"But when we get to 40 generations ago, in the time of Charlemagne, we arrive at a trillion ancestors and that is a problem because we now have more ancestors than there were people. Thus one can deduce that a lot of those ancestors must be the same person."
To visualize this concept, Ralph suggests drawing an imaginary family tree. He does this by using DNA data from the whole genome sequencing data on 2,257 people living in more than 40 European populations.
"Our research confirmed what Chang suspected—that everybody who was alive in Europe a thousand years ago and who had children, is an ancestor of everyone alive today who has some European ancestry," Ralph said.
You can read this interesting article at http://phys.org/news/2013-08-dna-earth.html.
My thanks to newsletter reader Paul Roberts for telling me about this article.