 In "The Theory of the Leisure Class", Thorstein Veblen explained economic behavior in terms of social influences such as "emulation," where some members of a group mimic other members of higher status.In "The Metropolis and Mental Life" (1903), early sociologist George Simmel referred to the "impulse to sociability in man", and sought to describe "the forms of association by which a mere sum of separate individuals are made into a 'society' ".Other social scientists explored behaviors related to herding, such as Sigmund Freud (crowd psychology), Carl Jung (collective unconscious), Everett Dean Martin (Behavior of Crowds) and Gustave Le Bon (the popular mind).