
The Wallace Line or Wallace's Line is a faunal boundary line drawn in 1859 by the British naturalist
Alfred Russel Wallace
Alfred Russel Wallace (8 January 1823 – 7 November 1913) was an English naturalist, explorer, geographer, anthropologist, biologist and illustrator. He independently conceived the theory of evolution through natural selection; his 1858 pap ...
and named by the English biologist
Thomas Henry Huxley
Thomas Henry Huxley (4 May 1825 – 29 June 1895) was an English biologist and anthropologist who specialized in comparative anatomy. He has become known as "Darwin's Bulldog" for his advocacy of Charles Darwin's theory of evolution.
The stor ...
.
It separates the
biogeographic realm
A biogeographic realm is the broadest biogeography, biogeographic division of Earth's land surface, based on distributional patterns of terrestrial animal, terrestrial organisms. They are subdivided into bioregions, which are further subdivid ...
s of
Asia
Asia ( , ) is the largest continent in the world by both land area and population. It covers an area of more than 44 million square kilometres, about 30% of Earth's total land area and 8% of Earth's total surface area. The continent, which ...
and '
Wallacea
Wallacea is a biogeography, biogeographical designation for a group of mainly list of islands of Indonesia, Indonesian islands separated by deep-water straits from the Asian and Australia (continent), Australian continental shelf, continental ...
', a transitional zone between Asia and
Australia
Australia, officially the Commonwealth of Australia, is a country comprising mainland Australia, the mainland of the Australia (continent), Australian continent, the island of Tasmania and list of islands of Australia, numerous smaller isl ...
formerly also called the
Malay Archipelago
The Malay Archipelago is the archipelago between Mainland Southeast Asia and Australia, and is also called Insulindia or the Indo-Australian Archipelago. The name was taken from the 19th-century European concept of a Malay race, later based ...
and the Indo-Australian Archipelago (Present day
Indonesia
Indonesia, officially the Republic of Indonesia, is a country in Southeast Asia and Oceania, between the Indian Ocean, Indian and Pacific Ocean, Pacific oceans. Comprising over List of islands of Indonesia, 17,000 islands, including Sumatra, ...
). To the west of the line are found organisms related to Asiatic species; to the east, a mixture of species of Asian and Australian origins is present. Wallace noticed this clear division in both land mammals and birds during his travels through the
East Indies
The East Indies (or simply the Indies) is a term used in historical narratives of the Age of Discovery. The ''Indies'' broadly referred to various lands in Eastern world, the East or the Eastern Hemisphere, particularly the islands and mainl ...
in the 19th century.
The line runs through
Indonesia
Indonesia, officially the Republic of Indonesia, is a country in Southeast Asia and Oceania, between the Indian Ocean, Indian and Pacific Ocean, Pacific oceans. Comprising over List of islands of Indonesia, 17,000 islands, including Sumatra, ...
, such as
Makassar Strait
Makassar Strait () is a strait between the islands of Borneo and Sulawesi in Indonesia. To the north it joins the Celebes Sea, while to the south it meets the Java Sea. To the northeast, it forms the Sangkulirang Bay south of the Mangkalihat P ...
between
Borneo
Borneo () is the List of islands by area, third-largest island in the world, with an area of , and population of 23,053,723 (2020 national censuses). Situated at the geographic centre of Maritime Southeast Asia, it is one of the Greater Sunda ...
and
Sulawesi
Sulawesi ( ), also known as Celebes ( ), is an island in Indonesia. One of the four Greater Sunda Islands, and the List of islands by area, world's 11th-largest island, it is situated east of Borneo, west of the Maluku Islands, and south of Min ...
(Celebes), and through the
Lombok Strait
The Lombok Strait () is a strait of the Bali Sea connecting to the Indian Ocean, and is located between the islands of Bali and Lombok in Indonesia. The Gili Islands are on the Lombok side.
Its narrowest point is at its southern opening, with a ...
between
Bali
Bali (English:; Balinese language, Balinese: ) is a Provinces of Indonesia, province of Indonesia and the westernmost of the Lesser Sunda Islands. East of Java and west of Lombok, the province includes the island of Bali and a few smaller o ...
and
Lombok
Lombok, is an island in West Nusa Tenggara province, Indonesia. It forms part of the chain of the Lesser Sunda Islands, with the Lombok Strait separating it from Bali to the west and the Alas Strait between it and Sumbawa to the east. It is rou ...
, where the distance is strikingly small, only about 35 kilometers (22 mi), but enough for a contrast in species present on each island.
