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Demographic history is the reconstructed record of human population in the past. Given the lack of population records prior to the 1950s, there are many gaps in our record of demographic history. Historical demographers must make do with estimates. models and extrapolations. For the methodology, see Historical demography ==Historical population of the world== Estimating the ancestral population of anatomically modern humans, Colin McEvedy and Richard Jones chose bounds based on gorilla and chimpanzee population densities of 1/km² and 3-4/km², respectively, then assumed that as ''Homo erectus'' moved up the food chain, they lost an order of magnitude in density. With a habitat of 68 million km² ("the Old World south of latitude 50° north, minus Australia"), ''Homo erectus'' could have numbered around 1.7 million individuals. After being replaced by ''Homo sapiens'' and moving into the New World and de-glaciated territory, by 10,000 BC world population was approaching four million people. McEvedy and Jones argue that, after populating the maximum available range, this was the limit of our food-gathering ancestors, with further population growth requiring food-producing activities. The initial population "upswing" began around 5000 BC. Global population gained 50% in the 5th millennium BC, and 100% each millennium until 1000 BC, reaching 50 million people. After the beginning of the Iron Age, growth rate reached its peak with a doubling time of 500 years. However, growth slackened between 500 BC and 1 AD, before ceasing around 200 AD. This "primary cycle" was, at this time in history, confined to Europe, North Africa, and mainland Asia. McEvedy and Jones describe a secondary, "medieval cycle" being led by feudal Europe and Song China from around 900 AD. During the period from 500 to 900 AD world population grew slowly but the growth rate accelerated between 900 and 1300 AD when the population doubled. During the 14th century, there was a fall in population associated with the Black Death that spread from Asia to Europe. This was followed by a period of restrained growth for 300 years.〔(Historical Demography ) in Encyclopedia of Public Health, Retrieved on 3 May 2005〕 In the 18th century world population entered a period of accelerated growth. European population reached a peak growth rate of 10 per thousand per year in the second half of the 19th century. During the 20th century, the growth rate among the European populations fell and was overtaken by a rapid acceleration in the growth rate in other continents, which reached 21 per thousand per year in the last 50 years of the millennium. Between 1900 and 2000 CE the population of the world increased by 277%, a fourfold increase from 1.5 billion to 6 billion. The European component increased by 124%, and the remainder by 349%.〔 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「Demographic history」の詳細全文を読む スポンサード リンク
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