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Calculating the answer to the question “How many people have ever lived on Earth?” is complicated. To begin with, when we initially wrote this article back in 1995, “modern” Homo sapiens (that is, people who were roughly like we are now) were thought to have first walked the Earth around 50,000 B.C.E. Discoveries now suggest modern Homo sapiens existed much earlier, around 200,000 B.C.E. This major change in our understanding of human existence spurred new calculations and consultations with experts, resulting in an estimate that about 117 billion members of our species have ever been born on Earth.

How did we reach this number? Dudley Poston Jr., a prominent demographer at Texas A&M University, extended our original analysis to 190,000 B.C.E. and produced an estimate of around 8 billion births between 190,000 B.C.E. and 50,000 B.C.E. Taking Poston’s number into account, we came to our revised estimate of 117 billion people born since 190,000 B.C.E. We also estimate that by 2050 another 4 billion births will increase the number of people who have ever lived on Earth to about 121 billion.

To be sure, calculating the number of people who have ever lived is part science and part art. No demographic data exist for more than 99% of the span of human existence. Still, with some assumptions about population size throughout human history, we can get a rough idea of this number.

What Can We Estimate About Population in Prehistory and History?

Any estimate of the total number of people who have ever lived depends essentially on three factors: the length of time that humans are thought to have been on Earth, the average size of the population at different periods, and the number of births per 1,000 population during each of those periods. The estimate, however, does not depend on the number of deaths during any period of time.

Determining when humankind actually came into existence isn’t straightforward. The oldest hominins are thought to have appeared as early as 7 million B.C.E. The earliest species of the Homo genus appeared around 2 million to 1.5 million B.C.E. Current evidence supports modern Homo sapiens appearing around 190,000 B.C.E. Modern Homo sapiens originated in Africa, though the exact location has long been debated. Diverse groups are thought to have lived in different locations across Africa for the first two-thirds of human history.

Around 8000 B.C.E., the world population was approximately 5 million. (Table 1 displays very rough figures representing averages of an estimate of ranges given by the United Nations and other sources.) Slow population growth over the 8,000-year period—from an estimated 5 million in 8000 B.C.E. to 300 million in 1 C.E.—results in a very low growth rate of only 0.05% per year. It’s difficult to come up with an average world population size for this period. In all likelihood, human populations in different regions grew or declined in response to food availability, the variability of animal herds, periods of peace or hostility, 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. Average life expectancy in Iron Age France (from 800 B.C.E. to about 100 C.E.) has been estimated at only 10 or 12 years. Under these conditions, the birth rate would have to be about 80 live births per 1,000 people just for the species to survive. To put that in perspective, a high birth rate today is about 35 to 45 live births per 1,000 population, and it is observed in only some sub-Saharan African countries.

These short life expectancies mean that the human population had a hard time increasing. One estimate of the population of the Roman Empire, spanning Spain to Asia Minor, in 14 C.E. is 45 million. Other historians, however, set the figure twice as high, suggesting how imprecise population estimates of early historical periods can be.

By 1650, the world’s population rose to about 500 million—not a large increase from the estimate of 300 million in 1 C.E. The average annual rate of growth was actually lower in this period than the rate suggested for 8000 B.C.E. to 1 C.E. One reason for the unusually slower growth was the Black Death. This dreaded plague was not limited to 14th-century Europe but may have begun in western Asia in about 542 C.E. and spread from there. Experts believe that half the Byzantine Empire was destroyed by plague 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, the world population passed the 1 billion mark and has since continued to grow to its current 7.8 billion (our most recent estimate as of 2020). This growth is driven in large part by advances in public health, medicine, and nutrition that have lowered death rates, allowing more people to live far into their reproductive years. 

Assumptions Help Us Estimate Human Population History

Guesstimating the number of people ever born requires determining population sizes for different points in human prehistory and history and applying assumed birth rates to each period. We start at the very, very beginning—with just two people (a minimalist approach!). Although it is unlikely that humans descended from two people, this approach simplifies our estimation.

One complicating factor is the pattern of population growth. Did it rise to some level and then fluctuate wildly in response to famines and changes in climate? Or did it grow at a constant rate? We cannot know the answers to these questions, although paleontologists have produced a variety of theories. For the purposes of this exercise, we assumed a constant growth rate applied to each period up to modern times. Birth rates were set at 80 per 1,000 population annually through 1 C.E. and at 60 per 1,000 from 2 C.E. to 1750. Rates then declined to below the 20s by the modern period (see Table 1).

This semi-scientific approach yields an estimate of about 117 billion births since the dawn of modern humankind. Clearly, the period 190,000 B.C.E. to 1 C.E. is key to our estimate but, unfortunately, little is known about that era’s population size. If we were to challenge our conclusion at all, it might be that our method underestimates the number of births to some degree. The assumption of constant rather than highly fluctuating population growth in the earlier period may underestimate the average population size at the time.

We Account for a Large Percentage of People Who Have Ever Lived

Given a current global population of about 7.8 billion, the revised estimate means that those alive in 2020 represent nearly 7% of the total number of people who have ever lived (see Table 2). Because we have existed on Earth for approximately 200,000 years, that’s actually a fairly large percentage.

TABLE 2. Snapshot of Population History

When we adjusted the date of the first Homo sapiens on Earth from 50,000 B.C.E. to 190,000 B.C.E. our estimate of total humans ever born increased from 109 billion to 117 billion, which is not a large change. But perhaps these two sets of estimates form some sort of boundary as to the possible highs and lows of this slippery issue. As new archaeological discoveries are made and analyzed using increasingly innovative methods, expanding our understanding of human population history, we look forward to yet again tackling this ever-intriguing proposition!

Toshiko Kaneda is a technical director, demographic research at PRB; Carl Haub is a former senior demographer at PRB and is also the author of the original version of this article in 1995.