Zero population growth
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 by some. 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. What it means by ‘the number of people neither grows nor declines’ is that births plus in-migrants equal deaths plus out-migrants.
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 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.” 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 sterilized 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 is valid for the planet as whole, but not necessarily for a nation as it ignores migration. 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.
How ZPG can be achieved
Number of demographic experts have suggested a few ways to reach zero population growth.
Albert Bartlett, an emeritus professor of physics at University of Colorado at Boulder in his lifetime, suggested that the population have following choices to be at ZPG:
1. Voluntarily limit births and immigration to achieve zero population growth;
2. Continue on the present path until our population is so large that draconian measures become necessary to stop the growth of population;
3. Do nothing and let nature stop the growth through disease, starvation, war and pestilence. If humans do not solve the problem, nature will.
Similarly, Jason Brent, another demographic expert, argues that there are three to achieve zero population growth. His argument is as follows:
1. By war, with or without weapons of mass destruction, starvation, disease, rape, murder, ethnic cleansing, concentration camps, and other horrors beyond the imagination, when humanity has exceeded the carrying capacity of the Earth.
2. By the voluntary action of all of humanity prior to the human population exceeding the carrying capacity of the Earth. If any group or even if a single-family failed to control its population the entire program would fail. For example, Mr. Justice Scalia had nine children and if each of those had nine and if in each generation each offspring had nine, then in just 11 generations about 31 billion Scalias would live on the planet. That is the power of compound growth.
3. By coercive population control prior to the human population exceeding the carrying capacity of the Earth.
China is the largest country by population in the world, being home to some 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 1970s, encourages late marriages, late childbearing, and the use of contraceptives, and since 1980 has limited most urban couples to one child and most rural couples to two children. According to government projections, the work-age population will then drop to 870 million. It was said, in 2009, that the Chinese government was hoping to see zero population growth in the future but, in November 2013, a relaxation of the one-child policy was announced amid unpopularity, reduced labour pool and support for an ageing population.
- 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
- List of population concern organizations
- Overpopulation—when an organism's numbers exceed the carrying capacity of its habitat.
- Pledge two or fewer (UK family limitation campaign)
- Steady state economy
- Z.P.G.—A science-fiction movie concerning the topic of zero population growth.
- Zero growth
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