Ancestor Paradox

Nobody seems able to solve this riddle, if riddle it is.

As the comment to the linked blog post indicates, inbreeding would not substantially reduce the numbers, at least nowhere near enough to reduce the astonishing mathematical certainty of it all.

I can’t figure this.  Maybe some astute reader can.



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4 responses to “Ancestor Paradox

  1. Min

    “Inbreeding” is the answer, but the term is questionable. Inbreeding is like the royalty of Europe producing idiots.

    For a good answer, ask this anthropologist: Hawks not only knows his stuff, he is a good guy. 🙂


  2. Inbreeding definitely seems like the biggest piece of the puzzle. But the author’s hypothetical assumes that every child comes from one distinct, inclusive couple. This premise assumes no divorce or infidelity.

    He doesn’t account for the situations where one couple divorces and then one or both of those people re-marry and have more children. He doesn’t account for scenarios where the husband or wife pro-create with a third party.

    These situations wouldn’t account for all children, but they would reduce the extent of inbred children.

    Maybe I’m missing something though.


    • I think you’re missing something.

      You’re working back from one existing person, generation by generation. You have two parents and they have to be different people, living at the same time, or at least enough overlap so they had the chance to reproduce together. You have four grandparents and they have to be different people, the same way. People getting divorced or being polygamous way back wouldn’t change the fact that you would still have to have distinct ancestors in each generation.

      So the numbers increase geometrically as you go back. If you postulate lots of inbreeding, you might reduce the ultimate numbers by, say, a third. But that would still leave way too many people 40 generations back, for example.

      It’s a real conundrum, if you ask me.


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