In 1858, a British naturalist discovered an invisible ‘wall’ near Bali – 5 years later, science changed forever

Stay on the shores of Bali and look to the east. Across the water canal, the island of Lombok sits on the horizon.

This narrow 21-mile stretch of the ocean, known as the Lombok Strait, divides these two islands. A motorbike can make the passage in about an hour, so animals – small, at least – may not have problems to make the journey.

And yet, something stops them. Not a storm. Not a predator. Just an invisible line, keeping them back.

In 1858, British naturalist Alfred Russel Wallace wrote Charles Darwin a letter while burning with fever in a remote hut in the Malaysian archipelago. He had spent years in a row, strictly documenting species throughout the region, but it was in that delightful, maternal noise that the realization struck it: the natural world was not a calm mix of species, but a separate work with invisible obstacles.

One of those barriers – the one that goes through the Lombocke Strait – was most striking of all: Wallace line.

Few animals have ever crossed the Wallace line

Before Wallace’s lucky journey through the Malaysian archipelago in the 1850s, the predominant belief was that the species were static and distributed based on environmental conditions, with little consideration for land historical processes.

Wallace’s meticulous documentation for species distributions destroyed this assumption. He noted that despite their environmental closeness and similarity, the islands of Bali and Lombok had very different fauna.

West of the Wallace line – in Borneo, Sumatra and Java – you will encounter deep Asian roots creatures: tiger, rhinoceros, elephants and primates.

Cross east on the smallest islands of Sunda, Sulawesi and New Guinea, and the faunal landscape is moved to the Australian-Marsupial species, such as the possessions of the trees climb through the forests, Cockatoos and Lorikeets the sky and mammals like echidnas make a look.

What caused this fierce division?

The answer lies below the surface of the ocean. This is ironically suitable, given that Pisces are one of the only animals that freely cross the imaginary line without consequences.

Over the last The age of ice, when the sea level fell, the Earth’s bridges linked many islands of Southeast Asia to the continent, allowing the species to migrate freely.

But the deep waters of the Lombocke strait were never said. It remained a frightening obstacle, preventing the passage of species, leaving two distinct evolutionary worlds to develop independently.

Wallace’s discovery reformulated how the main minds of the time understood evolution – and even pushed Darwin to publish his work faster.

For some species, the Wallace line changed the course of evolution

Makaqe eating crab, or Macaa fascularisA very adaptable primate found west of the Wallace line developed a long tail that helps in the style of its Arbëresh life. Flowering in forests from Thailand to Borneo, it is also successfully integrated into urban environments.

Meanwhile, Macaki brought, or Macaa ochreataFound east of the Wallace line in Sulawesi, evolved a stronger body and a special shorter tail, adaptations suitable for dense island forests and various food sources.

The separation imposed by the Wallace line has formed their behaviors, too; While the macaks that eat crabs are opportunistic and often raid the crops and human settlements, the stuck macaks remain more attractive, relying on the isolated sources of Sulawesi forests.

Sunda Frogmouth (Batrachostomus cornutus), a night bird located in Southeast Asia, belongs to an ancient origin restricted mainly in the Sunda region. Its adaptations make it suitable for life in dense tropical forests, where it relies on an extraordinary camouflage to remain undiscovered.

Meanwhile, on the Australian side of the Wallace line, Frogmouth Tawny (Podargus strigoides) And its relatives have evolved separately, adapting to the opening of forest lands and the most dry habitats.

The divergence between these frogmouth lines dates back to the oligocene, approximately 30-40 million years ago, making it one of the oldest known vertebral divergences across the Wallace line.

This long division suggests that the island bows and the displacement of land masses may have once provided a trail for distribution, only to be isolated later through geological changes.

Happy what happens when a species crosses this invisible limit?

Many animals that evolved on one side of the Wallace line are well allocated in their specific environments. If a tiger somehow made it in smaller Sundas, for example, it can fight in an ecosystem that lacks its biggest articles, it relies on food.

However, some species can bloom if they cross the Wallace line. Released from the pressures of selecting their original environment – such as competitors, predators or diseases – successful colonizers can use new ecological opportunities, like many invading species that bloom in new habitats.

Battery is one of the ground lines that offers some exceptions from this iconic biogeographic boundary. Unlike most terrestrial species, they can traverse water barriers with relative ease during flight. Some stick species, such as flying foxes, are found on both sides of the Wallace line, as they can travel long distances in search of food and turkeys.

Phenomena like the Wallace line highlight the extraordinary variety of life within the natural world. How do you feel about the boundless diversity that nature has to offer? Get a science -backed test to see where you stay in Connection to the degree of nature.