In 1970, a very clever writer wrote once :
A banal observation has left me stupefied, so much, that I guess that it should have inside an unforgiveness fallacy. I started thinking about the principle that I have two parents, four grandparents, eight great-grandparents and sixteen great-great-grandparents. Why not keep going? Using a pencil and a piece of paper I calculated that progression. In year 1780 I had 64 ancestors (estimating 30 years by generation). In year 1480 I had 65,536 ancestors, in year 1240 I had 16,713,216 ancestors, in year 1060 I had 1,069,645,824. And I didn't go on because it went absurd, in the most historic falsehood. Simply because in year 1060 world population wasn't even up to two thousand million of people. What kind of explanation could have my calculations?