Population

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The distribution of world population in 1994 Population density.png
The distribution of world population in 1994
Key Population density key.png
Key

In biology, a population is a number of all the organisms of the same group or species who live in a particular geographical area and are capable of interbreeding. [1] [2] 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. [3]

Contents

In sociology, population refers to a collection of humans. Demography is a social science 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 a sexual population is a set of organisms in which any pair of members can 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. [4] 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. [5]

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). 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 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) [6] and autogamous (self-fertilization) gamodemes. [7]

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

World human population

According to the United States Census Bureau the world's population was about 7.55 billion in 2019 [8] 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. [9]

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, [10] so there is a considerable margin of error in such estimates. [11]

Researcher Carl Haub calculated that a total of over 100 billion people have probably been born in the last 2000 years. [12]

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. [13] The last 50 years have seen a yet more rapid increase in the rate of population growth [13] due to medical advances and substantial increases in agricultural productivity, particularly beginning in the 1960s, [14] made by the Green Revolution. [15] 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. [16]

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, [17] 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. [18] [19] Population has already declined in the last decade or two in Eastern Europe, the Baltics and in the Commonwealth of Independent States. [20]

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. [21] This transition from high birth and death rates to low birth and death rates is often referred to as the demographic transition. [21]

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 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. [22] Growing opposition to the narrow population control focus led to a significant change in population control policies in the early 1980s. [23]

See also

Related Research Articles

Reproduction 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 "parents". Reproduction is a fundamental feature of all known life; each individual organism exists as the result of reproduction. There are two forms of reproduction: asexual and sexual.

Inbreeding Production of offspring from the mating of individuals of a population who are more closely related than the average members of the population.

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 or recessive traits resulting from incestuous sexual relationships and consanguinity.

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.

Ex situ conservation literally means, "off-site conservation". It is the process of protecting an endangered species, variety or breed, of plant or animal outside its natural habitat; for example, by removing part of the population from a threatened habitat and placing it in a new location, which may be a wild area or within the care of humans. The degree to which humans control or modify the natural dynamics of the managed population varies widely, and this may include alteration of living environments, reproductive patterns, access to resources, and protection from predation and mortality. Ex situ management can occur within or outside a species' natural geographic range. Individuals maintained ex situ exist outside an ecological niche. This means that they are not under the same selection pressures as wild populations, and they may undergo artificial selection if maintained ex situ for multiple generations.

Family planning Planning of when to have children, and the use of birth control and other techniques to implement such plans

Family planning services are "educational, comprehensive medical or social activities which enable individuals, including minors, to determine the number and spacing of their children freely and to select how this may be achieved." Family planning may involve consideration of the number of children a woman wishes to have, including the choice to have no children and the age at which she wishes to have them. These matters are influenced by external factors such as marital situation, career considerations, financial position, and any disabilities that may affect their ability to have children and raise them. 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.

Quantitative genetics The study of the inheritance of continuously variable traits

Quantitative genetics deals with phenotypes that vary continuously —as opposed to discretely identifiable phenotypes and gene-products.

Human variability, or human variation, is the range of possible values for any characteristic, physical or mental, of human beings.

In population genetics, linkage disequilibrium (LD) is the non-random association of alleles at different loci in a given population. Loci are said to be in linkage disequilibrium when the frequency of association of their different alleles is higher or lower than what would be expected if the loci were independent and associated randomly.

Balancing selection refers to a number of selective processes by which multiple alleles are actively maintained in the gene pool of a population at frequencies larger than expected from genetic drift alone. This can happen by various mechanisms, in particular, when the heterozygotes for the alleles under consideration have a higher fitness than the homozygote. In this way genetic polymorphism is conserved.

The effective population size is the number of individuals that an idealised population would need to have in order for some specified quantity of interest to be the same in the idealised population as in the real population. Idealised populations are based on unrealistic but convenient simplifications such as random mating, simultaneous birth of each new generation, constant population size, and equal numbers of children per parent. In some simple scenarios, the effective population size is the number of breeding individuals in the population. However, for most quantities of interest and most real populations, the census population size N of a real population is usually larger than the effective population size Ne. The same population may have multiple effective population sizes, for different properties of interest, including for different genetic loci.

