thumb|350px|Distribution of world population in 1994.

World population

main: 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 24, 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. Population growth increased significantly as the Industrial Revolution gathered pace from 1700 onwardsAs graphically illustrated by population since 10,000BC and population since 1000AD. 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 in the period 1960 to 1995 made by the Green Revolution. In 2007 the United Nations Population Division projected that the world's population will likely surpass 10 billion in 2055. 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.

Population control

main: Population control Population control is the practice of curtailing population increase, usually by reducing the birth rate. Surviving records from Ancient Greece document the first known examples of population control. These include the colonization movement, which saw Greek outposts being built across the Mediterranean and Black Sea basins to accommodate the excess population of individual states. Infanticide, including abortion, was encouraged in some Greek city states in order to keep population down.

An important example of mandated population control is People's Republic of China's one-child policy, in which having more than one child is made extremely unattractive. This has led to allegations that practices like forced abortions, forced sterilization, and infanticide are used as a result of the policy. The country's sex ratio at birth of 114 boys to 100 girls may be evidence that the latter is often sex-selective. However, other countries without a one-child policy also have similar sex ratios but for different reasons such as nutritionFact: date=July 2008.