The complex biogeography of the Indo-Australian Archipelago is a result of its location at the merging point of four major tectonic plates and other semi-isolated microplates in combination with ancient sea levels. Those caused the isolation of different
taxonomic groups on islands at present relatively close to each other. Wallace's Line is one of the many boundaries drawn by naturalists and biologists since the mid-1800s intended to delineate constraints on the distribution of the fauna and flora of the archipelago.
Historical context

One of the earliest descriptions of the biodiversity in the Indo-Australian Archipelago dates back to 1521 when Venetian explorer
Pigafetta recorded the biological contrasts between the Philippines and the
Maluku Islands
The Maluku Islands ( ; , ) or the Moluccas ( ; ) are an archipelago in the eastern part of Indonesia. Tectonics, Tectonically they are located on the Halmahera Plate within the Molucca Sea Collision Zone. Geographically they are located in West ...
(Spice Islands) (on opposite sides of Wallace's Line) during the continuation of the voyage of
Ferdinand Magellan
Ferdinand Magellan ( – 27 April 1521) was a Portuguese explorer best known for having planned and led the 1519–22 Spanish expedition to the East Indies. During this expedition, he also discovered the Strait of Magellan, allowing his fl ...
, after Magellan had been killed on
Mactan
Mactan is a densely populated island located a few kilometers (~1 mile) east of Cebu Island in the Philippines. The island is part of Cebu province and it is divided into the city of Lapu-Lapu and the municipality of Cordova.
The island is ...
. Later on, the English navigator
G. W. Earl published his observations in faunal differences between the islands in the Indo-Australian archipelago.
In 1845, G. W. Earl described how shallow seas connected islands on the west (
Sumatra
Sumatra () is one of the Sunda Islands of western Indonesia. It is the largest island that is fully within Indonesian territory, as well as the list of islands by area, sixth-largest island in the world at 482,286.55 km2 (182,812 mi. ...
,
Java
Java is one of the Greater Sunda Islands in Indonesia. It is bordered by the Indian Ocean to the south and the Java Sea (a part of Pacific Ocean) to the north. With a population of 156.9 million people (including Madura) in mid 2024, proje ...
, etc.) with the Asian continent and with similar wildlife, and islands on the east such as
New Guinea
New Guinea (; Hiri Motu: ''Niu Gini''; , fossilized , also known as Papua or historically ) is the List of islands by area, world's second-largest island, with an area of . Located in Melanesia in the southwestern Pacific Ocean, the island is ...
were connected to Australia and were characterized by the presence of
marsupial
Marsupials are a diverse group of mammals belonging to the infraclass Marsupialia. They are natively found in Australasia, Wallacea, and the Americas. One of marsupials' unique features is their reproductive strategy: the young are born in a r ...
s.
These early investigations assisted Wallace in developing his theories about the biogeography which he stated publicly in his 1859 paper after extensively traveling the region.
He proposed a line to the east of
Bali
Bali (English:; Balinese language, Balinese: ) is a Provinces of Indonesia, province of Indonesia and the westernmost of the Lesser Sunda Islands. East of Java and west of Lombok, the province includes the island of Bali and a few smaller o ...
since "all the islands eastward of
Borneo
Borneo () is the List of islands by area, third-largest island in the world, with an area of , and population of 23,053,723 (2020 national censuses). Situated at the geographic centre of Maritime Southeast Asia, it is one of the Greater Sunda ...
and
Java
Java is one of the Greater Sunda Islands in Indonesia. It is bordered by the Indian Ocean to the south and the Java Sea (a part of Pacific Ocean) to the north. With a population of 156.9 million people (including Madura) in mid 2024, proje ...
formed part of an Australian or Pacific continent, from which they were separated."
The proposal of the line, however, was not the main objective of Wallace's endeavours: His primary purpose was in fact to understand the geological phenomena and the colonization events that caused the boundaries in faunal distribution in the region through the development of his theories of evolution and biogeography.
Wallace's studies in
Indonesia
Indonesia, officially the Republic of Indonesia, is a country in Southeast Asia and Oceania, between the Indian Ocean, Indian and Pacific Ocean, Pacific oceans. Comprising over List of islands of Indonesia, 17,000 islands, including Sumatra, ...
demonstrated the emerging
theory of evolution
Evolution is the change in the heritable characteristics of biological populations over successive generations. It occurs when evolutionary processes such as natural selection and genetic drift act on genetic variation, resulting in certai ...
