For other uses, see Population (disambiguation). Distribution of world population in 1994. A population is all the organisms that both belong to the same species and live in the same geographical area. The area that is used to define the population is such that inter-breeding is possible between any pair within the area and more probable than cross-breeding with individuals from other areas. Normally breeding is substantially more common within the area than across the border.1 In sociology, population refers to a collection of human beings. Demography is a sociological discipline which entails the statistical study of human populations. This article refers mainly to human population. Contents 1 Population genetics 2 World human population 2.1 Growth 2.2 Control 3 See also 4 Notes 5 External links Population genetics In population genetics a population is a set of organisms in which any pair of members can breed together. This implies that all members belong to the same species and live near each other.2 . World human population Main article: World population

As of 19 February 2011, the world population is estimated by the United States Census Bureau to be 6.901 billion.3 According to papers published by the United States Census Bureau, the world population hit 6.5 billion (6,500,000,000) on 24 February 2006. The United Nations Population Fund designated 12 October 1999 as the approximate day on which world population reached 6 billion. This was about 12 years after world population reached 5 billion in 1987, and 6 years after world population reached 5.5 billion in 1993. The population of some countries, such as Nigeria and China is not even known to the nearest million,4 so there is a considerable margin of error in such estimates.5 Growth Time taken for each billion people to be added to the world's population (including future estimates). See also alt. chart Main article: population growth Population growth increased significantly as the Industrial Revolution gathered pace from 1700 onwards.6 The last 50 years have seen a yet more rapid increase in the rate of population growth6 due to medical advances and substantial increases in agricultural productivity, particularly beginning in the 1960s,7 made by the Green Revolution.8 In 2007 the United Nations Population Division projected that the world's population will likely surpass 10 billion in 2055.9 In the future, world population has been expected to reach a peak of growth, from there it will decline due to economic reasons, health concerns, land exhaustion and environmental hazards. There is around an 85% chance that the world's population will stop growing before the end of the century.citation needed There is a 60% probability that the world's population will not exceed 10 billion people before 2100, and around a 15% probability that the world's population at the end of the century will be lower than it is today. For different regions, the date and size of the peak population will vary considerably.10

The population pattern of less-developed regions of the world in recent years has been marked by gradually declining birth rates following an earlier sharp reduction in death rates.11 This transition from high birth and death rates to low birth and death rates is often referred to as the demographic transition.11 Control Main article: Human population control Human population control is the practice of artificially altering the rate of growth of a human population. Historically, human population control has been implemented by limiting the population's birth rate, usually by government mandate, and has been undertaken as a response to factors including high or increasing levels of poverty, environmental concerns, religious reasons, and overpopulation. While population control can involve measures that improve people's lives by giving them greater control of their reproduction, some programs have exposed them to exploitation.12 Worldwide, the population control movement was active throughout the 1960s and 1970s, driving many reproductive health and family planning programs. In the 1980s, tension grew between population control advocates and women's health activists who advanced women's reproductive rights as part of a human rights-based approach.13 Growing opposition to the narrow population control focus led to a significant change in population control policies in the early 1990s.14 See also Crude birth rate Crude death rate Demography Life expectancy Median age Net migration rate Mortality under age 5 Net migration Net reproduction rate Nurgaliev's law Overpopulation Population change Population density Population growth rate Rate of natural increase Sex ratio Rural area Urban population World population Zero population growth

