Is anybody there? - 27 January 2007 - New Scientist:
From New Scientist Print Edition.
I have two parents, four grandparents, eight great-grandparents, and so on. If I drew a family tree going back 10 generations, I would have to make space for a top line of 1024 ancestors. At 30 generations I would expect to see a line of over a billion ancestors. If I tried to research my family back 40 generations (only about 1000 years) I would be searching for the names of vastly more people than have ever lived. This is impossible, of course, but everyone has two parents, so what exactly is wrong with my reasoning?
The simple answer is that people marry their cousins or half-cousins. If you can have shared ancestors at the close proximity of cousin level, then imagine the number of shared ancestors there would be going back 40 generations." . . .
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From issue 2588 of New Scientist magazine,
27 January 2007, page 97