View source for Population

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[[File:Population density.png|thumb|346px|The distribution of human [[world population]] in 1994]]
[[File:Population density key.png|thumb|150px|Key]]
A '''population''' is the number of all the [[organism]]s of the same group or [[species]], which live in a particular [[geographical area]], and have the capability of interbreeding.<ref>{{cite web |title=Population |url=http://www.biology-online.org/dictionary/Population|publisher=Biology Online |accessdate=5 December 2012}}</ref><ref>{{cite web |title=Definition of population (biology) |url=http://oxforddictionaries.com/definition/english/population?q=population |work=Oxford Dictionaries |publisher=Oxford University Press |accessdate=5 December 2012 |quote=a community of animals, plants, or humans among whose members interbreeding occurs}}</ref>

The area that is used to define a [[sex]]ual population is defined as the area where [[interbreeding|inter-breeding]] is potentially possible between any pair within the area, and where the probability of interbreeding is greater than the probability of [[Crossbreed|cross-breeding]] with individuals from other areas.<ref>{{cite book | last=Hartl | first=Daniel | title=Principles of Population Genetics | publisher=[[Sinauer Associates]] | series=| year=2007 | isbn=978-0-87893-308-2 | page=45}}</ref>

In [[sociology]], population refers to a collection of [[human]]s. [[Demography]] is a [[social science]] which entails the statistical study of human populations. This article refers mainly to human population.

==Population genetics (ecology)==
In [[population genetics]] a sexual population is a set of organisms in which any pair of members can [[Breeding in the wild|breed]] together. This means that they can regularly exchange gametes to produce normally-fertile offspring, and such a breeding group is also known therefore as a ''gamodeme''. This also implies that all members belong to the same species.<ref>{{cite book | last=Hartl | first=Daniel | title=Principles of Population Genetics | publisher=[[Sinauer Associates]] | year=2007 | isbn=978-0-87893-308-2 | page=95}}</ref>
If the gamodeme is very large (theoretically, approaching infinity), and all gene alleles are uniformly distributed by the gametes within it, the gamodeme is said to be panmictic. Under this state, [[allele]] ([[gamete]]) frequencies can be converted to genotype ([[zygote]]) frequencies by expanding an appropriate [[quadratic equation]], as shown by Sir [[Ronald Fisher]] in his establishment of quantitative genetics.<ref>{{cite book | last=Fisher | first=R. A. | title=The Genetical Theory of Natural Selection | publisher=[[Oxford University Press]] | year=1999 | isbn=0-19-850440-3}}</ref>

This seldom occurs in nature: localisation of gamete exchange – through dispersal limitations, preferential mating, cataclysm, or other cause – may lead to small actual gamodemes which exchange gametes reasonably uniformly within themselves, but are virtually separated from their neighbouring gamodemes. However, there may be low frequencies of exchange with these neighbours. This may be viewed as the breaking up of a large sexual population (panmictic) into smaller overlapping sexual populations. This failure of [[panmixia]] leads to two important changes in overall population structure: (1) the component gamodemes vary (through gamete sampling) in their allele frequencies when compared with each other and with the theoretical panmictic original (this is known as ''dispersion'', and its details can be estimated using expansion of an appropriate [[binomial equation]]); and (2) the level of homozygosity rises in the entire collection of gamodemes. The overall rise in homozygosity is quantified by the ''inbreeding coefficient'' (''f'' or ''φ''). Note that ''all homozygotes'' are increased in frequency – both the deleterious and the desirable. The mean phenotype of the gamodemes collection is lower than that of the panmictic "original" – which is known as ''inbreeding depression''. It is most important to note, however, that some dispersion lines will be superior to the panmictic original, while some will be about the same, and some will be inferior. The probabilities of each can be estimated from those binomial equations. In [[plant breeding|plant]] and [[animal breeding]], procedures have been developed which deliberately utilise the effects of dispersion (such as line breeding, pure-line breeding, back-crossing). It can be shown that ''dispersion-assisted selection'' leads to the greatest ''genetic advance'' (''ΔG''=change in the phenotypic mean), and is much more powerful than selection acting without attendant dispersion. This is so for both allogamous (random fertilization)<ref>{{cite journal | last=Gordon  | first=Ian L. | title=Quantitative genetics of allogamous F2 : an origin of randomly fertilized populations | journal=Heredity   | year=2000  | volume=85  | pages=43–52  | doi=10.1046/j.1365-2540.2000.00716.x  | pmid=10971690}}</ref> and autogamous (self-fertilization) gamodemes.<ref>{{cite journal | last=Gordon  | first=Ian L. | title=Quantitative genetics of autogamous F2 | journal=Hereditas | year=2001 | volume=134 | pages=255–262 | doi=10.1111/j.1601-5223.2001.00255.x | pmid=11833289 | issue=3}}</ref>

In ecology, the population of a certain species in a certain area can be estimated using the [[Lincoln Index]].

