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
Most people would be surprised to find that they probably don’t have to go very far back in their lineage before ancestors start to “overlap” (to put it nicely)
Travel wasn’t really any significant part of people’s lives until the last century or so. Most of human history, people didn’t go very far and only interacted with relatively small populations. Most people in these smaller areas were somewhat related.
Not to mention, your ancestor count would actually shrink at critical mutation points. For example, all of your ancestors would converge at mitochondrial eve, then again at Y chromosomal Adam, etc.
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