Alfred Russel Wallace, the so-called father of animal geography, formulated his ideas on evolution by natural selection while observing and collecting wildlife in the islands of Southeast Asia. He was particularly impressed by the sudden difference in bird families he encountered when he sailed some twenty miles east of the island of Bali and landed on Lombok. On Bali the birds were clearly related to those of the larger islands of Java and Sumatra and mainland Malaysia. On Lombok the birds were clearly related to those of New Guinea and Australia. He marked the channel between Bali and Lombok as the divide between two great zoogeographic regions, the Oriental and Australian. In his honor this dividing line, which extends northward between Borneo and Sulawesi, is still referred to today as Wallace’s Line.
Other biogeographers have since put the boundary between the Oriental and Australian provinces in slightly different locations. As is true of most regions, the core areas of both provinces are clearly distinct, but things are a little fuzzy on the periphery. Thus some biogeographers recognize the island region between Java and New Guinea as a mixing zone and designate it Wallacea.