She found that between ages 4 and 11, upper-middle-class children from mostly white neighborhoods around Boston increasingly viewed race as a permanent condition and expressed stereotypes about other racial groups: that blacks were aggressive or, on the flip side, good at basketball; that Asians were submissive and good at math. These children came from public schools in liberal areas. They probably weren’t deliberately taught these stereotypes at home. But they absorbed them from the American ether nonetheless.

Would children in Hawaii express the same views? Dr. Pauker repeated the study with middle- and upper-middle-class grade-school students in and around Honolulu, and was not entirely surprised to find that in Hawaii, the children, including those who were white, tended not to express the same essentialist ideas about race. They were not race-blind. They recognized skin color, hair texture and other features commonly associated with race. But they did not attribute to race the inherent qualities — aggression or book smarts — that their mainland brethren did. “They didn’t believe that race was biological,” Dr. Pauker told me.

She had a hypothesis to explain the difference. Whites dominated in the Boston area schools, but were a minority in Hawaii, and always had been. Hawaii also had the highest percentage of mixed-race people by a long shot in the country. (Among them was our first mixed-race president, Barack Obama, who was born there.) Mixed-race people, who make up nearly a quarter of Hawaii’s population of 1.4 million, serve as a kind of jamming mechanism for people’s race radar, Dr. Pauker thinks. Because if you can’t tell what people are by looking at them — if their very existence blurs the imagined boundaries between supposedly separate groups — then race becomes a less useful way to think about people.