The late prehistoric period is crucial to the study of anthropology, as the area of Island Melanesia has provided the world with one of its great anthropological stereotypes, the "Big Man" society. This was developed by Sahlins (1963) on the basis of Oliver's (1955) ethnography of the Siwai of southern Bougainville as observed during the late 1930s. It has led to a gross ethnographic oversimplification of Melanesia as having Big Man societies, contrasted with Polynesia having chiefly societies. Where chiefs were found in Melanesia, their presence has often been interpreted as a cultural borrowing under Polynesian influence (Spriggs 1993 : 198).