Wallace’s Expeditions Give Rise to Biogeography Summary

  • Last updated on November 10, 2022

Naturalist Alfred Russel Wallace developed a theory of evolution through natural selection similar to that of Charles Darwin. Through his explorations of the Malay archipelago, Wallace also discovered a major geographic discontinuity—later called Wallace’s line—between animals of Asian origin and those related to Australian forms. He thus initiated the modern discipline of biogeography, a cornerstone of ecology and conservation biology.

Summary of Event

Alfred Russel Wallace had little formal education but developed a keen interest in natural history as a young man. In 1848, he traveled to Brazil’s Amazon Amazon River basin to collect specimens of plants and animals to sell in his native Great Britain and to ponder what forces drive evolution. A growing acceptance of geologist Sir Charles Lyell’s Geology view that the earth was far older than had previously been believed allowed biologists of the day to consider whether, over long periods of time, species could evolve from preexisting species. No one had yet posited a convincing mechanism for evolutionary change, however. During his four years in the Amazon, Wallace did not solve the problem. Wallace, Alfred Russel Biogeography Evolution;and biogeography[Biogeography] Darwin, Charles [p]Darwin, Charles;and Alfred Russel Wallace[Wallace] [kw]Wallace’s Expeditions Give Rise to Biogeography (1854-1862) [kw]Expeditions Give Rise to Biogeography, Wallace’s (1854-1862) [kw]Give Rise to Biogeography, Wallace’s Expeditions (1854-1862) [kw]Biogeography, Wallace’s Expeditions Give Rise to (1854-1862) Wallace, Alfred Russel Biogeography Evolution;and biogeography[Biogeography] Darwin, Charles [p]Darwin, Charles;and Alfred Russel Wallace[Wallace] [g]Southeast Asia;1854-1862: Wallace’s Expeditions Give Rise to Biogeography[2970] [g]Indonesia;1854-1862: Wallace’s Expeditions Give Rise to Biogeography[2970] [g]Malaysia;1854-1862: Wallace’s Expeditions Give Rise to Biogeography[2970] [c]Genetics;1854-1862: Wallace’s Expeditions Give Rise to Biogeography[2970] [c]Biology;1854-1862: Wallace’s Expeditions Give Rise to Biogeography[2970] [c]Geography;1854-1862: Wallace’s Expeditions Give Rise to Biogeography[2970] [c]Exploration and discovery;1854-1862: Wallace’s Expeditions Give Rise to Biogeography[2970] Malthus, Thomas Robert Lyell, Sir Charles

Early in 1854, in a second attempt to generate income and to consider further the origin of species, Wallace sailed to the Malay archipelago Malay archipelago (now Indonesia and Malaysia). This chain of islands, which stretches 4,000 miles east to west, and 1,300 miles north to south across the equator, attracted Wallace because of its species diversity. In his eight years there, he undertook about seventy expeditions, traveling approximately 14,000 miles. He gathered 126,000 specimens, including more than 1,000 new to Western science.

Wallace’s Malay observations led him to write more than forty scientific papers. One of his major discoveries was a faunal discontinuity within the archipelago. Later dubbed Wallace’s line, this narrow belt of sea constituted a zoogeographic boundary between the eastern extent of many Asian animal forms and the western extent of many Australian forms. The line separated the relatively small islands of Bali and Lombok, which are less than fifteen miles apart. To the north of these islands, the line ran between the much larger islands, Borneo and Celebes (now Sulawesi).

Although the Wallace line is not a precise demarcation, it is helpful as a rough separation. The Asian realm has a rich array of placental mammals, including tigers, elephants, and many kinds of squirrels, as well as many birds such as woodpeckers, pheasant, babblers, and bulbuls. The Australian Australia;fauna of region, in contrast, boasts egg-laying mammals (monotremes) such as the platypus; a wide assortment of marsupial mammals, including the kangaroo; and birds that include cockatoos and birds of paradise. The Australian region is poor in primates (other than humans), whereas the Asian region boasts monkeys, gibbons, and orangutans. Freshwater fish are much more abundant and diverse in the Asian region than they are in the Australian region.

