What is the total number of humans that have ever walked the earth?

Question

What is the total number of humans that have ever walked the earth? Estimated

Answer 1

In the introduction to his 1968 science fiction novel "2001: A Space Odyssey", the noted author Arthur C. Clarke wrote:

"Since the dawn of time, roughly a hundred billion human beings have walked the planet Earth."

Clarke is an expert scientist, not just a novelist, and he would have based his figure on the best data and most reasonable assumptions that he could. The Wikipedia page on the subject offers a much wider range of estimates, but while not actually mentioning Clarke, agrees with him by saying that "many of the more robust estimates fall into the range of 90 to 110 billion".

Answer 2

This is a very good question, and has been the source of some argument. The current theory is that a lot more people have died than are now alive, and estimates of the total number vary from between 45 to 100 billion.
Here is a reference to the wikipedia page on world population, which contains a paragraph on the total number of people who have ever lived:
http://en.wikipedia.org/wiki/World_population#Number_of_humans_that_have_ever_lived

Answer 3

I don't know the answer for a fact, but I recall being told some 30 years ago or so that there were more people alive at the time than had lived up until that time. I never did a calculation to verify this. In the intervening 30 years, there have been a couple billion more people added to the earth, so I would guess that somewhere around 10 to 12 billion would be about right.

Edit. I learned something today too, so you get a star.