A POPULATION is all the organisms of the same group or species , which live in a particular geographical area , and have the capability of interbreeding.
The area that is used to define a sexual population is defined as the area where inter-breeding is potentially possible between any pair within the area, and where the probability of interbreeding is greater than the probability of cross-breeding with individuals from other areas.
In sociology , population refers to a collection of humans .
* 1 Population genetics (ecology)
* 2 World human population
* 2.1 Predicted growth and decline * 2.2 Control
* 3 See also * 4 References * 5 External links
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 _Gamo deme_. This also implies that all members belong to the same species. If the Gamo deme is very large (theoretically, approaching infinity), and all gene alleles are uniformly distributed by the gametes within it, the Gamo deme 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 Gamo demes which exchange gametes reasonably uniformly within themselves but are virtually separated from their neighboring Gamo demes. 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 Gamo demos 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 Gamo demes. 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 Gamo demes 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) Gamo demes.
In ecology, the population of a certain species in a certain area can be estimated using the Lincoln Index .
WORLD HUMAN POPULATION
As of today's date, the world's population is estimated by the United
States Census Bureau to be 7.524 billion . The US Census Bureau
estimates 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 papers published by the United States Census Bureau, the
world population hit 6.5 billion on 24 February 2006. The United
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
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). Main article:
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.
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 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.
* ^ "Population". Biology Online. Retrieved 5 December 2012.
* ^ "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
* ^ Hartl, Daniel (2007). _Principles of