Population

The term is also applied to non-human animals, microorganisms, and plants, and has specific uses within such fields as ecology and genetics.

[citation needed] In ecology, a population is a group of organisms of the same species which inhabit the same geographical area and are capable of interbreeding.

[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.

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.

According to a separate estimate by the United Nations, Earth's population exceeded seven billion in October 2011.

[10] According to papers published by the United States Census Bureau, the world population hit 6.5 billion on 24 February 2006.

The population of countries such as Nigeria 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.

[17] 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.

[21] The population pattern of less-developed regions of the world in recent years has been marked by gradually declining birth rates.