It's a question I have thought of repeatedly - How many humans have ever lived? This graphic has some real interesting facts and figures on it.
1) How to define "human" - the authors used the figure of 190,000 years, the generally accepted age for Homo sapiens.
2) The human population will hit 8 billion in 2022.
3) This represents about 7% of all people who have ever lived.
4) Including those who are alive today, there have been about 117 billion of us in 190,000 years.