- Enviro, Population Movements Merge Goals for Healthier Planet
- World Watch Institute
- Northwest Environment Watch
- Center for Environment and Population—Science, Policy, and Public Education on Population and the Environment]
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