I was reading this article on Slate. Basically it was talking about how in the controversial Davinci Code, people are literal descendants of Jesus. If this were true (who knows), then pretty much anyone alive today would be related to him. The idea presented is that as you go back in time, there are fewer people, so after a few 1000 years everyone has the same set of ancestors from that time no matter where they live.
I've seen something similar to this in my family's own genealogy. From lines that go back far enough, they're all related. (Of course, my sample is skewed because there are very few lineages that go back very far because there are so few records. )
And, of course, we're all related through Adam and Noah :)