Modern American anthropology owes a lot to one man: Franz Boas, widely regarded as the father of the discipline.
Indeed, before Boas, anthropology in the United States could hardly be called a science. It was carried out by those who believed that some cultures were more evolved than others and that they could be set in a line with cannibals at one end and white Christians at the other. Hardly surprising, since much of the information these proto-anthropologists used came from missionaries or government officials.
Such secondhand data were of no use to Boas, who in the late 19th century went into the field to live with the Kwakuitl Indians on the U.S. northwest coast and see what was going on for himself. In doing so, he gave to anthropologists the idea of empirical data collection. He rejected the idea that some cultures could be superior to others, introducing the idea of cultural relativism. Cultures evolved on their own over a period of time, Boas said, and it was meaningless to rank them.