So what you are saying is that someplace like Arkansas is similar to the garden of eden because brothers and sisters get married..........
Humor aside, if you start from one couple, what other choice do you have?
Whether you believe the first humans came about as the Bible states or as a genetic mutation via evolution, you would have to have your first couple who are in all likelyhood very, very closely related (perhaps, siblings, perhaps father/daughter or mother/son) in order to solidify that mutation. Evolution clearly dictates we all have the same mother at some point in the past, doesn't it? IIRC they even dated when that common ancestor lived using mytocondrial (SP?) DNA.