Human Demography and the Power of 2^n

Jason Kuznicki asks a question:

I Learned It on Wikipedia:

Using mathematical models, it is easy to demonstrate that every human being alive today is likely to be a direct descendant of Confucius, even using mathematical models that assume an extremely small amount of cross cultural mating, since any human alive today would have had 1.5 sextillion ancestors alive at the time of Confucius, over a quadrillion times more than the population of the earth at the time, making...