There is no direct or documentary evidence to know the growth, pattern and density of population of the world during the pre-historic period.
The scholars of population have, however, estimated the population of the past on the basis of circumstantial evidence.
For example, agriculture was unknown before about 8000 B.C.; prior to that all human groups made their living by hunting and gathering.
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Of the earth’s total land area of about 150 million square kilometers, more than 52 million square kilometers could have been successfully utilized in this way by our early ancestors.
From the population densities of hunting and gathering tribes of today, it has been estimated that the total population in 8000 B.C. was about 5 million (Durand, 1973).
They lived in bands of less than fifty people; the men being primarily hunters, whereas the women providing most of the food through plant gathering.
Nowhere on the earth was large population. Typical densities were four persons per 100 square kilometers. There were large uninhabited areas, and each band usually lived in relative isolation from others.
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Such low densities are not surprising because the economies of bands were based on a form of extensive land use. In other words, they obtained their food from large areas without expending much labour per unit of land.
It was the period of high birth and death rates. The high death rates restricted population growth. It is probable that population growth was also restrained by deliberate control through restricted sexual intercourse, abortion, infanticide, and the use of plants having contraceptive competence.
Slow growth for a band meant that its size did not rapidly exceed the carrying capacity of the territory being used for hunting and gathering (Deevey, 1960).
The distribution of population prior to the development of agriculture covered only parts of the old continents.
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By 8000 B.C., hunters and gatherers had migrated from Africa throughout Europe and Asia, to Australia, and across the Bering Straits and southward the length of the America. Only Antarctica was totally uninhabited by mankind.
The size of population at various times from the onset of Agricultural Revolution (8000 B.C.) until the first scanty census data (recorded in the 17th century A.D.) has also been estimated.
It is thought that the total human population at the time of Christ was around 200 to 300 million, and that it has increased to 500 million by 1650 A.D.
In 1850, the world’s population was estimated to be 1,000 million. It means it was doubled from 500 million in 1650 to 1,000 million in 1850. The population doubled again to 2,000 million by 1930. In 1975, it rose to 4,000 million marks and in 1987 became 5,000 million.
The projected population for 2025 and 2050 is about 8 billion and 9 billion respectively. The pattern of human population growth accordingly, not only the size of the population has increased continuously but the rate of increase has also risen stupendously.
According to the estimates, the population, on an average, doubled once after every 1,500 years during the Neolithic period (New Stone Age). The next doubling, from 500 million to 1 billion, took two hundred years and the doubling from 1 billion to 2 billion took only eighty years.
The population reached four billion around 1975, having doubled again in only forty-five years. If the present growth rate of population continues, it will become 7 billion in 2015 to reach 8 billion in 2025 and about 9 billion in 2050.