Because of pedigree collapse people of the same nationality don’t have to go very far back to find common ancestors. Meiosis is evidently somewhat random, but

Because of pedigree collapse people of the same nationality don’t have to go very far back to find common ancestors. Meiosis is evidently somewhat random, but given enough pairs of people who are cousins many times over and the birthday paradox you’re going to see a lot of doppelgangers.