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In biology, a population is a
number A number is a mathematical object used to count, measure, and label. The original examples are the natural numbers 1, 2, 3, 4, and so forth. Numbers can be represented in language with number words. More universally, individual numbers can be re ...
of all the
organism In biology, an organism (from Greek: ὀργανισμός, ''organismos'') is any individual contiguous system that embodies the properties of life. It is a synonym for "life form". Organisms are classified by taxonomy into groups such as ...
s of the same group or
species In biology, a species is the basic unit of classification and a taxonomic rank of an organism, as well as a unit of biodiversity. A species is often defined as the largest group of organisms in which any two individuals of the appropriate sexe ...
who live in a particular
geographical area A geographic coordinate system (GCS) is a coordinate system associated with positions on Earth (geographic position). A GCS can give positions: *as spherical coordinate system using latitude, longitude, and elevation; *as map coordinates p ...
and are capable of
interbreeding In biology, a hybrid is the offspring resulting from combining the qualities of two organisms of different breeds, varieties, species or genera through sexual reproduction. Hybrids are not always intermediates between their parents (such as in b ...
. 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 A crossbreed is an organism with purebred parents of two different breeds, varieties, or populations. ''Crossbreeding'', sometimes called "designer crossbreeding", is the process of breeding such an organism, While crossbreeding is used to mainta ...
with individuals from other areas. In
sociology Sociology is the study of society, human social behaviour, patterns of social relationships, social interaction, and culture that surrounds everyday life. It is a social science that uses various methods of empirical investigation and critical ...
, population refers to a collection of
human Humans (''Homo sapiens'') are the most populous and widespread species of primates, characterized by bipedality, opposable thumbs, hairlessness, and intelligence allowing the use of culture, language and tools. They are the only extant members ...

human
s.
Demography Demography (from prefix ''demo-'' from Ancient Greek δῆμος (''dēmos'') meaning 'the people', and ''-graphy'' from γράφω (''graphō'') meaning 'writing, description or measurement') is the statistical study of populations, especiall ...
is a
social science#REDIRECT Social science#REDIRECT Social science {{Redirect category shell, 1= {{R from other capitalisation ...
{{Redirect category shell, 1= {{R from other capitalisation ...
which entails the statistical study of populations. Population, in simpler terms, is the number of people in a city or town, region, country or world; population is usually determined by a process called census (a process of collecting, analyzing, compiling and publishing data).


Population genetics (ecology)

