Ray Caruth’s daughter was of black/eastern European Jew ancestry. When she got diagnosed with a rare form of leukemia, the family scrambled to find blood donors with similar parentage. Unfortunately, I believe the quest was unsuccessful and she died.
When I donated blood in college, I was signed up for the African American Bone Marrow registry. For whatever reason, black people don’t sign up in high numbers, thereby putting black patients in need of a bone marrow up a creek.
On the news last week, there was a story about an Indian-American woman who was in dire need of a bone marrow transplant. Her friends were going to Indian communities to sign people up.
Race does not exist in a biological sense, but populations do. We don’t mate randomly, and we’re more likely to mate with someone who looks like us (and share our culture, etc.) Sometimes it happens that race is a good proxy for population.