Are You My Cousin? According to a famous genealogist, you are.
Megan Smolenyak explains that each of us has two parents, four grandparents, eight great-grandparents and so on. If you go back 30 generations you would have more ancestors than the population of the earth at that time.
The explanation is of course "pedigree collapse". When cousins intermarry the number of ancestors declines in each prevoius generation. Read the full article.
Other articles and books by Megan Smolenyak:
Trace your roots with DNA : using genetic tests to explore your family tree
Who Do You Think You Are?: The Essential Guide to Tracing Your Family History
Find this article at http://thelibrary.org/blogs/article.cfm?aid=583&lid=50&view=print