I guess sex with cousins is a big thing in Canada and Australia.
If I remember the stats correctly it is the US that takes that prize.
Though to be fair just about every small population group on the planet would have had the issue, and is probably how we ended up with distinct racial and regional characteristics.
OK got a link? My trips to Canada got me to notice just how many Canuckleheads looked a lot alike. Ugly seems to be a real thing there among the men. Can't tell me some inbreeding didn't occur.