How many people have ever lived?

The global population exploded during the 20th century, aided in part by better public health that reduced infant mortality and increased life expectancy. It now stands at around 7.1 billion. But how many people have lived during the entire time that homo sapiens have been around?

For a long time it was thought that this number was not that much larger than about twice the current population. There can be no definitive answer of course since there is no demographic data for about 99% of that total time period. But recent estimates suggest that the earlier figures were far too low and that the total number is around 108 billion.

Any estimate of the total number of people who have ever been born will depend basically on two factors: the length of time humans are thought to have been on Earth and 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 interesting that the table of estimated figures gives the number of people in 50,000 BCE as just two. I wonder if some will seize on this to suggest that they must be Adam and Eve.