Australasia is a region in the Southern Hemisphere that includes Australia, New Zealand, and neighboring islands in the Pacific. Depending on the context, the term can refer to a geographic area, a biological zone with unique wildlife, or a cultural and sporting grouping. The boundaries shift based on who is using the word and why, which is part of what makes it a surprisingly slippery term.
Where the Term Comes From
The French scholar Charles de Brosses coined the word “Australasia” in the mid-1700s as part of a broader effort to divide the southern Pacific into named regions. Writing during the French Enlightenment, de Brosses split what he called the “fifth part of the globe” into zones he named Australasia and Polynesia. The word itself combines the Latin “australis” (southern) with “Asia,” essentially meaning “south of Asia.” Over the following centuries, the term stuck but its precise boundaries never settled into a single agreed-upon definition.
What Australasia Includes
At its narrowest, Australasia means Australia and New Zealand. This is the most common everyday usage, especially in business, media, and sports. A broader geographic definition pulls in Papua New Guinea, the eastern islands of Indonesia, and various Melanesian island groups like New Caledonia and Fiji. Some definitions also include the smaller Pacific islands that sit on or near the Australian tectonic plate.
The confusion comes from the fact that geographers, biologists, and cultural organizations all draw different lines. A geographer might define Australasia by tectonic plates, a biologist by where certain species live, and a sports federation by which countries choose to compete together. None of these maps overlap perfectly.
The Geological Story
Australia sits at the core of the region’s geology. Much of its western plateau has existed as a landmass for more than 500 million years, built on ancient rock formations called cratons. The continent broke away from the southern supercontinent Gondwana and began drifting north as an isolated landmass between about 55 and 10 million years ago. It continues moving north by roughly seven centimeters per year.
That long isolation shaped everything about the region. Australia’s landscape is largely the result of prolonged erosion by wind and water rather than dramatic mountain-building. The Eastern Highlands (the Great Dividing Range) were uplifted to separate rivers flowing inland from those flowing to the Pacific, and volcanic hotspots created formations across the eastern coast. Meanwhile, the Nullarbor Plain in the south is literally an uplifted ancient sea floor, made of limestone from the Miocene epoch. New Zealand, by contrast, sits on the boundary of two tectonic plates, giving it a far more mountainous and geologically active character.
The Wallace Line
One of the most important boundaries in biology runs right through the waters between Southeast Asia and Australasia. The naturalist Alfred Russel Wallace noticed in 1863 that the animals on either side of a line through the Indonesian archipelago were strikingly different. West of the line, you find Asian species: monkeys, tigers, and woodpeckers. East of it, the fauna shifts dramatically toward marsupials, parrots, and other distinctly Australasian groups.
This boundary, now called the Wallace Line, reflects tens of millions of years of continental separation. Even when sea levels dropped during ice ages, deep ocean channels in this zone kept the landmasses apart, preventing most animals from crossing. The transitional zone between the two realms, known as Wallacea, includes islands like Sulawesi and Lombok where species from both sides mix to varying degrees. The Wallace Line remains one of the sharpest biological boundaries on Earth and is central to understanding why Australasia’s wildlife looks so different from the rest of the world.
Wildlife Found Nowhere Else
Australia alone supports nearly 600,000 native species, and an extraordinary proportion of them are endemic, meaning they exist nowhere else. About 85% of Australia’s plant species fall into this category. The continent is home to half of the world’s marsupial species, including kangaroos, koalas, wombats, and possums, plus the egg-laying platypus and echidna, which belong to an even more ancient mammalian lineage.
New Zealand’s isolation produced its own set of unique species, most famously flightless birds like the kiwi. Without native land mammals (apart from bats), birds and reptiles filled ecological roles that mammals occupy elsewhere. New Zealand’s tuatara, a reptile whose closest relatives went extinct with the dinosaurs, is one of the most distinctive animals on the planet.
This uniqueness comes with vulnerability. Terrestrial mammals across Australia have experienced high rates of extinction, with 10% of endemic species lost over the past 200 years. Two biodiversity hotspots, southwestern Australia and the forests of eastern Australia, contain enormous concentrations of endemic plants but have also suffered exceptional habitat loss. Two species found only on Christmas Island, the blue-tailed skink and Lister’s gecko, now survive only in captivity.
Climate Across the Region
Australasia spans an enormous range of climates. Australia’s size and geography create everything from tropical monsoon conditions in the north to temperate and cool maritime climates in Tasmania. The vast interior is arid or semi-arid, making Australia the driest inhabited continent. Rainfall varies wildly, from over 4,000 millimeters a year in parts of tropical Queensland to under 150 millimeters in the central deserts.
New Zealand’s climate is milder and wetter overall, shaped by its narrow landmass and surrounding ocean. The Southern Alps create a dramatic rain shadow, with the west coast receiving heavy rainfall while the eastern plains stay relatively dry. Papua New Guinea, at the northern edge of the region, is equatorial, with consistently warm temperatures and heavy tropical rainfall year-round. This climatic diversity is one reason Australasia supports such a wide range of ecosystems, from coral reefs and rainforests to alpine grasslands and deserts.
Australasia as a Cultural and Sporting Identity
The term has historically carried a political and cultural dimension as well. In the early 20th century, Australia and New Zealand competed as a combined “Australasia” team at the 1908 and 1912 Olympic Games. The two countries also won the Davis Cup together as Australasia in 1907, 1908, and 1909. This joint identity faded as both nations developed stronger independent identities, but the term persists in business and media, where “Australasia” or “Australasian” commonly refers to Australia and New Zealand as a combined market or cultural unit.
In broader geopolitical contexts, the term sometimes overlaps or competes with “Oceania,” which typically casts a wider net to include all Pacific Island nations. Which word gets used often depends on the speaker’s purpose: Australasia tends to center Australia and New Zealand, while Oceania gives more equal weight to the Pacific Islands.