People lived in the same villages for gneration after generation. There simply was not anyone else available as marriage partners.
I beleive the biblical account of Mary and Joseph proves that they were cousins as well. All of the begets in the book of Matthew are to show that Jesus would have had an unbroken line of inheritance to Israel's King David were it not under Roman occupation at the time.
Interestly, my wife and I are 12th cousins-- not through shared Cherokee ancestry (who don't have good written records before the 1780s) but through different children of an early Rhode Island colonist named Rev. John Crandall. Most people with early colonial ancestry are, to one degree or another, related.
Hello cousin. All four grandparents of John Crandall’s second wife Hannah Gaylord were my ancestors.