how many people have ever lived?

That is exactly the question that occurred to me the other day, for reasons which will remain unexplained. Turns out the internet has a few answers. At least one of them uses the same methodology a friend of mine had come up with (with some more accurate numbers). By both official-looking estimates I saw, there have been about 100 billion human births in the past five hundred to one million years (yes, the number does not change a lot if you double the time span). That puts the current world population at about 6% of the total.

Here's a link to a pretty official-looking article, which uses UN numbers. For the more mathematically inclined, here is a page about how a guy named Keyfitz went about calculating the number.