The Wallace Line

Painting of Wallace's Flying Frog from Sarawak by Wallace (1855) Copyright: AR Wallace Memorial Fund

On this day in 1913, the famous naturalist and biogeographer Alfred Russel Wallace died at his home at the grand age of 90 years.

He's probably best known, although not always credited, for independently proposing a theory of evolution due to natural selection alongside Charles Darwin.

Wallace's biogeographical work is particularly interesting. In the 19th century, he was considered a leading expert in the geographical distribution of animals, so  much so that he is known as the 'father of biogeography'.

Wallace travelled the world studying animal species in their own environments, including trips to South America and the Malay Archipelago (Malaysia and Indonesia). He was one of the first prominent scientists to raise concerns over the impact humans were having on the natural environment.

While on an almost decade long tour of the Malay Archipelago, Wallace discovered what is now known as the the Wallace Line. The imaginary line runs through what is now Indonesia, between Borneo and Sulawesi. To the west of this line, organisms are related to Asiatic species. To the east, a mixture of Asian and Austrailian organisms can be found.

When Wallace published his findings he was puzzled that islands little more then 22 miles apart could have profoundly different animal communities. It was to be almost 100 years before plate tectonics (the movement of parts of the Earth's crust) would be fully understood.

In fact, Wallace's line corresponds very closely to the boundary between two continental plates which were once very far apart indeed.

Biogeography is the study of why we find different organisms in different parts of the world. What is clear though is that history (on the geological timescale) is also important if we are to fully understand this distribution.