How many people have ever lived on earth?

blog.world-mysteries.com

The above estimate shows  that about 5.8 percent of all people ever born are alive today.  That’s actually a fairly large percentage when you think about it. Source: Population Reference Bureau estimates.

The number is difficult to estimate for the following reasons:
* The set of specific characteristics that define a human is a matter of definition, and it is open to debate which members of early Homo sapiens and earlier or related species of Homo to include. See in this regard also Sorites paradox. Even if the scientific community reached wide consensus regarding which characteristics distinguished human beings, it would be nearly impossible to pinpoint the time of their first appearance to even the nearest millennium because the fossil record is simply too sparse. However, the limited size of population in early times compared to its recent size makes this source of uncertainty of limited importance.
* Robust statistical 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 Ancient Egypt and in the Persian Empire the focus was on counting merely a subset of the people for purposes of taxation or military service.[108] All claims of population sizes preceding the 18th century are estimates, and thus the margin of error for the total number of humans who have ever lived should be in the billions, or even tens of billions of people.
* A critical item for the estimation is life expectancy. Using a figure of twenty years and the population estimates above, one can compute about fifty-eight billion. Using a figure of forty yields half of that. Life expectancy varies greatly when taking into account children who died within the first year of birth, a number very difficult to estimate for earlier times. Haub states that “life expectancy at birth probably averaged only about ten years for most of human history”[106] His estimates for infant mortality suggest that around 40% of those who have ever lived did not survive beyond one year. [ Source: http://en.wikipedia.org/wiki/World_population ]
Estimated world population at various dates (in millions)Source: http://en.wikipedia.org/wiki/World_population