"The longer ago somebody lived, the more descendants that person is likely to have today. Humphrys estimates that Muhammad, the founder of Islam, appears on the family tree of every person in the Western world."
http://www.washingtonpost.com/wp-dyn/content/article/2006/08/12/AR2006081200607_pf.html

The meek inherit the earth, I suppose. And if Jesus had any descendants living today [as claimed by the Da Vinci Code], then that also means practically everyone would be His descendants.
And of course the earlier you go in time then more universal it is for every person on earth- for instance with Moses or say the pharaohs of Eygpt. If it could discovered that anyone say 10,000 years ago has one descendant living today, that means there is very high probablity that everyone is a descendant of that same ancient person- whether that person is a mighty king or goat herder.