Years ago the royals all inter-married to control lands and keep power.

Also years ago people did not travel much. Two hundred years ago a person lived and died often without traveling more then 10 miles from their birth place.

Many Amish are interbred they are all called Yoder, Miller, and there is a third name that escapes me now. But there is a small pool of maybe a few hundred in some places here and they interbreed.

Even today most people marry someone within a 30 mile radius.

Jeff Foxworthy told a really funny joke

You might be a redneck if you go to a family reunion to pick up chicks.