The world is full of wood piles.
LOL! Well said.
Genealogists must rely on documents, and no matter how well documented an ancestral line is, documentation cannot take into account such possibilities as babies switched at birth (remember Puddinhead Wilson?), maternal infidelity (anybody see the HBO series Rome?), clerical errors, etc.
Nucleic acid has changed all this to some extent, and will probably change it even more.
Years ago, when I was a resident (physician) I was called upon to help resolve a paternity suit.
We explained the ABO system and how the man could not be the father of the child because his blood type was AB, his wife's was A, and the child's was O.
The man registered doubt and then said: "If that's true, how come my mother's blood type is A, my father's O, and mine is AB?