The Sharp Divide Between Asia and Australia That Animals Rarely Cross

Between the continents of Asia and Australia lies an invisible barrier that animals rarely cross, even those that take to the sky. This seemingly magical barrier is known as Wallace’s Line, and it is responsible for shaping ecosystems on both its western and eastern sides. Each side has a distinct ecosystem with its own separate species. While Australia and New Guinea are home to marsupials and monotremes, Asia has tigers, monkeys, and elephants.

Though Wallace’s Line is not a tangible landmark, it is defined by deep ocean channels, which formed millions of years ago. Distinct ecological climates, each with unique flora and fauna, formed on either side of the line. It has influenced species development by sending animals on opposite sides of the line along separate evolutionary trajectories. DNA studies reveal distinct differences between Asian animals to the west and Australian animals to the east.

This slideshow explores the intriguing and little-known Wallace’s Line, including its exact location, how it was created, and how it has dictated millions of years of animal development. Discover the science behind the powerful barrier responsible for shaping an entire region’s biodiversity.

• Wallace’s Line is an invisible boundary separating Asian and Australian wildlife.
• Naturalist Alfred Russel Wallace first described it in the 19th century.
• Most animals naturally avoid crossing the line, even birds and ocean species.

• The invisible line runs north to south between Bali and Lombok in Indonesia.
• The boundary resulted from shifting tectonic plates, separating Asia and Australia.
• The deep Lombok Strait is a physical feature of this barrier.

• About 30 million years ago, tectonic plates collided and formed new islands and climates.
• Ocean currents were redirected, and deep-sea trenches emerged.
• These changes significantly shaped how animals evolved on each side of the line.

• Asia is home to elephants, tigers, apes, and rhinos.
• Australia and New Guinea hosts marsupials, monotremes, and parrots.
• Very few animal species inhabit both sides of the line.

• Even during low sea levels, deep ocean trenches remain, preventing easy crossing by land animals.
• Climate and habitat play key roles in maintaining the divide.
• Animals often fail to thrive in conditions on the opposite side of the line.

• Even flying creatures like birds and insects show distinct regional differences.
• DNA analysis reveals limited mixing of populations across the line.
• Some species, like bats and monitor lizards, have been known to make rare crossings.

• Scientists now see Wallace’s Line as a gradient rather than a strict border.
• Some species cross or straddle the divide.
• The line helps explain evolutionary patterns.

• New research explores how climate and small islands influenced migration.
• Studies of 20,000 vertebrates support Wallace’s observations.
• Wildlife adapted uniquely to tropical climates versus drier climates on each side.

• The famous divide is a key concept in evolutionary biology and biogeography.
• It shows how geography influences species development.
• The line is used to understand biodiversity and conservation efforts.