### **The Invisible Border Between Two Animal Worlds**
There is an invisible line that divides the animal world into two parts, and most birds, fish, and animals cannot cross it. This line is called the **Wallace Line**, and it lies between Asia and Australia. It is named after **Alfred Russel Wallace**, a British scientist and explorer who discovered it in 1859 while exploring the **Malay** Islands.
As he traveled through dense forests, climbed hills, and sailed on boats, Wallace noticed a strange difference. On the west side of the line, such as in Borneo and Sumatra, he saw animals that were typical of Asia, such as **large rhinoceroses, monkeys, and many other tropical forest animals**. But just across the border, in Sulawesi or Lombok, he found **animals that are closely related to those in Australia**, including **colorful birds like cockatoos**.
### **Why Can’t Animals Cross the Wallace Line?**
Some animals can easily move across obstacles like oceans, while others can’t. For example, **bats can fly across the ocean**, but large land animals like elephants are restricted to certain ranges. Some shy birds, which prefer to hide in bushes, also don’t dare fly over large bodies of water because they don’t have safe shelter.
Plants aren’t as affected by the Wallace Line as animals, because they have their own methods of dispersal, such as wind, water, or animals carrying their seeds far away. For example, **eucalyptus trees** are mainly found on the Australian side, but one species is found in the Philippines.
Under the ocean, the Wallace Line doesn’t have much of an impact, either, as the area between it and Australia is known as the **Coral Triangle** – one of the world’s richest marine ecosystems.
### **The Science Behind the Wallace Phenomenon**
After more than 150 years, scientists believe they have found an explanation for this mystery. It all started about **35 million years ago**, when **Australia broke away from Antarctica** and gradually moved north, colliding with Asia. This process created the **Malay Archipelago**, where climate and environmental conditions changed dramatically, affecting the distribution of animal species.
Researchers used **computer simulations** to track the behavior of more than **20,000 animal species** in the past. As Australia moved, a powerful ocean current called the **Antarctic Circumpolar Current** formed around Antarctica, radically changing the Earth’s climate.
In Indonesia, the climate **remained warm and humid**, allowing Asian animals to migrate from island to island in **jumps**. In contrast, Australian animals were accustomed to drier, colder environments, making it difficult to adapt to tropical islands.
### **Other Natural Boundaries**
After Wallace, other scientists also attempted to describe the biological boundary between Asia and Australia. One example is the **Weber Line**, which lies slightly off the Wallace Line. It marks the **Wallacea** region, a series of islands separated from the Asian and Australian continents by deep seas. Since they were never connected to a major continent, the animals there have a **unique mix of Asian and Australian**.
Another major migration event in history occurred in the Americas. About **30 million years ago**, South America **separated from Antarctica and Africa**, causing animals there to evolve in their own unique way. South American species include **giant sloths, giant rodents (capybaras), pangolins, anteaters, and many giant birds of prey**.
Meanwhile, North America was still connected to other regions via the **Bering Strait**, allowing animals there such as **deer, bison, horses, camels, mammoths, and bears** to migrate to many places.
About **3 million years ago**, North and South America were connected via the **Isthmus of Panama**, starting a great exchange of animals known as the **Great American Interchange”**. At that time, animals such as **lynx, jaguars, wolves and bears** migrated south from North America, while **giant sloths and many other South American mammals** migrated north.
However, after the Ice Age, many large South American animals could not adapt to the new environment and became extinct. Meanwhile, many North American animals survived and continued to thrive. Today, some species such as **armadillos, porcupines and opossums** from South America still live in North America, but species such as **jaguars, camels and Andean bears** have long since disappeared from the region.
Scientists believe that **studying how animals adapted to climate change millions of years ago** can help us predict how they will cope with environmental changes today.
