Generations, pedigree collapse and mind-blowing stuff

Here’s something that’s quite obvious when you think about it, but perhaps you’ve never had much reason to do so.  We each have:

  • 4 x grandparents
  • 8 x G grandparents
  • 16 x 2G grandparents
  • 32 x 3G grandparents
  • 64 x 4G grandparents
  • 128 x 5G grandparents
  • 256 x 6G grandparents
  • 512 x 7G grandparents
  • 1024 x 8G grandparents
  • 2048 x 9G grandparents
  • 4096 x 10G grandparents

In other words, the number of grandparents doubles with every generation.

Since the earliest parish records start at 1538 (and most of them later than that), unless you have aristocratic lineage, you won’t be able to get back much further than 10xG grandparents.  But look how many there are for you to find!  Surely a lifetime’s dedicated work to track down the 8190 direct ancestors across all generations from you to your 10xG grandparents.  That puts our results into perspective doesn’t it!

But there’s another important point to come out of all this: something referred to as pedigree collapse:

Continuing the doubling up of direct ancestors and going back just a few more generations, we each have 4,194,304 x 20G grandparents and 67,108,864 x 25G grandparents; and after that my calculator runs out of spaces for the required numbers, but people with better calculators (or brains!) have worked out that after thirty generations, which brings us to the Middle Ages, we each have roughly a billion ancestors – an impossibly high figure because this is greater than the total world population at that time.  (See the Wikipedia entry on Pedigree Collapse here.)

The only explanation is that some of our ancestors are related to each other.  Sometimes this is quite obvious.  For example, a marriage between cousins (which has always been permissible in the UK) means their offspring will have six rather than the usual eight G grandparents, and therefore 12 GG grandparents, 24 GGG grandparents, and so on…

But what about less obvious connections?  I’ve found that a member of my family and his wife (and me!) are descended from the same 9xG grandparents, making them 10th cousins.  I’m also on the hunt for a connection between my paternal grandparents who seem to be related at around 8th cousin or earlier, their ancestors having moved off in different directions before reuniting in Leeds in the 20th century.  I’ll probably never know their most recent common ancestors, since their connection may be just before records began, but I know the surname and I know whereabouts they lived.  And although I love this idea and will never cease to be delighted at finding such connections, bearing in mind all of the above it seems this is to be expected rather than the wonderful coincidence it seems to be.

It’s even suggested that every single one of us is related to every other person on Earth as 50th cousin or closer.  Go back far enough and we are all family!

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