The cumulative human population of planet Earth.

This isn't an assignment, test question or of academic origin in any way.

A question occurred to me a moment ago. How many human beings (Homo sapiens: of genus Homo and species sapiens) have lived, cumulatively? I am uncertain about how to actually go about figuring this out. I imagine it would involve an equation for calculating population growth. The fact that the earliest Homo sapiens found lived around 100,000 years ago would need to be taken in to account. I also imagine with a population equation in hand it would be possible to work from the Earth's current population backwards, cumulatively adding up all the estimated humans. I've tried looking for population equations but I have found a few and am uncertain which would be best to use.

I am eager to see if anyone has any thoughts, or even better, an approximate answer to the question of how many human beings have lived on planet Earth?

P.S. According to Ask.com, the human population of planet earth is 6,446,131,400.

I don't know how they arrived at the estimate, but I read once it was around 600 billion.

You will have to be careful with this one. Adding up humans lived is not the same as adding up life years lived. In other words, if you count 6 billion this year, you can't count these folks next year. You get to count only the new ones. Likewise backwards. Counting people only once is a bit of a trick.

600 billion seems a bit much. I'm thinking this estimate is doing some double counting, maybe 10x counting. I'd expect it to be more like 70 billion.