"How many people have every walked on 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...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."
From National Geographic; June 2011
http://hanovergraphics.tumblr.com/
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