While stuyding in the Malay Archipelago, Alfred Russel Wallace studied wildlife of the area. He noticed a vast difference among bird species when he crossed from the island of Bali to the island of Lombok. The birds on Bali appeared to be more closely related to the ones on the island of Java and Malayasia, whereas the birds on Lombok were more similiar to the ones on New Guinea and Australia. It was this that led to him dividing the islands in to two zoogeographic areas: the Oriental and the Australian. This divide was made with an invisible line, named after Wallace: "Wallace's Line"
Researchers since Wallace's time have debated where to split the zoogeographpic areas slightly. The area most up for debate is the periphery of the line. Therefore, scientist have grouped an area of islands together and dubbed them "Wallacea." This area includes Sulawesi, the Mollucas, Banda Islands, and the Lesser Sundas.