edit: The reason I find it an odd term is because human ancestry literally doesn’t follow a line. It always branches off, even if only to just include two parents. It’s a tree like structure, a line would misrepresent it

  • bluGill@fedia.io
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    5 hours ago

    A tree is a terrible representation since people will appear in more than one place on it. brother sisters marriages (which did happen) tend to produce deformed kids, but first cousins have good odds for normal kids. By third cousin odds of genetic issues was close enough to zero, but those kids will have six great great grand parents not the mathematical eight. I didn’t mention half siblings but that happens too and a couple generations below could marry safely.

    the above isn’t just theoretical. Before modern transport you often lived and married in the same village for many generations. It would often be impossible to find anyone to have kids with that wasn’t at least sixth cousins from more than one path.