He realized that because bigger populations have more people they are more likely to have a higher number of very smart individuals. He also applied his beliefs to primitive societies, arguing that they too had individual variation. In Primitive Society (1920) he argues "that mental processes are not only comparable but identical in the simpler and the higher civilizations." His interests were always primarily in culture and psychology. He specifically studied issues in race, environment, nature, and relationships. He believed that people were different, but he did not believe that one race was superior to others even though this belief was common during WWII when he was alive.