Tenth cousins, eh?

Someone who is more up with stats and ancestry than I might be able to explain these figures:

Barack Obama and Sarah Palin are 10th cousins through a common ancestor, John Smith, a 17th century pastor, according to genealogists.

I assume that tenth cousin means you share one ancestor 10 generations ago. So is that one of two hundred of those alive at that time?

Yers, of course, I know it takes two to tango, but I\’m not au fait with, haven\’t got at my fingertips, how these statistics work out.

Clearly, we\’re all cousins to some extent, being members of the same species. But narrowing it down to a \”nation\”, \”race\” or region and, well, there\’s some level of cousinry that\’s more likely than not isn\’t there?

I don\’t know and would hope that some one can tell me: what is the average level of cousinry in, say, the UK population? Is there a 50/50 break that we\’re the 10th cousins of some other random Brit? 15th cousin? 25 th cousin?

There must be some such number….it\’ll vary between different places, Icelanders are probably, what, all 6 th cousins? 10th? while Brits are more widely sourced, but does anyone actually know?

5 thoughts on “Tenth cousins, eh?”

  1. I think “Tenth Cousin” should mean a shared ancestor 11 generations back. My kids and my first cousin’s kids would be second cousins, so their genetic paths fully cross at great-grandparents (three generations back).

    I seem to remember an interview with geneticist Steve Jones on (I think) Newsnight some years ago when he said that much of the British population could be as close as fifth cousins, i.e. sharing one set of great-great-great-great grandparents.

    I think.

  2. You’re taking a rather undiverse view of Britishness, I suspect. How does one quantify the relatedness of people from a culture which has pursued first cousin marriage for many generations?

  3. You typically have more great-grandparents (8) than grandparents (4). But you have fewer n-grandparents than m grandparents where n >> m. And you can mix up bloodlines really fast. I recall reading that all it would have taken for everyone in Europe to be related to everyone in Africa was for one Portuguese sailor to have knocked up one girl in Marrakech 500 years ago.

  4. If it is 11 generations back the number of potential parents is 2^10 ie 2048. . The simple number of 2 people so joined will be 2048 x 2048 ie 42 million. This will be reduced by marriages with the family trducing the number of links & increased by families having more than 2 breeding children. All in all this “news” is hardly surprising.

Leave a Reply

Your email address will not be published. Required fields are marked *