, at about the same time as
J. D. Hooker and
Asa Gray
Asa Gray (November 18, 1810 – January 30, 1888) is considered the most important American botany, botanist of the 19th century. His ''Darwiniana'' (1876) was considered an important explanation of how religion and science were not necessaril ...
published essays also supporting
Darwin's hypothesis. On the other hand, the lack of knowledge of
tectonic plate
Plate tectonics (, ) is the scientific theory that the Earth's lithosphere comprises a number of large tectonic plates, which have been slowly moving since 3–4 billion years ago. The model builds on the concept of , an idea developed durin ...
s, and the uncertainty about biodiversity in the
Philippines
The Philippines, officially the Republic of the Philippines, is an Archipelagic state, archipelagic country in Southeast Asia. Located in the western Pacific Ocean, it consists of List of islands of the Philippines, 7,641 islands, with a tot ...
, left Wallace with some contradicting points he had to deal with concerning his theory on biogeography.
In fact, Wallace did not include the Philippines in his 1859 paper, and the determination of a line in honor of his name was suggested by
T. H. Huxley
Thomas Henry Huxley (4 May 1825 – 29 June 1895) was an English biologist and anthropologist who specialized in comparative anatomy. He has become known as "Darwin's Bulldog" for his advocacy of Charles Darwin's theory of evolution.
The stor ...
(1868).
Huxley studied the distribution of
gallinaceous birds in the archipelago, and noticed that species in the Philippines were remarkably distinct from those in the Asiatic realm. Based on that, he redrew Wallace's boundary placing it to the west of the Philippines and named it "Wallace's Line", although Wallace himself had refused to include the Philippines on the east side of the line.
Because of the complexity of the geographical landscape and the differences in diversity of organisms around the archipelago, continuous attempts to characterize faunal and botanical boundaries were carried out after Wallace. Some of them are
*
Sclater line (1894)
*
Lydekker's line (1896)
*
Pelseneer's faunal balance (1904), also known as the
Weber line
Max Carl Wilhelm Weber van Bosse or Max Wilhelm Carl Weber (5 December 1852 – 7 February 1937) was a Germans, German-Dutch people, Dutch zoology, zoologist and biogeography, biogeographer.
Weber studied at the University of Bonn, then at t ...
*
Mayr
Mayr is a German surname. Notable people with the surname include:
* Andrea Mayr (born 1979), Austrian female long-distance runner
* Ernst Mayr (1904–2005), German American evolutionary biologist
* Franz Xaver Mayr (1875–1965), Austrian gastro ...
's faunal balance (1944)
In addition, several smaller transition sub-regional boundaries were also proposed.
More recent work assessing biodiversity assemblages, phylogeny, and using computer-based geospatial tools to analyze previous boundaries have led to patterns of division similar to those proposed through the 19th century, although some special cases not explained before are reinforced by these modern analyses.
[ ]
for instance, evaluated the distribution of land mammals, birds, and amphibians in Wallace's realms and concluded that the boundaries suggested by Wallace remain valid. Ali ''et al''. (2020), in a different attempt, studied the fauna of
Christmas Island
Christmas Island, officially the Territory of Christmas Island, is an States and territories of Australia#External territories, Australian external territory in the Indian Ocean comprising the island of the same name. It is about south o ...
and indicated that most of the ancestral colonizers of the island's land mammals and amphibians disappeared from the
Lombok Strait
The Lombok Strait () is a strait of the Bali Sea connecting to the Indian Ocean, and is located between the islands of Bali and Lombok in Indonesia. The Gili Islands are on the Lombok side.
Its narrowest point is at its southern opening, with a ...
. Therefore, they propose a re-conformation of Wallace's Line so that Christmas Island would be sited on the Australasian side of the biogeographical divide, instead of the oriental side.
Biogeography

Understanding of the
biogeography
Biogeography is the study of the species distribution, distribution of species and ecosystems in geography, geographic space and through evolutionary history of life, geological time. Organisms and biological community (ecology), communities o ...
of the region centers on the relationship of ancient
sea level
Mean sea level (MSL, often shortened to sea level) is an mean, average surface level of one or more among Earth's coastal Body of water, bodies of water from which heights such as elevation may be measured. The global MSL is a type of vertical ...
s to the
continental shelves
A continental shelf is a portion of a continent that is submerged under an area of relatively shallow water, known as a shelf sea. Much of these shelves were exposed by drops in sea level during glacial periods. The shelf surrounding an island ...
. Wallace's Line is visible geographically when the continental shelf contours are examined. It figures as a deep-water channel that separates the southeastern edge of the
Sunda Shelf
Geology, Geologically, the Sunda Shelf () is a south-eastern extension of the continental shelf of Mainland Southeast Asia. Major landmasses on the shelf include the Indonesia, Indonesian islands of Bali, Borneo, Java, Madura Island, Madura, an ...
from the
Sahul Shelf
Geology, Geologically, the Sahul Shelf () is a part of the continental shelf of the Australia (continent), Australian continent, lying off the northwest coast of mainland Australia.
