It has focused on human behavior as shaped by social structures and physical environmental factors, rather than genetic and personal characteristics. Biologists and anthropologists had accepted the theory of evolution as demonstrating that animals adapt to their environments. As applied to humans who are considered responsible for their own destinies, members of the school believed that the natural environment, which the community inhabits, is a major factor in shaping human behavior, and that the city functions as a microcosm: "In these great cities, where all the passions, all the energies of mankind are released, we are in a position to investigate the process of civilization, as it were, under a microscope."[2]