Whites are prone to guilt. Some psychologists attribute this to evolution: i.e., whites evolved in a cold climate that required substantial group cooperation for winter survival, which led to an egalitarian ethic that included guilt as a means to control selfishness. Blacks are easily able to exploit this guilt, especially among progressive whites. In addition, few whites are willing to consider group differences in intelligence, so they fall prey to the “miasma” theory of racism that explains all disparities as the result of an invisible racism.