During the 1920s Robert E. Park (1864–1944) and Ernest W. Burgess (1886–1966) developed a distinctive program of urban research in the sociology department at the University of Chicago. In numerous research projects focused on the city of Chicago, Park and Burgess elaborated a theory of urban ecology which proposed that cities were environments like those found in nature, governed by many of the same forces of Darwinian evolution that affected natural ecosystems. The most important of these forces was competition.