Earth will soon be home to seven billion humans. If you find that hard to fathom, try grasping how many have ever walked the planet. That’s what American demographer Carl Haub wanted to find out when, in 1975, he heard someone say that 75 percent of the people who’d ever been born were alive at that time. Dubious, he set out to disprove it, taking two main things into account:
(1) the assumed dawn of humanity and
(2) average populations at different periods of time.
Using 50,000 B.C. as his starting point, Haub applied crude birthrates—the number of annual births per thousand people—to each population set, then added them.
His estimate? In 1975, 103 billion people had lived, but only 4 percent of them were alive at that time.
Applied to 2011, says Haub, those numbers are 108 billion, and 6.4 percent.
—Extract from a National Geographic item by Catherine Zuckerman.
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