I was on this genealogy list once that was discussing the Thomas Jefferson-Sally Hemmings liason. It was mostly people yelling at each other pro or con what they believed about the genetic tests that basically proved one branch of her descendants shared dna with the Jefferson family.
I pointed out to them that no one was arguing about weather or not John Wayles, Jefferson's father in law, was also the father of Sally Hemmings. No one cared what he did, they were only worried about the third president of the US.
Indeed, everyone we see everyday, we share dna with, share ancestry with, even if it were just a breif encounter long ago. If people could just learn to think that way.