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Population is the term typically used to refer to the number of people in a single area. Governments conduct a census to quantify the size of a resident population within a given jurisdiction. The term is also applied to non-human animals, microorganisms, and plants, and has specific uses within such fields as ecology and genetics.



The word population is derived from the Late Latin populationem (a people, a multitude), which itself is derived from the Latin word populus (a people). [1]

Use of the term

Social sciences

Population key Population density key.png
Population key

In sociology and population geography, population refers to a group of human beings with some predefined criterion in common, such as location, race, ethnicity, nationality, or religion.[ citation needed ]


In ecology, a population is a group of organisms of the same species who inhabit the same particular geographical area and are capable of interbreeding. [2] [3] The area of a sexual population is the area where inter-breeding is possible between any pair within the area and more probable than cross-breeding with individuals from other areas. [4]

In ecology, the population of a certain species in a certain area can be estimated using the Lincoln index to calculate the total population of an area based on the number of individuals observed.


Population dynamics is the type of mathematics used to model and study the size and age composition of populations as dynamical systems.


In genetics, a population is often defined as a set of organisms in which any pair of members can breed together. They can thus routinely exchange gametes in order to have usually fertile progeny, and such a breeding group is also known therefore as a gamodeme. This also implies that all members belong to the same species. [5] 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. [6]

This seldom occurs in nature: localization 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 neighboring gamodemes. However, there may be low frequencies of exchange with these neighbors. 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). 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 and animal breeding, procedures have been developed which deliberately utilize the effects of dispersion (such as line breeding, pure-line breeding, backcrossing). 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) [7] and autogamous (self-fertilization) gamodemes. [8]

World human population

According to the UN the world's population surpassed 8 billion on 15 November 2022, [9] a gain of 1 billion since 12 March 2012. According to a separate estimate by the United Nations, Earth's population exceeded seven billion in October 2011. According to UNFPA, growth to such an extent offers unprecedented challenges and opportunities to all of humanity. [10]

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 the world population reached 5 billion in 1987, and six years after the world population reached 5.5 billion in 1993. The population of countries such as Nigeria is not even known to the nearest million, [11] so there is a considerable margin of error in such estimates. [12]

Researcher Carl Haub calculated that a total of over 100 billion people have probably been born in the last 2000 years. [13]

Predicted growth and decline

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). World population growth - time between each billion-person growth.svg
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).

Population growth increased significantly as the Industrial Revolution gathered pace from 1700 onwards. [14] The last 50 years have seen a yet more rapid increase in the rate of population growth [14] due to medical advances and substantial increases in agricultural productivity, particularly beginning in the 1960s, [15] made by the Green Revolution. [16] In 2017 the United Nations Population Division projected that the world's population will reach about 9.8 billion in 2050 and 11.2 billion in 2100. [17]

PRB 2017 Data Sheet Largest Populations PRB 2017 Data Sheet Largest Populations.jpg
PRB 2017 Data Sheet Largest Populations

In the future, the world's population is expected to peak, [18] 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. [19] [20] Population has already declined in the last decade or two in Eastern Europe, the Baltics and in the Commonwealth of Independent States. [21]

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. [22] This transition from high birth and death rates to low birth and death rates is often referred to as the demographic transition. [22]

Population planning

Human population planning is the practice of altering the rate of growth of a human population. Historically, human population control has been implemented with the goal of limiting 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 programs, 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. [23] Growing opposition to the narrow population control focus led to a significant change in population control policies in the early 1980s. [24]

See also

Related Research Articles

<span class="mw-page-title-main">Reproduction</span> Biological process by which new organisms are generated from one or more parent organisms

Reproduction is the biological process by which new individual organisms – "offspring" – are produced from their "parent" or parents. There are two forms of reproduction: asexual and sexual.

<span class="mw-page-title-main">Inbreeding</span> Reproduction by closely related organisms

Inbreeding is the production of offspring from the mating or breeding of individuals or organisms that are closely related genetically. By analogy, the term is used in human reproduction, but more commonly refers to the genetic disorders and other consequences that may arise from expression of deleterious recessive traits resulting from incestuous sexual relationships and consanguinity. Animals avoid incest only rarely.

Small populations can behave differently from larger populations. They are often the result of population bottlenecks from larger populations, leading to loss of heterozygosity and reduced genetic diversity and loss or fixation of alleles and shifts in allele frequencies. A small population is then more susceptible to demographic and genetic stochastic events, which can impact the long-term survival of the population. Therefore, small populations are often considered at risk of endangerment or extinction, and are often of conservation concern.

Population genetics is a subfield of genetics that deals with genetic differences within and among populations, and is a part of evolutionary biology. Studies in this branch of biology examine such phenomena as adaptation, speciation, and population structure.

<span class="mw-page-title-main">Family planning</span> Planning when to have children

Family planning is the consideration of the number of children a person wishes to have, including the choice to have no children, and the age at which they wish to have them. Things that may play a role on family planning decisions include marital situation, career or work considerations, financial situations. If sexually active, family planning may involve the use of contraception and other techniques to control the timing of reproduction.

