Zero population growth

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Zero population growth, sometimes abbreviated ZPG (also called the replacement level of fertility), [1] 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. [2] According to some, zero population growth, perhaps after stabilizing at some optimum population, is the ideal towards which countries and the whole world should aspire in the interests of accomplishing long-term environmental sustainability. [3] What it means by ‘the number of people neither grows nor declines’ is that births plus in-migrants equal deaths plus out-migrants. [4]



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. [5]

The American sociologist and demographer Kingsley Davis is credited with coining the term [6] [7] but it was used earlier by George J. Stolnitz, who stated that the concept of a stationary population dated back to 1693. [8] A mathematical description was given by James Mirrlees. [9]

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.” [10] Founding fathers of the movement were Paul Ehrlich, author of The Population Bomb , Richard Bowers, a Connecticut lawyer, and Professor Charles Lee Remington. [11] 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. fertility is at replacement level and birth and death rates are stable, a condition also called demographic equilibrium. Unstable rates can lead to drastic changes in population levels. This analysis is valid for the planet as a whole (assuming that interplanetary travel remains at zero or negligible levels), but not necessarily for a region or country 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 fertility rate (mean total number of children each woman has during her childbearing years) falls to the replacement level (the fertility rate which would result in equal birth and death rates for a population at equilibrium) and the point at which the population stops rising. [12] 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. Therefore, equilibrium, with a static population, will not be reached until the first "replacement level" birth cohorts reach old age and die. The related calculations are complex because the population's overall death rate can vary over time, and mortality also varies with age (being highest among the old).

Conversely, with fertility below replacement, a large elderly generation eventually results (as in an aging “baby boom”); but since that generation failed to replace itself during its fertile years, a subsequent “population bust”, or decrease in population, will occur when the 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 stabilize its 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.

However, even if there is zero population growth, there may be changes in demographics of great importance to economic factors, such as changes in age distribution.

How ZPG can be achieved

Number of demographic experts have suggested a few ways to reach zero population growth.

Biologist Alan D. Thornhill and Author Daniel Quinn argue that human population growth is a function of the human food supply [13] and that human population growth can only be achieved by an expanded food supply to support the growing population. In 1998, they produced a video entitled "Food Production and Human Population Growth" where they explain the theory and answer audience questions.

Albert Bartlett, an emeritus professor of physics at University of Colorado at Boulder in his lifetime, suggested that a population has the following choices to achieve ZPG:

  1. Voluntarily limit births and immigration to achieve zero population growth;
  2. Continue on the present path until the 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. [14]

Similarly, Jason Brent, another demographic expert, argues that there are three ways 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.
  3. By coercive population control prior to the human population exceeding the carrying capacity of the Earth. [15]

In China

China is the largest country by population in the world, having some 1.4 billion people. China is expected to have 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 [16] but, in November 2013, a relaxation of the one-child policy was announced amid unpopularity, reduced labour pool and support for an ageing population. [17]

In Europe

In Japan

See also

Related Research Articles

Demographics of China Aspect of human geography in China

The demographics of China demonstrate a large population with a relatively small youth component, partially a result of China's one-child policy. China's population reached 1 billion in 1982.

Demography The science that deals with populations and their structures, statistically and theoretically

Demography is the statistical study of populations, especially human beings.

Human population planning Practice of controlling rate of growth

Human reproduction planning is the practice of intentionally controlling the rate of growth of a human population. Historically, human population planning has been implemented with the goal of increasing the rate of human population growth. However, in the period from the 1950s to the 1980s, concerns about global population growth and its effects on poverty, environmental degradation and political stability led to efforts to reduce human population growth rates. More recently, some countries, such as China, Iran, and Spain, have begun efforts to increase their birth rates once again. While population planning can involve measures that improve people's lives by giving them greater control of their reproduction, a few programs, most notably the Chinese government's "one-child policy and two-child policy", have resorted to coercive measures.

In demography, demographic transition is a phenomenon and theory which refers to the historical shift from high birth rates and high infant death rates in societies with minimal technology, education and economic development, to low birth rates and low death rates in societies with advanced technology, education and economic development, as well as the stages between these two scenarios. Although this shift has occurred in many industrialized countries, the theory and model are frequently imprecise when applied to individual countries due to specific social, political and economic factors affecting particular populations.

Fertility is the natural capability to produce offspring. As a measure, fertility rate is the number of offspring born per mating pair, individual or population. Fertility differs from fecundity, which is defined as the potential for reproduction A lack of fertility is infertility while a lack of fecundity would be called sterility.

Birth rate

The crude birth rate in a period is the total number of live births per 1,000 population divided by the length of the period in years. The number of live births is normally taken from a universal registration system for births; population counts from a census, and estimation through specialized demographic techniques. The birth rate is used to calculate population growth. The estimated average population may be taken as the mid-year population.

