In his early writings Max Horkheimer explored the issues surrounding biological explanation in Kantian and neo-Kantian philosophy. After he became director of the Institut für Sozialforschung in 1930, he continued to explore the relationships between biology, materialism, philosophy, and social theory. This interest was reflected both in his editorial policy for the Zeitschrift für Sozialforschung and in his own scholarly development that led to the development of critical theory in the later 1930s and the anti-Semitism research of the 1940s. Horkheimer's interests and ambitions also generated resistance from other social scientists. The Berlin ethnologist Richard Thurnwald, along with his student and colleague Wilhelm Emil Mühlmann, came into direct conflict with Horkheimer—and with each other—over the significance of biology for social research. This conflict with Horkheimer further ignited a vigorous debate between Thurnwald and Mühlmann about a concept that also became a central issue in Horkheimer's thought and editorial practice: race. Thurnwald had begun his career as a founder of the German Society for Racial Hygiene, but by the 1920s he had developed into a vocal critic of what he saw as the reductive pseudo-Darwinism of racial hygiene and eugenics.