It is estimated that about 100 billion human beings have ever lived on Earth.
Why it is true
This means that for every person alive today, there are roughly 15 people who have died in all of human history, showing how vast our ancestral lineage truly is.
Source: Demographics
Would you rather be asked first?
This is the reading side of the site, so the answer is in the sentence above — that is the whole point of it. Test yourself works the other way round: the question comes on its own, and the fact and the explanation only appear once you have answered.