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
It’s almost like we’re all related and should treat strangers as though they are part of an extended family. 🤔
Ancestor lines collapse in case of close cousins having children. My great grandfather married his cousin, so they had many of the same ancestors.
Suppose each person has 2 million ancestors (at generation 20). And there are 8 billion people on earth.
Multiply these two together, and you get 16 quadrillion, You’re right, there were not that many people alive back then. But that’s the wrong way to count the total, because you’ve gone and double-counted a lot of ancestors.
Your brothers and sisters, for example, all share the same 2 million ancestors. Even if you’re an only child, many people are not. Also, you share a lot of ancestors with your cousins, second cousins, etc.
We’re all distantly related, in fact, and often not as distantly as you might think.
Also because of this, some of your “2 million ancestors” are the same person. For example, maybe your father’s father’s mother’s father’s mother’s father and your mother’s father’s father’s mother’s mother’s father’s father are actually the same person. So you don’t actually have 2 million 20th generation ancestors, you’ve double-counted a lot of them as well.
You are more closely related to strangers on the street than you think. Those 2’097’152 ancestors aren’t just your ancestors. They are likely the same ancestors for most people in your country, if not even the whole planet.
Think of it like this: You have 1 kid. Your kid has 1 kid. Your grand kid has 1 kid. Your great grandchild is now related not just to you, but to your wife, your kids wife (and all her ancestors), your grand kids wife (and all her ancestors). And this isn’t even including siblings.
Theres a good chance you and I share the same ancestors if you go back just 10 generations.
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