It's an Anomaly You are Even Here.Fascinating, Horrifying: "Life expectancy at birth probably averaged only about 10 years for most of human history."

Prehistory and History
Any estimate of the total number of people who have ever been born will depend basically on two factors: (1) the length of time humans are thought to have been on Earth and (2) the average size of the human population at different periods.

Fixing a time when the human race actually came into existence is not a straightforward matter. Various ancestors of Homo sapiens seem to have appeared at least as early as 700,000 B.C. Hominids walked the Earth as early as several million years ago. According to the United Nations' Determinants and Consequences of Population Trends, modern Homo sapiens may have appeared about 50,000 B.C. This long period of 50,000 years holds the key to the question of how many people have ever been born.

At the dawn of agriculture, about 8000 B.C., the population of the world was somewhere on the order of 5 million. (Very rough figures are given in the table; these are averages of an estimate of ranges given by the United Nations and other sources.) The slow growth of population over the 8,000-year period, from an estimated 5 million to 300 million in 1 A.D., results in a very low growth rate — only 0.0512 percent per year. It is difficult to come up with an average world population size over this period. In all likelihood, human populations in different regions grew or declined in response to famines, the vagaries of animal herds, hostilities, and changing weather and climatic conditions.

In any case, life was short. Life expectancy at birth probably averaged only about 10 years for most of human history. Estimates of average life expectancy in Iron Age France have been put at only 10 or 12 years. Under these conditions, the birth rate would have to be about 80 per 1,000 people just for the species to survive. Today, a high birth rate would be about 45 to 50 per 1,000 population, observed in only a few countries of Africa and in several Middle Eastern states that have young populations.

Our birth rate assumption will greatly affect the estimate of the number of people ever born. Infant mortality in the human race's earliest days is thought to have been very high — perhaps 500 infant deaths per 1,000 births, or even higher. Children were probably an economic liability among hunter-gatherer societies, a fact that is likely to have led to the practice of infanticide. Under these circumstances, a disproportionately large number of births would be required to maintain population growth, and that would raise our estimated number of the "ever born."

By 1 A.D., the world may have held about 300 million people. One estimate of the population of the Roman Empire, from Spain to Asia Minor, in 14 A.D., is 45 million. However, other historians set the figure twice as high, suggesting how imprecise population estimates of early historical periods can be.

By 1650, world population rose to about 500 million, not a large increase over the 1 A.D. estimate. The average annual rate of growth was actually lower from 1 A.D. to 1650 than the rate suggested above for the 8000 B.C. to 1 A.D. period. One reason for this abnormally slow growth was the Black Death. This dreaded scourge was not limited to 14th-century Europe. The epidemic may have begun about 542 A.D. in western Asia, spreading from there. It is believed that half the Byzantine Empire was destroyed in the sixth century, a total of 100 million deaths. Such large fluctuations in population size over long periods greatly compound the difficulty of estimating the number of people who have ever lived.

By 1800, however, world population had passed the 1 billion mark, and it has continued to grow since then to the current 6 billion.

Guesstimates
Guesstimating the number of people ever born, then, requires selecting population sizes for different points from antiquity to the present and applying assumed birth rates to each period (see table). We start at the very, very beginning — with just two people (a minimalist approach!).


-------------------------------------------------------------​-------------------

How Many People Have Ever Lived On Earth?

Year Population Births per 1,000 Births Between Benchmarks
50,000 B.C. 2 - -
8000 B.C. 5,000,000 80 1,137,789,769
1 A.D. 300,000,000 80 46,025,332,354
1200 450,000,000 60 26,591,343,000
1650 500,000,000 60 12,782,002,453
1750 795,000,000 50 3,171,931,513
1850 1,265,000,000 40 4,046,240,009
1900 1,656,000,000 40 2,900,237,856
1950 2,516,000,000 31-38 3,390,198,215
1995 5,760,000,000 31 5,427,305,000
2002 6,215,000,000 23 983,987,500

Number who have ever been born 106,456,367,669
World population in mid-2002 6,215,000,000
Percent of those ever born who are living in 2002 5.8


Source: Population Reference Bureau