Total fertility rate

The total fertility rate (TFR), sometimes also called the fertility rate, absolute/potential natality, period total fertility rate (PTFR), or total period fertility rate (TPFR) of a population is the average number of children that would be born to a woman over her lifetime if:

  1. She was to experience the exact current age-specific fertility rates (ASFRs) through her lifetime, and
  2. She was to survive from childbirth until the end of her reproductive life.
Sub-replacement fertility Total fertility rate that (if sustained) leads to each new generation being less populous

Sub-replacement fertility is a total fertility rate (TFR) that leads to each new generation being less populous than the older, previous one in a given area. The United Nations Population Division defines sub-replacement fertility as any rate below approximately 2.1 children born per woman of childbearing age, but the threshold can be as high as 3.4 in some developing countries because of higher mortality rates. Taken globally, the total fertility rate at replacement was 2.33 children per woman in 2003. This can be "translated" as 2 children per woman to replace the parents, plus a "third of a child" to make up for the higher probability of boys born and mortality prior to the end of a person's fertile life. In 2020, the average global fertility rate is around 2.4 children born per woman.

A population decline in humans is a reduction in a human population size caused by short term events such as pandemics, wars, famines or other catastrophes, or by long-term demographic trends, as in sub-replacement fertility rate, or persistent emigration.

Population ageing is an increasing median age in a population due to declining fertility rates and rising life expectancy. Most countries have rising life expectancy and an ageing population. This is the case for every country in the world except the 18 countries designated as "demographic outliers" by the UN. The aged population is currently at its highest level in human history. The UN predicts the rate of population ageing in the twenty-first century will exceed that of the previous century. The number of people aged 60 years and over has tripled since 1950, reaching 600 million in 2000 and surpassing 700 million in 2006. It is projected that the combined senior and geriatric population will reach 2.1 billion by 2050. Countries vary significantly in terms of the degree and pace of ageing, and the UN expects populations that began ageing later will have less time to adapt to its implications.

Population momentum is a consequence of the demographic transition. Population momentum explains why a population will continue to grow even if the fertility rate declines. Population momentum occurs because it is not only the number of children per woman that determine population growth, but also the number of women in reproductive age. Eventually, when the fertility rate reaches the replacement rate and the population size of women in the reproductive age bracket stabilizes, the population achieves equilibrium and population momentum comes to an end. Population momentum is defined as the ratio of the size of the population at that new equilibrium level to the size of the initial population. Population momentum usually occurs in populations that are growing.

Demographic trap

According to the Encyclopedia of International Development, the term demographic trap is used by demographers "to describe the combination of high fertility and declining mortality in developing countries, resulting in a period of high population growth rate (PGR)." High fertility combined with declining mortality happens when a developing country moves through the demographic transition of becoming developed.

Kingsley Davis was an internationally recognized American sociologist and demographer. He was identified by the American Philosophical Society as one of the most outstanding social scientists of the twentieth century, and was a Hoover Institution senior research fellow.

Ansley Johnson Coale, was one of America's foremost demographers. A native to Baltimore, Maryland, he earned his Bachelor of Arts in 1939, his Master of Arts in 1941, and his Ph.D. in 1947, all at Princeton University. A long-term director of the Office of Population Research at Princeton, Coale was especially influential for his work on the demographic transition and leadership of the European Fertility Project.

Rate of natural increase crude birth rate minus the crude death rate

In demography, the rate of natural increase (RNI) is a statistic calculated by subtracting the crude death rate from the crude birth rate of a given region.

Ageing of Europe

The aging of Europe, also known as the greying of Europe, is a demographic phenomenon in Europe characterised by a decrease in fertility, a decrease in mortality rate, and a higher life expectancy among European populations. Low birth rates and higher life expectancy contribute to the transformation of Europe's population pyramid shape. The most significant change is the transition towards a much older population structure, resulting in a decrease in the proportion of the working age while the number of the retired population increases. The total number of the older population is projected to increase greatly within the coming decades, with rising proportions of the post-war baby-boom generations reaching retirement. This will cause a high burden on the working age population as they provide for the increasing number of the older population.

Population may refer to:

Family planning in India Bharat

Family planning in India is based on efforts largely sponsored by the Indian government. From 1965–2009, contraceptive usage has more than tripled and the fertility rate has more than halved, but the national fertility rate in absolute numbers remains high, causing concern for long-term population growth. India adds up to 1,000,000 people to its population every 20 days. Extensive family planning has become a priority in an effort to curb the projected population of two billion by the end of the twenty-first century.

Population planning in Singapore

Population planning in Singapore spans two distinct phases: first to slow and reverse the boom in births that started after World War II; and second, from the 1980s onwards, to encourage parents to have more children because birth numbers had fallen below replacement levels.

Generation Alpha Generation born between the early 2010s and the mid 2020s.

Generation Alpha is the demographic cohort succeeding Generation Z. Researchers and popular media use the early 2010s as the starting birth years and the mid-2020s as the ending birth years. Named after the first letter in the Greek alphabet, Generation Alpha is the first to be born entirely in the 21st century. Most members of Generation Alpha are the children of Millennials.


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