Genetic linkage is the tendency of DNA sequences that are close together on a chromosome to be inherited together during the meiosis phase of sexual reproduction. Two genetic markers that are physically near to each other are unlikely to be separated onto different chromatids during chromosomal crossover, and are therefore said to be more linked than markers that are far apart. In other words, the nearer two genes are on a chromosome, the lower the chance of recombination between them, and the more likely they are to be inherited together. Markers on different chromosomes are perfectly unlinked, although the penetrance of potentially deleterious alleles may be influenced by the presence of other alleles, and these other alleles may be located on other chromosomes than that on which a particular potentially deleterious allele is located.

<span class="mw-page-title-main">Quantitative genetics</span> Study of the inheritance of continuously variable traits

Quantitative genetics is the study of quantitative traits, which are phenotypes that vary continuously—such as height or mass—as opposed to phenotypes and gene-products that are discretely identifiable—such as eye-colour, or the presence of a particular biochemical.

Fecundity is defined in two ways; in human demography, it is the potential for reproduction of a recorded population as opposed to a sole organism, while in population biology, it is considered similar to fertility, the natural capability to produce offspring, measured by the number of gametes (eggs), seed set, or asexual propagules.

The effective population size (Ne) is size of an idealised population would experience the same rate of genetic drift or increase in inbreeding as in the real population. Idealised populations are based on unrealistic but convenient assumptions including random mating, simultaneous birth of each new generation, constant population size. For most quantities of interest and most real populations, Ne is smaller than the census population size N of a real population. The same population may have multiple effective population sizes for different properties of interest, including genetic drift and inbreeding.

<span class="mw-page-title-main">Minimum viable population</span> Smallest size a biological population can exist without facing extinction

Minimum viable population (MVP) is a lower bound on the population of a species, such that it can survive in the wild. This term is commonly used in the fields of biology, ecology, and conservation biology. MVP refers to the smallest possible size at which a biological population can exist without facing extinction from natural disasters or demographic, environmental, or genetic stochasticity. The term "population" is defined as a group of interbreeding individuals in similar geographic area that undergo negligible gene flow with other groups of the species. Typically, MVP is used to refer to a wild population, but can also be used for ex situ conservation.

<span class="mw-page-title-main">Conservation genetics</span> Interdisciplinary study of extinction avoidance

Conservation genetics is an interdisciplinary subfield of population genetics that aims to understand the dynamics of genes in a population for the purpose of natural resource management, conservation of genetic diversity, and the prevention of species extinction. Scientists involved in conservation genetics come from a variety of fields including population genetics, research in natural resource management, molecular ecology, molecular biology, evolutionary biology, and systematics. The genetic diversity within species is one of the three fundamental components of biodiversity, so it is an important consideration in the wider field of conservation biology.

Plant breeders use different methods depending on the mode of reproduction of crops, which include:

<span class="mw-page-title-main">Estimates of historical world population</span> Estimates of historical world population

This article lists current estimates of the world population in history. In summary, estimates for the progression of world population since the Late Middle Ages are in the following ranges:

Panmixia means uniform random fertilization. A panmictic population is one where all potential parents may contribute equally to the gamete pool, and that these gametes are uniformly distributed within the gamete population (gamodeme). This assumes that there are no hybridising restrictions within the parental population : neither genetics, cytogenetics nor behavioural; and neither spatial nor temporal. Therefore, all gamete recombination (fertilization) is uniformly possible. Both the Wahlund effect and the Hardy Weinberg equilibrium assume that the overall population is panmictic.

<span class="mw-page-title-main">World population</span> Total number of living humans on Earth

In world demographics, the world population is the total number of humans currently living. It was estimated by the United Nations to have exceeded eight billion in mid-November 2022. It took around 300,000 years of human prehistory and history for the human population to reach one billion and only 222 years more to reach 8 billion.

Reproductive compensation was originally a theory to explain why recessive genetic disorders may persist in a population. It was proposed in 1967 as an explanation for the maintenance of Rh negative blood groups. Reproductive compensation refers to the tendency of parents, seeking a given family size, to replace offspring that are lost to genetic disorders. It may also refer to the effects of increased maternal or parental investment in caring for disadvantaged offspring, seeking to compensate for genetic disadvantage. It is a theory that suggests that behavioral as well as physiological factors may play a role in the level of recessive genetic disorders in a population.

Inbreeding avoidance, or the inbreeding avoidance hypothesis, is a concept in evolutionary biology that refers to the prevention of the deleterious effects of inbreeding. Animals only rarely exhibit inbreeding avoidance. The inbreeding avoidance hypothesis posits that certain mechanisms develop within a species, or within a given population of a species, as a result of assortative mating and natural and sexual selection, in order to prevent breeding among related individuals. Although inbreeding may impose certain evolutionary costs, inbreeding avoidance, which limits the number of potential mates for a given individual, can inflict opportunity costs. Therefore, a balance exists between inbreeding and inbreeding avoidance. This balance determines whether inbreeding mechanisms develop and the specific nature of such mechanisms.

