I've never heard most, but I think back the population of earth was only about 6 billion there were people claiming that about 1/5 of people who have ever lived

I've never heard most, but I think back the population of earth was only about 6 billion there were people claiming that about 1/5 of people who have ever lived are alive right now. I've read that at the smallest bottleneck our species had fewer than 10,000 individuals, although I don't think that sad state lasted long.