The Highlands of Papuan New Guinea is the location of an evidential Sprachbund that includes at least fourteen languages from six language families with grammaticized evidentiality. As with other linguistic features in New Guinea, evidentiality has spread across genealogical boundaries through repeated language contact. In this paper, we examine likely paths of development of the various subsystems and the spread of evidentiality as a whole. The evidence presented here points toward the Engan language family as the most likely source for at least some of the evidential markers and distinctions found in the region, supporting previous suggestions by other researchers.