The Wallace Line

Wallace proposed a theory of evolution at the same time as Darwin, but his contribution to the science of evolution remains less celebrated. The Wallace line is a boundary proposed in 1859 by Wallace to separate the biogeographical realms of SE Asia and Australia. To the west of the Line are found organisms related to Asiatic species; to the east, a mixture of species of Asian and Australian origins exist.

Why is it that the island of Bali is home to Asian birds such as the weaver bird, and the neighbouring island of Lombok, just 24 kilometres away across a narrow strait, echoes to the scream of cockatoos. This extraordinary biological boundary is known today as the Wallace Line. Like his friendly rival and fellow Charles Darwin, Alfred Russel Wallace travelled the world collecting and studying species that were new to science. His legacy is the Wallace Line, a near-magical boundary which doesn’t simply explain where animals live today but provides a key to their evolution. His idea has had a profound effect on all biological thinking to the present day.

The region of Wallace's Line is one of the most geologically complex zones known. Explanations for the extraordinary biogeography of the region are found in the Pleistocene glaciations which resulted in several oscillations of the sea-level where landmasses and their biological contents were linked and severed in turn. Other explanations are found in the present day ecology of the region including the significant and fascinating influence of pre-historic and historic humans including the diminutive Hobbit, Homo floresiensis, and the 2019 discovery of a similarly diminutive Homo luzonensis. More recently Asian Denisovans, who arrived nearly 400,000 years ago seemed to have no trouble with the Wallace Line and left their mark in the DNA of Papuans. Penny will review evidence for the Wallace Line.