• A bio-geographical boundary separating the eco-zones of Asia and Australia.
• It was identified by British explorer Alfred Russel Wallace in 1863 during his explorations.
• It is an imaginary line that intersects the Lombok Strait between the Indonesian islands of Bali and Lombok to the south, and extends north through the Makassar Strait between Kalimantan (Borneo) and Sulawesi.

• Divides species with distinct evolutionary histories.
• Asiatic species (tigers, elephants) are found to the west; Australian fauna (kangaroos, marsupials) dominate the east.
• Despite their geographical proximity, these species evolved separately.

• Birds and mammals are particularly influenced, with few species crossing the line.
• Flora is less affected, though species like Eucalyptus stay on the Australian side.

• While the Wallace Line is a barrier for terrestrial species, it doesn’t stop marine life. 
• The area between the Wallace Line and the Sahul Shelf (near Australia) is known as the Coral Triangle, the most biodiverse marine environment on Earth.

• Result of Australia’s drift from Antarctica and subsequent collision with Asia around 35 million years ago.
• Climate shifts led to cooler, drier Australia and tropical Asia.
• This collision created a deep-water channel that still acts as a natural barrier for species migration.

• During the Pleistocene epoch, lower sea levels exposed land bridges.
• Deep waters between Asia and Australia prevented species migration, maintaining the boundary.

Note: 

Weber Line more accurately defines the balance point where the influence of Asian and Australian species is nearly equal, whereas the Wallace Line marks a sharper divide.