The first is only hundreds of thousands, starting with anatomically modern humans and not all of our precursors who lived for millions of years before that.
Though that may not change much -- depending on your estimates, Neanderthals probably spanned 3-30 billion person-years, as little as 0.1% of modern humans. All human precursors (5-10My worth) might be margin of error on the modern humans' totals.
On the other end of things, if we plateau at around 10 billion humans, it will only take about 75 years to accumulate the next third (well, quarter) of human existence.
Though that may not change much -- depending on your estimates, Neanderthals probably spanned 3-30 billion person-years, as little as 0.1% of modern humans. All human precursors (5-10My worth) might be margin of error on the modern humans' totals.
On the other end of things, if we plateau at around 10 billion humans, it will only take about 75 years to accumulate the next third (well, quarter) of human existence.