At the same time, redlining—the federal housing policy of refusing to approve or guarantee mortgages in areas where black people lived—served to deny them access to mortgages in their own neighborhoods. These policies became the pillars of a residential caste system in the North that calcified segregation and wealth inequality over generations, denying African-Americans the chance accorded other Americans to improve their lot.

Even in the places where they were permitted, blacks were relegated to the lowest-paying, most dangerous jobs, barred from many unions and, at some companies, hired only as strike breakers, which served to further divide black workers from white. They were confined to the most dilapidated housing in the least desirable sections of the cities to which they fled. In densely populated destinations like Pittsburgh and Harlem, housing was so scarce that some black workers had to share the same single bed in shifts.

They found a brick three-flat with bay windows in the all-white neighborhood of Woodlawn. Although other black families moving into white neighborhoods had endured firebombings and mob violence, Carl wanted more space for his family and bought the house in secret with the help of progressive white real estate agents he knew. He moved the family late in the spring of 1937. The couple’s youngest daughter, Lorraine, was 7 years old when they first moved, and she later described the vitriol and violence her family met in what she called a “hellishly hostile ‘white neighborhood’ in which literally howling mobs surrounded our house.” At one point a mob descended on the home to throw bricks and broken concrete, narrowly missing her head.

While psychologists can’t know exactly what goes on inside our heads, they have, through surveys and laboratory studies, come up with a set of traits that correlate well with conspiracy belief. In 2010, Swami and a co-author summarized this research in The Psychologist, a scientific journal.