In the mid 1800s the Malay Archipelago was a wild place. The jungles were thick with wildlife, snakes, lizards, gorillas, and a lone naturalist who was cataloguing as much as he could.
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From 1854 to 1862, Alfred Russel Wallace travelled to what is now Singapore, Malaysia, Indonesia and New Guinea.
Wallace recorded thousands of varieties of animals and plants, making a significant contribution to science. He collected specimens for his private collection, museums and other amateurs.
Some of his ideas we'd find distasteful, such as where he referred to "higher civilisations" (ie his own). Or where he'd shoot animals including orangutans, which he then dried and stuffed for his collection.
Still, Wallace is remembered (with Charles Darwin) for discovering the principles of evolution.
Although Wallace called himself a naturalist, he ranged over everything from botany to zoology and geology.
He also made a remarkable observation leading to what we now call the Wallace Line.
That line, which is only 25 kilometres wide, runs from Bali north-west to past Mindanao and through the strait between Bali and Lombok.
On one side, the animals are exclusively of Asian origin, but on the other they're a mix of both Asian and Australian.
In Wallace's day, the idea of continental drift had not yet been formed. However he did have the emerging sense of deep geological time, using the distribution of species to infer how land has changed over many thousands of years.
Without knowing about the horizontal movement of land surfaces driven by geological convection, he imagined land rising and falling. Land once joined has been divided by sea, and vice versa.
He could see the connection between land separated by water, providing evidence that they were once joined.
While that was a key insight as to why the divide occurs, it's not sufficient.
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Now it appears that changing climate is also implicated. Modelling suggests that drifting contents affected ocean currents, which in turn cooled global temperature.
Many Australian species didn't spread further north because they were less well adapted to the warmer and wetter climate on the Asian side.
Wallace was indeed a curious character and in 1904 wrote a statement that still seems true today: "Turning to the Earth and the other planets of the Solar System ... led to the conclusion that no other planet was likely to be the seat of organic life, unless perhaps of a very low type."
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