It seems an impossible question to answer. How many people have ever lived on planet Earth?
It's more than just a matter of curiosity. Demographers use historical data to project future population trends, such as when global population growth is expected to peak. Governments use this data to plan for future infrastructure, healthcare, education, and food supply needs. The information is also very useful for resource management.
Calculating the number of humans who have ever lived requires a starting point. Here's where our first argument among scientists occurs. When did modern homo sapiens arise? Since there was no writing to tell us, all we have is the fossil record. That tells us that the first modern humans rose in several different places in Africa around 300,000 years ago. The Population Reference Bureau (PRB) chose 190,000 BC, close to the accepted estimate (200,000 BC) for the emergence of anatomically modern humans, as a starting point.
From then until today, PRB estimates that 117 billion human beings have drawn breath. "It is a number with the crispness of arithmetic and the uncertainty of archaeology," writes Tibi Puiu of ZME Science. "No census taker stood in Ice Age Africa. No state authority counted the births of Paleolithic foragers."
The PRB researchers estimated how many people were alive at different points in history (the Persian Empire, the Greeks, the Romans), then estimated how many babies were born per 1,000 people and added the babies born between each benchmark.
There's a lot of wiggle room in all those numbers, especially from prehistory. PBR dealt with facts like how many Neolithic human campsites were found in Africa, dated more than 100,000 years ago.
How many people were alive in the Roman Empire's heyday? Around 14 BC, PBR estimates that about 45 million people were alive. Some historians have suggested roughly twice that. If so much disagreement occurs over one relatively well-studied empire, the problems faced by PBR scientists and historians become clearer.
The PRB estimate assumes about 5 million people in 8000 BCE, 300 million in 1 CE, 500 million by 1650, and roughly 1 billion around 1800. Then the line bends sharply upward, which coincides with major advances in science that improved living standards, raised life expectancy, and drastically reduced childhood mortality. The world reached 2 billion in 1927, 4 billion in 1974, and 8 billion in 2022.
Add everything up, and you get 117,020,448,575 people ever born by 2022.
Simple? Not hardly. But consider that for almost the entirety of human history, birth rates had to be astronomically high just to keep humanity from going extinct.
PBR notes "that life expectancy at birth may have averaged only about 10 years for much of human history, not because most people dropped dead at 10, but because so many children died very young," writes Puiu. "In Iron Age France, life expectancy has been estimated at only 10 or 12 years.
"In those conditions, the birth rate may have needed to reach about 80 live births per 1,000 people per year," Puiu says. Compared to the birth rate today in Somalia, which is 40 to 43 live births per 1,000 women, 80 births per 1,000 tells a vivid story of human survival in pre-history. This is why population growth for so much of our history was so slow. "Humans were born in large numbers, but disease, hunger, childbirth, violence, and childhood mortality carried many away," writes Puiu. "For thousands of generations, humanity ran hard merely to stay in place."
Plague and famine made the pattern even more uneven. By 1650, the world population was only about 500 million, a modest rise from the estimate of 300 million in 1 CE. The Black Death and earlier plague waves inflicted enormous losses.
Human populations spiked in waves, beginning with the advent of agriculture. But the modern population explosion required public health, sanitation, better nutrition, vaccination, safer childbirth, antibiotics, pasteurised milk, and medicine. These did not make humans more fertile. They made death less certain.
By the 1850s, reaching the age of 65 was rare. Half of all people who have ever reached age 65 may be alive today, according to The Economist.
There is a lot of disagreement over the "117 billion humans who have ever lived" number. Given infant mortality in the earliest human families and until the 20th century, some scientists think that a more realistic number is twice that.
Whatever the actual number, the exercise in searching for it taught us as much about ourselves as it did the struggles of past humans to survive.
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