Etymology
The name "Sahull" or "Sahoel" appeared on 17th c ...
. The Sunda Shelf links Borneo, Bali, Java, and Sumatra underwater to the mainland of southeastern Asia, while the Sahul Shelf connects Australia to New Guinea and their adjacent islands.
During the Pleistocene, when the
ocean levels were up to 120 metres (390 ft) lower, islands became connected, but never uniting Asia with Australia. Consequently, for over 50 million years, deep water between those two large continental shelf areas created a barrier that kept the flora and fauna of Australia separated from those of Asia. It can reasonably be concluded it was an ocean barrier preventing species migration because the physical aspects of the separated islands are very similar.
Thus, the ''
Wallacea
Wallacea is a biogeography, biogeographical designation for a group of mainly list of islands of Indonesia, Indonesian islands separated by deep-water straits from the Asian and Australia (continent), Australian continental shelf, continental ...
'' region consists of islands that remained isolated on their respective continental land masses, with only those organisms capable of crossing the straits between islands populating them.
Alternatively, "
Weber's line
Max Carl Wilhelm Weber van Bosse or Max Wilhelm Carl Weber (5 December 1852 – 7 February 1937) was a German- Dutch zoologist and biogeographer.
Weber studied at the University of Bonn, then at the Humboldt University in Berlin with the z ...
" runs through this transitional area (to the east of center), at the tipping point between Asian species against those with Australian origins.
Zoogeography
The distributions of many bird species follow the limits of the line, since many birds do not cross even the shortest stretches of open ocean water. Among mammals,
bat
Bats are flying mammals of the order Chiroptera (). With their forelimbs adapted as wings, they are the only mammals capable of true and sustained flight. Bats are more agile in flight than most birds, flying with their very long spread-out ...
s have distributions that can cross the line, but larger terrestrial mammals are generally limited to one side or the other. On the Australian side, many species of marsupials are present, and some monotremes, alongside native rodents—although the occurrence of rodents in this case is derived from more recent colonization events.
By contrast, to the Asian side, marsupials are excluded, and placental mammals such as apes, cats, elephants, monkeys, rhinoceroses, and other species are found.
Exceptions to this include
macaque
The macaques () constitute a genus (''Macaca'') of gregarious Old World monkeys of the subfamily Cercopithecinae. The 23 species of macaques inhabit ranges throughout Asia, North Africa, and Europe (in Gibraltar). Macaques are principally f ...
s, pigs, and
tarsier
Tarsiers ( ) are haplorhine primates of the family Tarsiidae, which is the lone extant family within the infraorder Tarsiiformes. Although the group was prehistorically more globally widespread, all of the existing species are restricted to M ...
s on Sulawesi.
Other groups of plants and animals show differing patterns, but the overall pattern is striking and reasonably consistent.
Flora
Flora (: floras or florae) is all the plant life present in a particular region or time, generally the naturally occurring (indigenous (ecology), indigenous) native plant, native plants. The corresponding term for animals is ''fauna'', and for f ...
do not follow the Wallace Line to the same extent as
fauna
Fauna (: faunae or faunas) is all of the animal life present in a particular region or time. The corresponding terms for plants and fungi are ''flora'' and '' funga'', respectively. Flora, fauna, funga and other forms of life are collectively ...
, since their colonization events differ in their ability to spread across bodies of water. One genus of plants that does not cross the line is the Australasian genus ''
Eucalyptus
''Eucalyptus'' () is a genus of more than 700 species of flowering plants in the family Myrtaceae. Most species of ''Eucalyptus'' are trees, often Mallee (habit), mallees, and a few are shrubs. Along with several other genera in the tribe Eucalyp ...
'', except for one species, ''
E. deglupta'', which naturally occurs on the island of
Mindanao
Mindanao ( ) is the List of islands of the Philippines, second-largest island in the Philippines, after Luzon, and List of islands by population, seventh-most populous island in the world. Located in the southern region of the archipelago, the ...
in the Philippines.
See also
*
Geography of Indonesia
Indonesia is an archipelagic country located in Southeast Asia and Oceania, lying between the Indian Ocean and the Pacific Ocean. It is located in a strategic location astride or along major sea lanes connecting East Asia, South Asia and Ocean ...
*
References
Sources
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Further reading
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External links
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{{Portal bar, Indonesia, Evolutionary biology, Geography
Biota of the Australasian realm
Biogeography
Celebes Sea
Ecoregions of Indonesia
Biota of the Indomalayan realm
Natural history of Indonesia
Regions of Southeast Asia
Wallacea