Some people (especially those who are American and on this site) who push back on the “racial purity doesn’t exist” idea usually lean on the belief that isolated populations over long periods created distinct genetic traits—like skin tone, facial features, or certain inherited diseases. They’ll argue that these populations stayed separate long enough (like in ancient Europe, Africa, Asia, etc.) to form what they consider “pure” lineages or races. So to them, if someone’s lineage is untouched by mixing for centuries, that’s “racial purity.” Like for example BLACK people being worse at swimming but better at running. Which is a genuine fact of their bone structure.