How many people have ever lived upon earth? There is an urban legend from the 1970s that 75% of the world’s total population from the Year 0 to now is alive today. This, it turns out, is nonsense. Demographer Carl Haub, of the Population Reference Bureau, demolished this factoid a few years ago. His argument is one of the best-read articles on the PRB site, which republished it recently.

Haub stresses that estimating this number is a highly speculative undertaking and requires a number of assumptions. First, when did humanity begin? He assumes that there were 2 of us in the year 50,000BC. By 8,000BC, there were 8 million; by 1AD, 300,000,000; by 1800, 1 billion, and so on up to today’s population of 6.7 billion.

Second, how many people were alive at any one period? Early in our history, the population waxed and waned with famine, disease and natural catastrophes. And third, what was the birth rate? In the Stone Age, the birth rate then was probably double the highest country in the world today. However, the average life expectancy would have been as low as 10 or 12 years because as many as half of the children would have died.

Waving a mathematical wand over his assumptions, Haub comes up with the figure of 106 billion people ever born. “So, our estimate here is that about 5.8 percent of all people ever born are alive today,” he writes. “That's actually a fairly large percentage when you think about it.”