And like Barack Obama, we are all cousins of Dick Cheney.
A little research that once ended my genealogical ambitions to find someone famous in my family:
Under the conditions laid out in his paper, the most recent common ancestor of every European today (except for recent immigrants to the Continent) was someone who lived in Europe in the surprisingly recent past—only about 600 years ago. In other words, all Europeans alive today have among their ancestors the same man or woman who lived around 1400. Before that date, according to Chang’s model, the number of ancestors common to all Europeans today increased, until, about a thousand years ago, a peculiar situation prevailed: 20 percent of the adult Europeans alive in 1000 would turn out to be the ancestors of no one living today (that is, they had no children or all their descendants eventually died childless); each of the remaining 80 percent would turn out to be a direct ancestor of every European living today.
This constant churning of people makes it possible to apply Chang’s analysis to the world as a whole. For example, almost everyone in the New World must be descended from English royalty—even people of predominantly African or Native American ancestry, because of the long history of intermarriage in the Americas. Similarly, everyone of European ancestry must descend from Muhammad. The line of descent for which records exist is through the daughter of the Emir of Seville, who is reported to have converted from Islam to Catholicism in about 1200. But many other, unrecorded descents must also exist.
http://www.gly.uga.edu/railsback/GenealComp1.html
The staggering number of ancestors each of us has (for example, perhaps 200 million of them in 1300 AD) also means that your ancestry is probably more diverse than you think. Somewhere among those 200 million people who were your ancestors in 1300, there are probably some folks who came from places you wouldn’t think likely, or who were members of ethnic groups that would surprise you. You’ll never know who all those 200 million people were, but they can be abundant fuel for your imagination.
http://www.stat.yale.edu/%7Ejtc5/papers/CommonAncestors/NatureCommonAncestors-Article.pdf (PDF)
If a common ancestor of all living humans is defined as an individual who is a genealogical ancestor of all present-day people, the most recent common ancestor (MRCA) for a randomly mating population would have lived in the very recent past (ref). However, the random mating model ignores essential aspects of population substructure, such as the tendency of individuals to choose mates from the same social group, and the relative isolation of geographically separated groups.Here we show that recent common ancestors also emerge from two models incorporating substantial population substructure. One model, designed for simplicity and theoretical insight, yields explicit mathematical results through a probabilistic analysis. A more elaborate second model, designed to capture historical population dynamics in a more realistic way, is analysed computationally through Monte Carlo simulations. These analyses suggest that the genealogies of all living humans overlap in remarkable ways in the recent past. In particular, the MRCA of all present-day humans lived just a few thousand years ago in these models. Moreover, among all individuals living more than just a few thousand years earlier than the MRCA, each presentday human has exactly the same set of genealogical ancestors.
http://humphrysfamilytree.com/ca.html
http://www.elvidge.com/Genealogy/essay1.htm
http://members.aol.com/acadac/gnlgy/cousin.html
Ketchup and Caviar 