In population genetics, the allele frequency spectrum, sometimes called the site frequency spectrum, is the distribution of the allele frequencies of a given set of loci in a population or sample. Because an allele frequency spectrum is often a summary of or compared to sequenced samples of the whole population, it is a histogram with size depending on the number of sequenced individual chromosomes. Each entry in the frequency spectrum records the total number of loci with the corresponding derived allele frequency. Loci contributing to the frequency spectrum are assumed to be independently changing in frequency. Furthermore, loci are assumed to be biallelic, although extensions for multiallelic frequency spectra exist.

Autogamy or self-fertilization refers to the fusion of two gametes that come from one individual. Autogamy is predominantly observed in the form of self-pollination, a reproductive mechanism employed by many flowering plants. However, species of protists have also been observed using autogamy as a means of reproduction. Flowering plants engage in autogamy regularly, while the protists that engage in autogamy only do so in stressful environments.

This glossary of genetics and evolutionary biology is a list of definitions of terms and concepts used in the study of genetics and evolutionary biology, as well as sub-disciplines and related fields, with an emphasis on classical genetics, quantitative genetics, population biology, phylogenetics, speciation, and systematics. Overlapping and related terms can be found in Glossary of cellular and molecular biology, Glossary of ecology, and Glossary of biology.


  1. "population | Etymology, origin and meaning of population by etymonline". www.etymonline.com. Retrieved 8 June 2023.
  2. "Population". Biology Online. Retrieved 5 December 2012.
  3. "Definition of population (biology)". Oxford Dictionaries. Oxford University Press. Archived from the original on 10 May 2013. Retrieved 5 December 2012. a community of animals, plants, or humans among whose members interbreeding occurs
  4. Hartl, Daniel (2007). Principles of Population Genetics. Sinauer Associates. p. 45. ISBN   978-0-87893-308-2.
  5. Hartl, Daniel (2007). Principles of Population Genetics. Sinauer Associates. p. 95. ISBN   978-0-87893-308-2.
  6. Fisher, R. A. (1999). The Genetical Theory of Natural Selection. Oxford University Press (OUP). ISBN   978-0-19-850440-5.
  7. Gordon, Ian L. (2000). "Quantitative genetics of allogamous F2 : an origin of randomly fertilized populations". Heredity . 85: 43–52. doi: 10.1046/j.1365-2540.2000.00716.x . PMID   10971690.
  8. Gordon, Ian L. (2001). "Quantitative genetics of autogamous F2". Hereditas . 134 (3): 255–262. doi: 10.1111/j.1601-5223.2001.00255.x . PMID   11833289.
  9. "Population Clock". www.worldometers.info. Archived from the original on 15 November 2022. Retrieved 15 November 2022.
  10. to a World of Seven Billion People Archived 13 January 2012 at the Wayback Machine UNFPA 12 September 2011
  11. "Cities in Nigeria: 2005 Population Estimates – MongaBay.com" . Retrieved 1 July 2008.
  12. "Country Profile: Nigeria". BBC News. 24 December 2009. Retrieved 1 July 2008.
  13. Haub, C. 1995/2004. "How Many People Have Ever Lived on Earth?" Population Today, "How Many People Have Ever Lived on Earth? - Population Reference Bureau". Archived from the original on 24 April 2013. Retrieved 29 April 2013.
  14. 1 2 As graphically illustrated by population since 10,000BC and population since 1000AD
  15. "The end of India's green revolution?". BBC News. 29 May 2006. Retrieved 29 November 2009.
  16. Food First/Institute for Food and Development Policy Archived 14 July 2009 at the Wayback Machine
  17. "UN Population Prospects 2017" (PDF).
  18. World Population Development Statistics: Forecast, United Nations, 2011.
  19. Lutz, Wolfgang; Sanderson, Warren; Scherbov, Sergei (2001). "The End of World Population Growth" (PDF). Nature. 412 (6846): 543–545. Bibcode:2001Natur.412..543L. doi:10.1038/35087589. PMID   11484054. S2CID   4425080.
  20. Ojovan, M.I.; Loshchinin, M.B. (2015). "Heuristic Paradoxes of S.P. Kapitza Theoretical Demography". European Researcher. 92 (3): 237–248. doi: 10.13187/er.2015.92.237 .
  21. "world demographic trends". gsociology.icaap.org. Retrieved 18 July 2019.
  22. 1 2 "Human Population Growth". Archived from the original on 30 March 2009. Retrieved 7 April 2009.
  23. Knudsen, Lara (2006). Reproductive Rights in a Global Context . Vanderbilt University Press. pp.  2. ISBN   978-0-8265-1528-5. reproductive rights.
  24. Knudsen, Lara (2006). Reproductive Rights in a Global Context . Vanderbilt University Press. pp.  4–5. ISBN   978-0-8265-1528-5. reproductive rights.

Further reading