How Many People Have Ever Lived on Earth?

Given that there are about 7 billion people at the moment, my answer to this question was about 15 billion. Here I was thinking about exponential growth, but I was way off. The estimated value is just over 100 billion. The article sets out to debunk something of a myth in population studies

One reason the question keeps coming up is that somewhere, at some time back in the 1970s, a now-forgotten writer made the statement that 75 percent of the people who had ever been born were alive at that moment.