In
population genetics#REDIRECT population genetics#REDIRECT population genetics {{R from other capitalisation ...
{{R from other capitalisation ...
a sexual population is a set of organisms in which any pair of members can
breed A breed is a specific group of domestic animals having homogeneous appearance (phenotype), homogeneous behavior, and/or other characteristics that distinguish it from other organisms of the same species. In literature, there exist several slightl ...
together. This means that they can regularly exchange gametes to produce normally-fertile offspring, and such a
breeding Breeding is sexual reproduction that produces offspring, usually animals or plants. It can only occur between a male and a female animal or plant. Breeding may refer to: * Breeding in the wild, the natural process of reproduction in the animal kin ...
group is also known therefore as a ''gamodeme''. This also implies that all members belong to the same species. 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 An allele (, ; ; modern formation from Greek ἄλλος ''állos'', "other") is one of two, or more, forms of a given gene variant. For example, the ABO blood grouping is controlled by the ABO gene, which has six common alleles. Nearly every liv ...
(
gamete A gamete (/ˈɡæmiːt/; from Ancient Greek γαμετή ''gamete'' from gamein "to marry") is a haploid cell that fuses with another haploid cell during fertilization in organisms that reproduce sexually. Gametes are an organism's reproductive cel ...
) frequencies can be converted to genotype (
zygote A zygote (from Greek ζυγωτός ''zygōtos'' "joined" or "yoked", from ζυγοῦν ''zygoun'' "to join" or "to yoke") is a eukaryotic cell formed by a fertilization event between two gametes. The zygote's genome is a combination of the D ...
) frequencies by expanding an appropriate
quadratic equation In algebra, a quadratic equation (from the Latin for "square") is any equation that can be rearranged in standard form as :ax^2 + bx + c = 0 where represents an unknown, and , , and represent known numbers, where . If , then the equation is l ...
, as shown by Sir
Ronald Fisher Sir Ronald Aylmer Fisher (17 February 1890 – 29 July 1962) was a British statistician, geneticist, and academic. For his work in statistics, he has been described as "a genius who almost single-handedly created the foundations for modern ...
in his establishment of quantitative genetics. 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 Panmixia (or panmixis) means random mating. A panmictic population is one where all individuals are potential partners. This assumes that there are no mating restrictions, neither genetic nor behavioural, upon the population and that therefore all ...
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 In algebra, a binomial is a polynomial that is the sum of two terms, each of which is a monomial. It is the simplest kind of polynomial after the monomials. Definition A binomial is a polynomial which is the sum of two monomials. A binomial in a s ...
); 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 Plants are mainly multicellular organisms, predominantly photosynthetic eukaryotes of the kingdom Plantae. Historically, plants were treated as one of two kingdoms including all living things that were not animals, and all algae and fungi wer ...
and
animal breeding Animal breeding is a branch of animal science that addresses the evaluation (using best linear unbiased prediction and other methods) of the genetic value (estimated breeding value, EBV) of livestock. Selecting for breeding animals with superior EBV ...
, 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) and autogamous (self-fertilization) gamodemes. In ecology, the population of a certain species in a certain area can be estimated using the
Lincoln Index The Lincoln index is a statistical measure used in several fields to estimate the number of cases that have not yet been observed, based on two independent sets of observed cases. Described by Frederick Charles Lincoln in 1930, it is also sometimes ...
.


World human population

According to the
United States Census Bureau The United States Census Bureau (USCB), officially the Bureau of the Census, is a principal agency of the U.S. Federal Statistical System, responsible for producing data about the American people and economy. The Census Bureau is part of the U. ...
the world's population was about 7.55 billion in 2019 and that 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 (UNFPA), formerly the United Nations Fund for Population Activities, is a UN agency aimed at improving reproductive and maternal health worldwide. Its work includes developing national healthcare strategies and ...
. 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 The United Nations Population Fund (UNFPA), formerly the United Nations Fund for Population Activities, is a UN agency aimed at improving reproductive and maternal health worldwide. Its work includes developing national healthcare strategies and ...
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 Nigeria (), officially the Federal Republic of Nigeria, is a country in West Africa. It borders Niger in the north, Chad in the northeast, Cameroon in the east, and Benin in the west. Its southern coast is on the Gulf of Guinea in the Atlanti ...
is not even known to the nearest million, so there is a considerable margin of error in such estimates. Researcher Carl Haub calculated that a total of over 100 billion people have probably been born in the last 2000 years.


Predicted growth and decline

Population growth Population growth is the increase in the number of individuals in a population. Global human population growth amounts to around 83 million annually, or 1.1% per year. The global population has grown from 1 billion in 1800 to 7.9 billion in 2020. T ...
increased significantly as the
Industrial Revolution The Industrial Revolution was the transition to new manufacturing processes in Europe and the United States, in the period from about 1760 to sometime between 1820 and 1840. This transition included going from hand production methods to machin ...
gathered pace from 1700 onwards.As graphically illustrated by population since 10,000BC and population since 1000AD The last 50 years have seen a yet more rapid increase in the
rate Rate or rates may refer to: Finance * Rates (tax), a type of taxation system in the United Kingdom used to fund local government * Exchange rate, rate at which one currency will be exchanged for another Mathematics and science * Rate (mathemat ...
of population growth due to medical advances and substantial increases in agricultural productivity, particularly beginning in the 1960s, made by the
Green Revolution The Green Revolution, or the Third Agricultural Revolution, is the set of research technology transfer initiatives occurring between 1950 and the late 1960s, that increased agricultural production worldwide, beginning most markedly in the late ...
. In 2017 the
United Nations Population Division The United Nations Department of Economic and Social Affairs (UN DESA) is part of the United Nations Secretariat and is responsible for the follow-up to major United Nations Summits and Conferences, as well as services to the United Nations Econo ...
projected that the world's population will reach about 9.8 billion in 2050 and 11.2 billion in 2100. In the future, the world's population is expected to peak, 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. Population has already declined in the last decade or two in Eastern Europe, the Baltics and in the Commonwealth of Independent States. 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. This transition from high birth and death rates to low birth and death rates is often referred to as the
demographic transition 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 (especially of women) and economic development ...
.


