Estimates of the total number of humans who have ever lived range in the order of
100 billion. Estimates of this kind cannot hope to give more than the rough order of magnitude, as even modern population estimates are fraught with uncertainties of the order of 3% to 5%.
[163] Kapitzka (1996) cites estimates ranging between 80 and 150 billion.
[164]Another such estimate was prepared by Haub (1995), updated in 2002 and 2011; the 2011 figure was approximately 107 billion.
[22][23][165] Haub characterized this figure as an estimate that required "selecting population sizes for different points from antiquity to the present and applying assumed birth rates to each period".
[23]
The very small size of the world population in prehistoric times (as compared to its current size) facilitates this kind of estimate with regard to the
semantic difficulty of deciding the precise meaning of "human" (in the context
early Homo sapiens). More importantly, robust population data only exist for the last two or three centuries. Until the late 18th century, few governments had ever performed an accurate census. In many early attempts, such as in
Ancient Egypt and the
Persian Empire, the focus was on counting merely a subset of the population for purposes of taxation or military service.
[166] Thus, there is a significant margin of error when estimating ancient global populations.
Another critical factor for such an estimate is the question of pre-modern
infant mortality rates; these figures are very difficult to estimate for ancient times due to a lack of accurate records. Haub (1995) estimates that around 40% of those who have ever lived did not survive beyond their first birthday. Haub also stated that "
life expectancy at birth probably averaged only about ten years for most of human history".
[23]
