Population is the term typically used to refer to the number of people in a single area. Governments conduct acensus to quantify the size of a resident population within a given jurisdiction. The term is also applied to non-humananimals,microorganisms, andplants, and has specific uses within such fields asecology andgenetics.
Inhumans, interbreeding is unrestricted byracial differences, as all humans belong to the same species of Homo sapiens.
In ecology, the population of a certain species in a certain area can be estimated using theLincoln 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 asdynamical systems. Population dynamics is a branch ofmathematical biology, and uses mathematical techniques such asdifferential equations to model behaviour. Population dynamics is also closely related to other mathematical biology fields such asepidemiology, and also uses techniques from evolutionary game theory in its modelling.
In genetics, apopulation is often defined as a set of organisms in which any pair of members canbreed together. They can thus routinely exchange gametes in order to have usually fertile progeny, and such abreeding 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 appropriatequadratic equation, as shown by SirRonald 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 ofpanmixia 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 appropriatebinomial 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. Inplant andanimal breeding, procedures have been developed which deliberately utilize the effects of dispersion (such as line breeding, pure-line breeding, backcrossing). 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]
According to the UN, the world's population surpassed 8 billion on 15 November 2022,[9] an increase 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 toUNFPA, 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. TheUnited 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 asNigeria 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]
In the future, the world's population is expected to peak at some point,[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.[The date at which it stops growing is the exact same date when it starts to decline.][19][20] Population has already declined in the last decade or two in Eastern Europe, the Baltics and in the former 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 thedemographic transition.[22]
Human population planning is the practice of changing 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 time 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 make people's lives better 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'sreproductive rights as part of ahuman 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]
^"Population". Biology Online. Retrieved5 December 2012.
^"Definition of population (biology)".Oxford Dictionaries. Oxford University Press. Archived fromthe original on 10 May 2013. Retrieved5 December 2012.a community of animals, plants, or humans among whose members interbreeding occurs
CICRED homepage a platform for interaction between research centres and international organizations, such as the United Nations Population Division,UNFPA,WHO andFAO.
Population Reference Bureau analyzes demographic data and research providing objective, accurate, and up-to-date population information in accessible formats.