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 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 degradationEighty-plus years after the abandonment of Wallaroo Mines (Kadina, South Australia), mosses">Kadina, South Australia">Wallaroo Mines (Kadina, South Australia), mosses remain the only vegetation at some spots of the site's grounds. Environmen ...
, 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 Reproductive rights are legal rights and freedoms relating to reproduction and reproductive health that vary amongst countries around the world. The World Health Organization defines reproductive rights as follows: Reproductive rights rest on th ...
as part of a
human rights Human rights are moral principles or normsJames Nickel, with assistance from Thomas Pogge, M.B.E. Smith, and Leif Wenar, 13 December 2013, Stanford Encyclopedia of PhilosophyHuman Rights Retrieved 14 August 2014 for certain standards of human ...
-based approach. Growing opposition to the narrow population control focus led to a significant change in population control policies in the early 1980s.


See also

*
Community (ecology) In ecology, a community is a group or association of populations of two or more different species occupying the same geographical area at the same time, also known as a biocoenosis, biotic community, biological community, ecological community, ...
*
List of countries by population This is a list of countries and dependencies by population. It includes sovereign states, inhabited dependent territories and, in some cases, constituent countries of sovereign states, with inclusion within the list being primarily based on the I ...
*
Lists of organisms by population This is a collection of lists of organisms by their population. While most of the numbers are estimates, they have been made by the experts in their fields. Species population is a science falling under the purview of population ecology and bioge ...
*
Human overpopulation Humans (''Homo sapiens'') are the most populous and widespread species of primates, characterized by bipedality, opposable thumbs, hairlessness, and intelligence allowing the use of culture, language and tools. They are the only extant members ...
*
Population geography 300px, Map of world population density in 1994 Population Geography relates spatial variations in the distribution, composition, migration, and growth of populations to the terrain. Population geography involves demography in a geographical perspec ...


References


External links


United Nations Population Division


a platform for interaction between research centres and international organizations, such as the United Nations Population Division,
UNFPA The United Nations Population Fund (UNFPA), formerly the United Nations Fund for Population Activities, is a UN agency aimed at improving reproductive and maternal health worldwide. Its work includes developing national healthcare strategies and ...
,
WHO The World Health Organization (WHO) is a specialized agency of the United Nations responsible for international public health. The WHO Constitution, which establishes the agency's governing structure and principles, states its main objective as ...

WHO
and
FAO The Food and Agriculture Organization of the United Nations (FAO)french: Organisation des Nations unies pour l'alimentation et l'agriculture; it, Organizzazione delle Nazioni Unite per l'Alimentazione e l'Agricoltura is a specialized agency of ...
.
Population Reference Bureau
analyzes demographic data and research providing objective, accurate, and up-to-date population information in accessible formats.


NECSP HomePage

Overpopulation

Population World: Population of World
Retrieved 13 February 2004.


United Nations Economic Commission for Europe – Official Web Site

World Population Counter, and separate regions.

WorldPopClock.com
(French)
Populations du monde
(French)
OECD population data

Understanding the World Today
Reports about world and regional population trends * {{Authority control Demography
Countries A country is a distinct territorial body or political entity. It is often referred to as the land of an individual's birth, residence or citizenship. A country may be an independent sovereign state or part of a larger state, as a non-sovereig ...
Population ecology Population models