Named for the 19th century explorer-naturalist Alfred Wallace, Wallace's Line is at the heart of the sprawling Indonesian archipelago, one of the world's richest storehouses of biological diversity--both on land and under water.
Turning away from Wallace's Line, I see another dividing line.
Marine ecologists, who study the interrelationships among living things in the sea, have recently proposed the existence of an underwater Wallace's Line, oddly enough, perpendicular to the original north-south line.
Spreading east from Wallace's Line, Wallacea is a sort of no-man's land between Asian and Australian realms, the exclusive home of many strange creatures like the dragons of Komodo, the dwarf buffalos of Sulawesi, and the megapode birds of the Moluccas.
Wallace's Line is one of the biggest biogeographic barriers that is formed by a powerful marine current along the east coast of Borneo.
How the Denisovans got to Australia has remained a mystery and scientists now believe they must have somehow managed to get across Wallace's Line and then interbred with modern humans.
Alan Cooper of the University of Adelaide in Australia and Chris Stringer of the Natural History Museum in the UK have suggested the Denisovans crossed Wallace's Line in an opinion article published in Science.