Lists: List of countries by fertility rate List of countries by population List of countries by population density List of religious populations World's largest cities Population economics: Demographic economics Dependency ratios Non-human specific: Animal population control Biological dispersal Biological exponential growth Overpopulation in companion animals Overpopulation in wild animals Population ecology Notes ^ Hartl, Daniel (2007). Principles of Population Genetics. Sinauer Associates. p. 45. ISBN 978-0-87893-308-2.  ^ Hartl, Daniel (2007). Principles of Population Genetics. Sinauer Associates. p. 95. ISBN 978-0-87893-308-2.  ^ U.S. Census Bureau - World POPClock Projection ^ "Cities in Nigeria: 2005 Population Estimates — MongaBay.com". http://www.mongabay.com/igapo/2005_world_city_populations/Nigeria.html. Retrieved 1 July 2008.  ^ "Country Profile: Nigeria". BBC News. 24 December 2009. http://news.bbc.co.uk/2/hi/africa/country_profiles/1064557.stm. Retrieved 1 July 2008.  ^ a b As graphically illustrated by population since 10,000BC and population since 1000AD ^ "The end of India's green revolution?". BBC News. 29 May 2006. http://news.bbc.co.uk/1/hi/world/south_asia/4994590.stm. Retrieved 29 November 2009.  ^ Food First/Institute for Food and Development Policy ^ United Nations Population Division (13 March 2007). "World population will increase by 2.5 billion by 2050; people over 60 to increase by more than 1 billion". Press release. http://www.un.org/News/Press/docs/2007/pop952.doc.htm. Retrieved 14 March 2007. "The world population continues its path towards population ageing and is on track to surpass 9 billion persons by 2050."  ^ "The End of World Population Growth". http://www.nature.com/nature/journal/v412/n6846/full/412543a0.html. Retrieved 4 November 2008.  ^ a b http://users.rcn.com/jkimball.ma.ultranet/BiologyPages/P/Populations.html ^ Populationconcern.org.uk ^ Knudsen, Lara (2006). Reproductive Rights in a Global Context. Vanderbilt University Press. pp. 2. ISBN 0826515282, 9780826515285. http://books.google.com/books?id=b3thCcdyScsC&dq=reproductive+rights&source=gbs_summary_s&cad=0.  ^ Knudsen, Lara (2006). Reproductive Rights in a Global Context. Vanderbilt University Press. pp. 4–5. ISBN 0826515282, 9780826515285. http://books.google.com/books?id=b3thCcdyScsC&dq=reproductive+rights&source=gbs_summary_s&cad=0.  External links UNFPA, The United Nations Population Fund United Nations Population Division CICRED homepage a platform for interaction between research centres and international organizations, such as the United Nations Population Division, UNFPA, WHO and FAO. Current World Population NECSP HomePage Overpopulation Population and Health InfoShare. Retrieved 13 February 2005. Population in the news homepage Optimum Population Trust Gallery: The World's Ten Most Populous Countries Retrieved 13 May 2009. Population Reference Bureau (2005). Retrieved 13 February 2005. Population World: Population of World. Retrieved 13 February 2004. PopulationData.net - Information and maps about populations around the world. Retrieved 4 March 2005. PopulationData.net (2005). SIEDS, Italian Society of Economics Demography and Statistics United Nations (2004). Population Division, Department of Economic and Social Affairs. Retrieved 13 February 2004. United Nations Economic Commission for Europe - Official Web Site United States Census Bureau (2005). Census Bureau - Countries Ranked by Population. Retrieved 13 February 2005. World Population Counter, and separate regions. WorldPopClock.com. (French) Populations du monde. (French) OECD population data v · d · eTopics on human population Major articles World population · Family planning · Green revolution · Overpopulation · Over-consumption (water crisis) · Reproductive rights  · Sustainable development Biological topics Population biology · Population control (one-child policy · Immigration reduction) · Population decline · Population density (physiological density) · Population growth · Population pyramid Population ecology Carrying capacity · Ecological footprint · I = P • A • T · Malthusian growth model · World3 model · Food security · World energy resources and consumption · Habitat destruction · Optimum population Literary works A Modest Proposal · An Essay on the Principle of Population · Operating Manual for Spaceship Earth · How Much Land Does a Man Need? · The Limits to Growth · The Population Bomb · The Ultimate Resource · The Skeptical Environmentalist Lists Most highly populated countries · Metropolitan areas by population Events and organizations International Conference on Population and Development  · Optimum Population Trust  · United Nations Population Fund · World Population Foundation Related articles World Population Day · "The Day of Six Billion" · Easter Island downfall · Classic Maya collapse · Holocene extinction · Fertility and intelligence v · d · eHierarchy of life Biosphere >  Ecosystem > Community (Biocoenosis) > Population >  Organism > Organ system > Organ > Tissue > Cell > Organelle > Molecule (Macromolecule · Biomolecule) > Atom