The Puzzler

What percentage of people who have ever lived are alive today?

Over at the 1000 Memories blog, Jonathan Good poses that question and does some math to come to a reasonable answer.

Estimates suggest that it took 190,000 years for the population to reach 4 million (in a modern context that’s the number of people who ride the NYC subway each morning!). It wasn’t until the dawn of the industrial era in 1800 that our global population hit a seventh of what it is now, inching towards 1 billion. It’s rocketed ever since.

Before you click over, take a stab at a guess. The actual answer seems high to me, but then I asked a few people, and they all guess way higher. Seems like this is one of those questions that is completely without context, so any of a range of numbers could be plausible.