Posted elsewhere but would like explained like I’m 5.
What I can’t get my head around is: I had 2 parents, they had 4 (in total) who would have had 8 in a geometric progression, so going back even 1000 years or 20 generations (assuming an average lifespan of 50 years) is 2,097,152 ancestors for just me, and given that there is a reported 7.9 billion people on earth alive today it seems mathematically impossible that all those people could have existed.
In: 7
If you marry your first cousin, then your child has six great-grandparents, not eight, because two are duplicates. Expand as necessary.
> Demographer Kenneth Wachtel estimates that the typical English child born in 1947 would have had around 60,000 theoretical ancestors at the time of the discovery of America. Of this number, 95 percent would have been different individuals and 5 percent duplicates. […] At the time of the Black Death, he’d have had 3.5 million — 30 percent real, 70 percent duplicates. The maximum number of “real” ancestors occurs around 1200 AD — 2 million, some 80 percent of the population of England.
https://www.straightdope.com/21341588/2-4-8-16-how-can-you-always-have-more-ancestors-as-you-go-back-in-time
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