Crossing The Wallace Line

If you’re travelling by speedboat from Bali to Lombok’s Gili Islands, you might find yourself gripping ever more tightly onto your seat as the sea begins to swell and the waves begin to balloon. It can be a scary ride.

The Lombok Straits that divide the Indonesian islands of Bali and Lombok stretch to more than a kilometre deep. The straits are a narrow, rowdy meeting point where the warm Pacific Ocean squeezes herself into her colder Indian cousin. The deep channel that separates Bali from Lombok also happens to be home to one of the most important imaginary lines in the world: The Wallace Line. It follows the subterranean fault lines: from the southern reaches of Bali and Lombok up to the deep Makassar Straits that split Sulawesi and Borneo.

Alfred Russel Wallace: The ‘Father of Biogeography’

It was Alfred Russel Wallace (1823-1913) who drew this thin line that changed forever how humans think about themselves. Lanky, short-sighted, bearded and gentle, this eccentric English naturalist had already established a business of collecting and selling natural history specimens – butterflies, beetles and exotic birds – from a four-year trip around the Amazon before he rolled up onto Indonesia’s shores in 1854.

Wallace spent eight years zig-zagging what was then known as the Malay Archipelago, wallowing in the islands’ sensationally varied wildlife and travelling by steamer to schooner to dug-out canoe in his obsessive search for the perfect specimen.

Alfred Wallace portrait
Alfred Russel Wallace (1823-1913), creator of The Wallace Line.

Crossing the Wallace Line

But it was at the end of his bumpy boat ride across the Lombok Straits where Wallace had his lightbulb moment that would change the course of human history. Stepping onto the steep beach at Ampanan in Lombok, he expected to hear the sounds of woodpeckers, fruit-thrushes and oriental barbets that he had heard so often in Malaysia, Borneo and Bali. Instead he was met with the piercing calls of the helmeted friarbird – an Australian honeyeater. Inland, the Lombok forests rang with honeysuckers, cackling brush-turkeys and the strangled screams of Australian cockatoos.

Something wasn’t quite right.

How could birds, animals, reptiles and plants change so dramatically in the space of some 25 kilometres? After all, the distance between Bali and Sumatra was far greater, but the two islands still shared the same flora and fauna. Why weren’t the tail-feathers of every Papilio androcles as long and as white as every other? And why did certain species only exist in specific habitats, cut off by this invisible, biogeographical line?

Wallace wrote in his landmark book of 1869, The Malay Archipelago:

‘It is well known that the natural productions of Australia differ from those of Asia more than those of any of the four ancient quarters of the world differ from each other. Australia in fact stands alone: it possesses no apes or monkeys, no cats or tigers, wolves, bears or hyenas; no deer or antelopes; no sheep or oxen; no elephant, horse, squirrel or rabbit. Instead of these, it has marsupials only, kangaroos and opossums, wombats and the duck-billed platypus. In birds it is almost as peculiar.’

BBC Programme written and presented by Bill Bailey following in the steps of Alfred Russel Wallace in Indonesia.

The Wallace Line Role in The Birth of the Theory of Evolution

Wallace had stumbled upon the theory of evolution. While his contemporary Charles Darwin was sitting comfortably in his English mansion trying to figure the same puzzle out on paper, Wallace – a largely self-educated man from a humble background – was tramping through jungles, healing his tropical ulcers and suffering bouts of malaria to reach the same conclusion. Namely that:

‘… the Western part [of Indonesia is] a separated portion of continental Asia, the Eastern the fragmentary prolongation of a former pacific continent…’

Wallace hadn’t only found the key to evolution as he crossed his own imaginary line. He had also inadvertently worked out what had been happening within the earth’s tectonic plates several kilometres below his tired feet for the past several million years.

Plate Tectonics and Continental Drift

The world’s continents haven’t always been separate. Just as Africa and South America had been one massive land mass in the distant past, so too had the continents of Asia and Australia. At this point on the Geologic Time Scale, species were free to come and go. Nothing divided them, and there was no need to further divide into sub-species.

However, the earth is a restless thing. You only have to step back 17,000 years or so ago when the last Ice Age lowered the planet’s sea levels by over a hundred metres. At this time, Java and her little sister Bali became one – the seas in the Bali Strait are shallow. But the seas of the Lombok Strait – with depths ranging from 800 to 1,000 metres-plus – never went away.

As tectonic plates shifted and battled themselves deep below the earth’s surface, continental drift saw the land tear itself apart to create deep bodies of water that separated animals and plants from their native environment. With gradual changes in temperature and weather, these core species were forced to subdivide in order to continue to exist.

In a word? Evolution.

Wallace Line
Wallace Line (“Map of Sunda and Sahul 2” by Altaileopard – Own work. Licensed under CC BY-SA 3.0 via Wikimedia Commons)

The Wallace Line: Conclusion

Perhaps God was dead. Perhaps he wasn’t. But through obsessive observation on the ground, Wallace doggedly mapped these subterranean fault lines that continue to separate animals, plants, Mankind and the planet – some 70 years before oceanographers and sonar came to exactly the same conclusions.

The revolutionary Wallace Line follows these same subterranean fault lines: from the southern reaches of Bali and Lombok up to the deep Makassar Straits that split Sulawesi and Borneo. Trip through Indonesia and see the invisible for yourself: you’ll find orangutans, rhinoceros and pygmy elephants in Kalimantan and Sumatra. But you won’t find any Komodo Dragons on Bali.

The modest Wallace – after years of lonely, dedicated wandering from the Amazon to Borneo – found it hard on his return to adapt to English life after rubbing shoulders with Dayak head-hunters and chasing his beloved birds of paradise.

Alfred Russel Wallace left this life as he had entered it: passionate, obscure and poor. But he had changed the history of the world.