I read a book a few years ago, titled "The Red Queen." It's authors claimed that if you were of british descent, you only had to go back 26 generations to the original community/clan, and that we were all related.

Fascinating book concerning two different phenomena: the advantage of sexual reproduction at the level of individuals, and the constant evolutionary arms race between competing species.

(WARNING! SCIENCE ALERT!)

[link to en.wikipedia.org]