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

Inbreeding depression is the reduced biological fitness in a given population as a result of inbreeding, or breeding of related individuals. Population biological fitness refers to an organism's ability to survive and perpetuate its genetic material. Inbreeding depression is often the result of a population bottleneck. In general, the higher the genetic variation or gene pool within a breeding population, the less likely it is to suffer from inbreeding depression.

Allogamy or cross-fertilization is the fertilization of an ovum from one individual with the spermatozoa of another. By contrast, autogamy is the term used for self-fertilization. In humans, the fertilization event is an instance of allogamy. Self-fertilization occurs in hermaphroditic organisms where the two gametes fused in fertilization come from the same individual. This is common in plants and certain protozoans.

World Population Day

World Population Day is an annual event, observed on July 11 every year, which seeks to raise awareness of global population issues. The event was established by the Governing Council of the United Nations Development Programme in 1989. It was inspired by the public interest in Five Billion Day on July 11, 1987, the approximate date on which the world's population reached five billion people. World Population Day aims to increase people's awareness on various population issues such as the importance of family planning, gender equality, poverty, maternal health and human rights.

Selfing or self-fertilization is the union of male and female gametes and/or nuclei from same haploid, diploid, or polyploid organism. It is an extreme degree of inbreeding.

Population may refer to:

World population Total number of living humans on Earth

In demographics, the world population is the total number of humans currently living, and was estimated to have reached 7,800,000,000 people as of March 2020. It took over 2 million years of human history for the world's population to reach 1 billion, and only 200 years more to reach 7 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.

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.

References

  1. "Population". Biology Online. Retrieved 5 December 2012.
  2. "Definition of population (biology)". Oxford Dictionaries. Oxford University Press. Retrieved 5 December 2012. a community of animals, plants, or humans among whose members interbreeding occurs
  3. Hartl, Daniel (2007). Principles of Population Genetics. Sinauer Associates. p. 45. ISBN   978-0-87893-308-2.
  4. Hartl, Daniel (2007). Principles of Population Genetics. Sinauer Associates. p. 95. ISBN   978-0-87893-308-2.
  5. Fisher, R. A. (1999). The Genetical Theory of Natural Selection. Oxford University Press. ISBN   978-0-19-850440-5.
  6. 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.
  7. 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.
  8. "Population Clock". www.census.gov. Retrieved 29 January 2019.
  9. to a World of Seven Billion People Archived 13 January 2012 at the Wayback Machine UNFPA 12 September 2011
  10. "Cities in Nigeria: 2005 Population Estimates – MongaBay.com" . Retrieved 1 July 2008.
  11. "Country Profile: Nigeria". BBC News. 24 December 2009. Retrieved 1 July 2008.
  12. Haub, C. 1995/2004. "How Many People Have Ever Lived on Earth?" Population Today, "Archived copy". Archived from the original on 24 April 2013. Retrieved 29 April 2013.CS1 maint: archived copy as title (link)
  13. 1 2 As graphically illustrated by population since 10,000BC and population since 1000AD
  14. "The end of India's green revolution?". BBC News. 29 May 2006. Retrieved 29 November 2009.
  15. Food First/Institute for Food and Development Policy Archived 14 July 2009 at the Wayback Machine
  16. "UN Population Prospects 2017" (PDF).
  17. World Population Development Statistics: Forecast, United Nations, 2011.
  18. Lutz, Wolfgang; Sanderson, Warren; Scherbov, Sergei (2001). "The End of World Population Growth" (PDF). Nature. 412 (6846): 543–545. doi:10.1038/35087589. PMID   11484054.
  19. 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 .
  20. "world demographic trends". gsociology.icaap.org. Retrieved 18 July 2019.
  21. 1 2 "Archived copy". Archived from the original on 30 March 2009. Retrieved 7 April 2009.CS1 maint: archived copy as title (link)
  22. Knudsen, Lara (2006). Reproductive Rights in a Global Context . Vanderbilt University Press. pp.  2. ISBN   978-0-8265-1528-5. reproductive rights.
  23. Knudsen, Lara (2006). Reproductive Rights in a Global Context . Vanderbilt University Press. pp.  4–5. ISBN   978-0-8265-1528-5. reproductive rights.