== World human population ==
{{Main|World population}}

As of today's date, the world population is [[Guesstimate|estimated]] by the [[United States Census Bureau]] to be {{#expr:({{data world|poptoday}}/1000000000) round 3}} [[1,000,000,000|billion]].<ref>[http://www.census.gov/ipc/www/popclockworld.html U.S. Census Bureau – World Pop Clock Projection]</ref> The US Census Bureau estimates the 7 billion number was surpassed on 12 March 2012. According to a separate estimate by the United Nations, Earth’s population exceeded seven billion in October 2011, a milestone that offers unprecedented challenges and opportunities to all of humanity, according to [[UNFPA]], the United Nations Population Fund.<ref>[http://www.unfpa.org/public/home/news/pid/8328Countdown to a World of Seven Billion People] [[UNFPA]] 12.9.2011</ref>

According to papers published by the United States Census Bureau, the world population hit 6.5 billion 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 countries such as [[Nigeria]], is not even known to the nearest million,<ref>{{cite web |url=http://www.mongabay.com/igapo/2005_world_city_populations/Nigeria.html | title=Cities in Nigeria: 2005 Population Estimates&nbsp;– MongaBay.com |accessdate=1 July 2008}}</ref> so there is a considerable margin of error in such estimates.<ref>{{cite web |url=http://news.bbc.co.uk/2/hi/africa/country_profiles/1064557.stm |title=Country Profile: Nigeria |accessdate=1 July 2008 | work=BBC News | date=24 December 2009}}</ref>

Researcher Carl Haub calculated that a total of over 100 billion people have probably been born in the last 2000 years.<ref>Haub, C. 1995/2004. "How Many People Have Ever Lived On Earth?" Population Today, http://www.prb.org/Articles/2002/HowManyPeopleHaveEverLivedonEarth.aspx</ref>

=== Predicted growth and decline ===
[[File:World population growth - time between each billion-person growth.jpg|550px|thumb|The years taken for every billion people to be added to the world's population, and the years that population was reached (with future estimates).]]
{{Main|Population growth}}

[[Population growth]] increased significantly as the [[Industrial Revolution]] gathered pace from 1700 onwards.<ref name="historic population graphs">As graphically illustrated by [[:File:Poulation-since-10000BC.jpg|population since 10,000BC]] and [[:File:Poulation-since-1000AD.jpg|population since 1000AD]]</ref> The last 50 years have seen a yet more rapid increase in the [[Population growth#Population growth rate|rate]] of population growth<ref name=" historic population graphs " /> due to [[History of medicine#Modern medicine|medical advances]] and substantial increases in agricultural productivity, particularly beginning in the 1960s,<ref>{{Cite news |url=http://news.bbc.co.uk/1/hi/world/south_asia/4994590.stm |work=BBC News |title=The end of India's green revolution? |date=29 May 2006 |accessdate=29 November 2009 }}</ref> made by the [[Green Revolution]].<ref>[http://www.foodfirst.org/media/opeds/2000/4-greenrev.html Food First/Institute for Food and Development Policy]</ref> In 2007 the [[United Nations Population Division]] projected that the world's population will likely surpass 10 billion in 2055.<ref>{{cite press release |title=World population will increase by 2.5 billion by 2050; people over 60 to increase by more than 1 billion|publisher=United Nations Population Division |date=13 March 2007 |url= http://www.un.org/News/Press/docs/2007/pop952.doc.htm |accessdate=14 March 2007 |quote=The world population continues its path towards population ageing and is on track to surpass 9 billion persons by 2050.}}</ref>

In the future, the world's population is expected to peak,<ref>[http://www.statista.com/statistics/1717/forecast-about-the-development-of-the-world-population/ World Population Development Statistics: Forecast], United Nations, 2011.</ref> after which it will decline due to economic reasons, health concerns, land exhaustion and environmental hazards. According to one report, it is very likely that the world's population will stop growing before the end of the 21st century. Further, there is some likelihood that population will actually decline before 2100.<ref>{{cite web |url=http://www.nature.com/nature/journal/v412/n6846/full/412543a0.html |title= The End of World Population Growth |accessdate=4 November 2008}}</ref><ref>Ojovan M.I., Loshchinin M.B. Heuristic Paradoxes of S.P. Kapitza Theoretical Demography. European Researcher, 92 (3), 237-248 (2015). http://www.erjournal.ru/journals_n/1427563722.pdf (2015)</ref> Population has already declined in the last decade or two in Eastern Europe, the Baltics and in the Commonwealth of Independent States.<ref>Shackman, Gene, Xun Wang and Ya-Lin Liu. 2011.  Brief review of world population trends.  Available at http://gsociology.icaap.org/report/demsum.html</ref>

