"The fact that I followed my great-grandfather into politics is surprising enough," he says. "But the fact that I chose the same sort of politics is more than just coincidence. The odds in favour of that happening by accident must be minuscule." [BBC News, 28 March 2008]Matthew seems to be implying that the Liberal party is a particularly unlikely choice, but of course it wasn't so unusual in his great-grandfather's day. Lots of politicians have Liberal MPs in their family tree, including the Benn dynasty. (Two generations of Liberal MPs followed by two generations of Labour MPs - what odds are the bookies taking for Hilary Benn's four children - four different parties perhaps?)
Meanwhile in the United States, a genealogical organization has discovered family relationships between various unlikely characters. Barack Obama is distantly related to George Bush, Dick Cheney, Winston Churchill, Gerald Ford, Lyndon Johnson and Harry S Truman. (And me, obviously.) For her part, Hillary Clinton is distantly related to Camilla, Duchess of Cornwall (but then who isn't?). [BBC News, 26 March 2008]
Update (October 2008): Sarah Palin and Princess Diana are cousins.
The aristocracy has always had good records of this sort of thing, it being important in some circles to trace your family back to the Norman Conquest or the Pilgrim Fathers, but ordinary mortals are catching up thanks to the Internet, which supports a vast grid of amateur genealogists. And DNA testing is producing a few surprises, including two English women descended from Native Americans. [BBC News 4 May 2007]
But do the mathematics. Some of the people who were alive five hundred years ago have no living descendants at all (thanks Darwin!), while others have millions. So we don't have to go back very far to find common ancestors.
We might also note that an obsession with breeding can produce inbreeding. This helps to explain the congenital ill-health and lack of intellectual prowess in some closely knit groups, including perhaps some branches of European Royalty. And if the latest genealogical research reveals inbreeding among the political classes, that might explain a few things mightn't it?