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
There’s a lot of inbreeding, people marrying nth cousins.
An extreme example: It’s estimated that the 12 million Ashkenazi Jews alive today are descended from apx. 350 individuals who lived around 1350 A.D. with < 0.5% outside DNA per generation. All of them are no more distant than 6th cousins.
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