Malthus’s Essay on Population, published in 1798, still plays a role in environmental policymaking. The discrepancy between rates of human population growth and agricultural productivity lies at the heart of Malthusianism. One dynamic leads to ever-increasing population; the other to diminishing food and ecological degradation.
In the decade just after World War 2, the ideas of Thomas Robert Malthus made a comeback. Becoming acutely aware of rapid population increase and degradation of environments, we learned to speak of a “population explosion.” A rumor circulated that there might be more humans alive in our time than the sum of all past populations. Although the rumor was mathematically incorrect, it expressed a valid concern.
If descendants of the 950 million contemporaries of Malthus in 1798 had continued doubling every 25 years (as he reported the people in England’s colonies in America had been doing), there would be today 242 billion people on this planet. That would be more than the total of all past human births.
To avoid human suffering, Malthusians pursue worldwide zero population growth (ZPG). Because worldwide mortality levels are low, a society can attain ZPG through replacement fertility. If the average number of children born to women in a particular society equals two, then it has reached replacement fertility or ZPG. Governments today annually spend a total of $900 million to promote ZPG, mostly in less developed countries. ZPG is also the name of a nongovernmental organization that advocates for population awareness. Its origin in 1968 was inspired by Paul Ehrlich’s Population Bomb.
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 was to have a fertility rate of 2.11. Fertility rate is the average number of children a woman would be expected to have over the course of her life. The replacement fertility is the total fertility rate at which the average women would have one daughter during her life: enough to replace herself. This replacement fertility will depend on mortality rates and the sex ratio at birth. It 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 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.
China is the largest country by population in the world, 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. It is because China’s family planning policy, which was formulated in the early 1970s, 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.
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