For other uses see Population (disambiguation).
In biology, a population is the collection of inter-breeding organisms of a particular species; in sociology, a collection of human beings. Individuals within a population share a particular characteristic of interest, most often that of living in a given geographic area. In addition, on average, populations often show differences in morphological, physiological, life history or behavioral characteristics. In taxonomy, population is a low-level taxonomic rank.
Human populations can be defined by any characteristics such as mortality, migration, family (marriage and divorce), public health, work and the labor force, and family planning. Various aspects of human behavior in populations are also studied in sociology, economics, and geography.
Study of populations is almost always governed by the laws of probability, and the conclusions of the studies may thus not always be applicable to some individuals. This odd factor may be reduced by statistical means, but such a generalization may be too vague to imply anything. Demography is used extensively in marketing, which relates to economic units, such as retailers, to potential customers. For example, a coffee shop that wants to sell to a younger audience looks at the demographics of an area to be able to appeal to this younger audience.
See main article: World population. According to papers published by the United States Census Bureau, the world population hit 6.5 billion (6,500,000,000) on February 25, 2006. The United Nations Population Fund designated October 12, 1999 as the approximate day on which world population reached 6 billion. This was about 12 years after world population reached 5 billion in 1987, and 6 years after world population reached 5.5 billion in 1993. However, the population of some countries, such as Nigeria, is not even known to the nearest million, so there is a considerable margin of error in such estimates.
In 2007 the United Nations Population Division projected that the world's population will likely surpass 10 billion in 2055. The last 50 years have seen a rapid increase in population due to medical advances and substantial increase in agricultural productivity, particularly in the period 1960 to 1995 made by the Green Revolution.
In the future, world population has been expected to reach a peak of growth, from there it will decline due to economic reasons, health concerns, land exhaustion and environmental hazards. There is around an 85% chance that the world's population will stop growing before the end of the century. There is a 60% probability that the world's population will not exceed 10 billion people before 2100, and around a 15% probability that the world's population at the end of the century will be lower than it is today. For different regions, the date and size of the peak population will vary considerably.