The population pattern of less-developed regions of the world in recent years has been marked by gradually declining birth rates. These followed an earlier sharp reduction in death rates.<ref name="users.rcn.com">http://users.rcn.com/jkimball.ma.ultranet/BiologyPages/P/Populations.html</ref> This transition from high birth and death rates to low birth and death rates is often referred to as the [[demographic transition]].<ref name="users.rcn.com"/>

=== Control ===
{{Main|Human population control}}

Human population control is the practice of altering the rate of growth of a human population. Historically, human  population control has been implemented with the goal of increasing the rate of population growth. 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 population growth rates. While population control can involve measures that improve people's lives by giving them greater control of their reproduction, a few programmes, most notably the Chinese government's one-child per family policy, have resorted to coercive measures.

In the 1970s, 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.<ref>{{cite book |title=Reproductive Rights in a Global Context |last= Knudsen |first=Lara |authorlink= |author2= |year=2006 |publisher= Vanderbilt University Press |isbn=9780826515285 |pages=2 |url=https://books.google.com/?id=b3thCcdyScsC&dq=reproductive+rights }}</ref> Growing opposition to the narrow population control focus led to a significant change in population control policies in the early 1980s.<ref>{{cite book |title=Reproductive Rights in a Global Context |last= Knudsen |first=Lara |authorlink= |author2= |year=2006 |publisher= Vanderbilt University Press |location= |isbn=9780826515285 |pages=4–5 |url=https://books.google.com/?id=b3thCcdyScsC&dq=reproductive+rights }}</ref>

==See also==
* [[Community (ecology)]]
* [[List of countries by population]]
* [[Lists of organisms by population]]

==References==
{{Reflist|30em}}

==External links==
{{Wikidata property |1=P1082 |2=population }}
* [http://www.unfpa.org UNFPA, The United Nations Population Fund]
* [http://www.un.org/esa/population/unpop.htm United Nations Population Division]
* [http://www.cicred.org/Eng/Publications/IndexPublications.htm CICRED homepage] a platform for interaction between research centres and international organizations, such as the United Nations Population Division, [[UNFPA]], [[WHO]] and [[FAO]].
* [http://www.census.gov/ipc/www/popclockworld.html Current World Population]
* [http://www.necsp.org NECSP HomePage]
* [http://www.overpopulation.info Overpopulation]
* [http://www.optimumpopulation.org Population Matters]
* [http://www.prb.org Population Reference Bureau] (2005). Retrieved 13 February 2005.
* [http://www.populationworld.com/ Population World: Population of World]. Retrieved 13 February 2004.
* [http://www.sieds.it/index_en.htm SIEDS, Italian Society of Economics Demography and Statistics]
* [http://www.unece.org/pau United Nations Economic Commission for Europe – Official Web Site]
* [http://www.counttheworld.com/?counter=pop_world World Population Counter, and separate regions.]
* [http://www.worldpopclock.com WorldPopClock.com]. (French)
* [http://www.populationsdumonde.com Populations du monde]. (French)
* [http://stats.oecd.org/wbos/Index.aspx?QueryId=254 OECD population data]
* [http://gsociology.icaap.org/  Understanding the World Today] Reports about world and regional population trends
* {{cite encyclopedia |last1=Lee |first1=Ronald Demos |authorlink1= |last2= |first2= |authorlink2= |editor=[[David R. Henderson]] (ed.) |encyclopedia=[[Concise Encyclopedia of Economics]] |title=Population |url=http://www.econlib.org/library/Enc/Population.html |year=2008 |edition= 2nd |publisher=[[Library of Economics and Liberty]] |location=Indianapolis |isbn=978-0865976658 |oclc=237794267}}

{{Population}}
{{Population country lists}}
{{biological organisation}}
{{Ethnicity}}
{{Use dmy dates|date=August 2010}}

{{Authority control}}

[[Category:Population| ]]
[[Category:Population ecology]]
[[Category:Lists by population|Countries]]
[[Category:Population models]]
[[Category:Demography]]