In biology, a population is all the organisms of the same group or species who live in a particular geographical area and are capable of interbreeding.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.
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).
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.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.
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)and autogamous (self-fertilization) gamodemes.
In ecology, the population of a certain species in a certain area can be estimated using the Lincoln Index.
According to the United States Census Bureau the world's population was about 7.55 billion in 2019and 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.
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,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.
Population growth increased significantly as the Industrial Revolution gathered pace from 1700 onwards.The last 50 years have seen a yet more rapid increase in the rate of population growth due to medical advances and substantial increases in agricultural productivity, particularly beginning in the 1960s, made by the Green Revolution. 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.
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.
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.Growing opposition to the narrow population control focus led to a significant change in population control policies in the early 1980s.
Mendelian inheritance is a type of biological inheritance that follows the principles originally proposed by Gregor Mendel in 1865 and 1866, re-discovered in 1900 and popularised by William Bateson. These principles were initially controversial. When Mendel's theories were integrated with the Boveri–Sutton chromosome theory of inheritance by Thomas Hunt Morgan in 1915, they became the core of classical genetics. Ronald Fisher combined these ideas with the theory of natural selection in his 1930 book The Genetical Theory of Natural Selection, putting evolution onto a mathematical footing and forming the basis for population genetics within the modern evolutionary synthesis.
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 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 services are defined as "educational, comprehensive medical or social activities which enable individuals, including minors, to determine freely the number and spacing of their children and to select the means by which 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, as well as 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 is a branch of population genetics that deals with phenotypes that vary continuously —as opposed to discretely identifiable phenotypes and gene-products.
In population genetics, linkage disequilibrium 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.
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. A lack of fertility is infertility while a lack of fecundity would be called sterility.
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:
"Allogamy" (cross-fertilization) is a term used in the field of biological reproduction describing 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 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.
This article lists current estimates of the world population in history. In summary, estimates for the progression of world population since the late medieval period are in the following ranges:
Population may refer to:
In demographics, the world population is the total number of humans currently living, and was estimated to have reached 7.8 billion people as of March 2020. It took over 200,000 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.
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.
a community of animals, plants, or humans among whose members interbreeding occurs