Humans basically like to draw lines. Country lines, seas, time, provinces. But there is a line that divides Indonesia without us seeing it. If we stand in Bali and look east, it is in that strait that this narrowest point line appears. 30 km of seemingly ordinary seascape, but with tens of thousands of years of history. The western part is native to Asian animals. Like elephants, tigers, rhinos. Meanwhile, in the eastern part there are Komodo dragons, cockatoos, and birds of paradise. This is the boundary we often call the Wallace line. An invisible biogeographic dividing line that determines the environment of living things. The Wallace Line was first coined in 1859 by a man named, yes, Wallace. woles Alfred Russell Wallace. A British naturalist who prefers the forest to the reading room. At that time, he was traveling around the Malay Archipelago for 8 whole years. He carried a butterfly net specimen box, a worn notebook. And of all that he encountered, there were two big things that continued to haunt his mind. The first is about how species can change. About natural selection. The big idea he got was not in the library, but on his rickety bed while his body was being shaken by malaria fever. The idea then also appeared in England in the head of Charles Darwin, and finally yes, we know who was famous first. But Wallace didn't stop there. Because over the years in the field, he began to see other patterns. A strange pattern, which cannot be explained by evolution alone. Every time he moved islands, he realized. There are changes. Change is not always smooth. Sometimes, the difference between two neighboring islands is greater than the difference between two continents. And the turning point. When he crossed from Bali to Lombok, it was only 32 km. As soon as he landed, the contents of the forest changed completely. Birds common in the west, such as woodpeckers, weaver birds, or certain types of insects, are disappearing. Not reduced, but completely absent. Even though the natural conditions are similar. Similar trees, not much different weather. The types of living creatures he encountered seemed to come from another world. At that moment, Wallace realized. This is something bigger. There is an invisible boundary that divides the animal world in two extremes. As if they know, if you're from the west, you'll only get this far. If you're coming from the east, you can't get through there. And from that point on, he continued to follow the line. From one island to another. Looking for evidence, looking for patterns, looking for reasons. Because the further he went, the line didn't disappear. It's getting clearer. What could make biological boundaries this clear? What divides the two worlds, in the middle of an ocean that from the outside looks calm? Wallace watched that carefully. He realized something deeper was at play. It's not about distance. It's not about the weather. It's not a coincidence either. He began to imagine that the map of life today was a reflection of a much older history of the earth. The land that was once united, then split apart. The sea that was once shallow, then became a ravine. And in the midst of it all, the animals have to choose sides. This line is not only about biology, but also geology. Wallace was one of the first to notice. If you want to know how the earth works, look at where living things live now. What grows, what disappears, and what never crosses over. That's how he read the history of the earth. Not through rocks, but through birds, through insects, through small patterns that hold big stories. Today, this way of thinking has become the basis of science. But in its time, it was crazy. Like lighting up the map in a way that's never been tried before. And by taking this perspective, he concluded that the western islands must have once been connected to each other. Although they are currently surrounded by shallow seas, this is simply a result of geologically recent sea level rises. Otherwise, how could the large animals on that side, such as tigers, rhinos, and tapirs, end up on those islands? Because they are now separated by a stretch of water that is too wide for the species to cross. He had similar thoughts about how the islands to the east of Java and Kalimantan were formed. At least some of them are remnants of the former Australian continent. Wallace had a hunch that amidst all these changes, deeper waters with strong currents lay between the two regions. It must have prevented many species from crossing from one continent to another. Wallace has already put together many pieces of the puzzle. However, there was one big part he hadn't found yet. Something that could explain why everything looks the way it does. Tectonic plates. The idea that the Earth's surface is not something fixed. It consists of large pieces that slowly move. In Wallace's time, such ideas did not exist. It wasn't until the late 1960s that scientists agreed. Continents can move. The seabed can open and close. And invisible lines like the ones Wallace saw could be scars from Earth's geological past. Unfortunately, Wallace never knew that. He died decades before the puzzle was finally complete. We now know that plate tectonics plays a huge role in shaping the Earth's surface. They split and united continents, raised mountains, and created island chains that became homes to millions of living creatures. And of all places in the world, the Malay Archipelago is one of the most geologically complex regions. This is where several large plates meet and push against each other, making this region full of active volcanoes, earthquakes, and huge differences in animal life. Welles didn't know this at the time, but his instincts were right. That both sides of this line were once land masses separated by vast distances. On the west side is Sunda, a continental plate that was once connected to Asia. On the east side, there is Sahul, which consists of Australia, Papua, and the Aru Islands. These two landmasses were once far apart, but slowly, over tens of millions of years, the Australian plate moved northward, taking its distinctive animals with it. Unique birds, reptiles, and marsupial mammals. When the ice age came, sea levels dropped drastically, because a lot of water was locked in ice. Even when shallow seas connected the islands on their respective sides, between them remained a deep gap, which continued to separate the eastern and western worlds. and formed the transitional region we now know as Wallacea. These Wallacea islands are different from the continental islands that flank them. Because the islands were never connected to any larger landmass. They are ecological blank slates waiting to be filled with whatever creatures can get there first. And most of the ones that arrived first were species from Australia. Take the Komodo dragon for example, a giant monitor lizard that currently lives on several islands in NTT. Their fossils first appeared on the Australian mainland more than 3 million years ago, during the Pliocene epoch. Then they only reached their current home in the Wallacea region around 1 million years ago. Until now, deep waters with strong currents, including the Lombok Strait, still limit the spread of many species across this line. Because of this, the differences in their evolutionary history remain so striking. This is the sharp line that divides the forests on the islands. The line was first drawn by Wallace in 1859, and still fascinates biogeographers today. Wallace's invisible line may not be physically real, but it shows how powerful the influence of ancient geological events is on the diversity and distribution of life today. Darwin is perhaps best known as the man who explained how species arose. But Wallace is still recognized as a pioneer in understanding why species appear in certain places. For those of you who are still enthusiastic, now explain what you think is the difference between Wallace's line and Weber's? in the comments column!