Wallace reasoned, correctly, that this discontinuity was related to the appearance and disappearance, over geological time, of land bridges between the Asian mainland and the islands on the Asian side of the line, and, similarly, bridges between Australia and some of the islands on the other side of the line. Wallace’s line, however, marks a deep, perpetual strait, which most animals could not cross.

Wallace made a discovery far more significant than the line, however. The first glimmerings of his breakthrough are outlined in an essay he wrote in Sarawak, Borneo, called “On the Law Which Has Regulated the Introduction of New Species” (1855). By strongly arguing that organisms must have evolved from earlier forms, he came closer than anyone else up to that time in describing the unfolding of evolution. Published later that year in England, the paper caused little stir because it posited no mechanism for evolution, but it did come to the attention of Charles Darwin, who was considering the problem of a mechanism for evolution.

In February, 1858, during an attack of malaria in the Moluccas Malaria;in Molucca Islands[Molucca Islands] (now Maluku), Wallace had a burst of insight. He realized, as had Darwin much earlier, that the concept of limits to human population growth imposed by the availability of resources—an idea put forth by Thomas Robert Malthus Malthus, Thomas Robert Essay on the Principle of Population, An (Malthus) in his 1798 work An Essay on the Principle of Population—was relevant to the origin of species. He conceived the theory of evolution by natural selection: Competition for limited resources generates new species from preexisting ones through the differential survival of individuals having beneficial variations. Those individuals that are best adapted to their surroundings have the greatest chance of surviving to pass along their traits to their progeny. For years Darwin had been quietly accumulating data to support a remarkably similar theory. Both Wallace and Darwin had been schooled in an archipelago (Darwin in the Galapagos Galapagos Islands Islands, off the coast of Ecuador), where they had observed that a species on one island is often matched by closely similar species on nearby islands.

Soon after his illness, Wallace wrote “On the Tendency of Varieties to Depart Indefinitely from the Original Type” (1858). He sent the manuscript to Darwin, whose close friends arranged for the Linnaean Society of Dublin to publish Wallace’s essay jointly with two of Darwin’s earlier, private writings that outlined his very similar theory. The three items were read to the society at its meeting on July 1, 1858. Wallace’s paper prompted Darwin to Darwin, Charles [p]Darwin, Charles;On the Origin of Species publish his own, fuller account one year later, as On the Origin of Species On the Origin of Species (Darwin) (1859).

In 1862, Wallace returned to England, where he was known as the greatest living authority on the Malay archipelago Malay archipelago . His well-received book, The Malay Archipelago: The Land of the Orang-Utan and the Bird of Paradise—A Narrative of Travel, with Studies of Man and Nature (1869), based on his eight years in the region, acquainted many Europeans with a realm they had known but dimly. During Wallace’s lifetime, the book was reprinted fifteen times in England and translated around the world. His vast insect collections from the archipelago are now held mostly by Oxford University and the British Natural History Museum Museums;natural history .

Wallace remained a staunch evolutionist in all respects but one. Although he had at first held that human evolution could be explained by natural selection Darwin, Charles [p]Darwin, Charles;on natural selection[Natural selection] , a view that Darwin set forth in The Descent of Man, and Selection in Relation to Sex Darwin, Charles [p]Darwin, Charles;The Descent of Man[Descent of Man] Descent of Man, The (Darwin) (1871), Wallace later rejected Darwin’s naturalistic views about human origins. Wallace became persuaded that an overruling intelligence created humans by endowing apes with enlightened minds. This spiritualism of his later years somewhat clouded his scientific reputation.


Although eclipsed by Darwin, Wallace is still accorded a measure of credit for the theory of evolution by natural selection, and he is ranked as a first-rate scientist of his time. His Malay research was important in establishing the geographical ranges of many species, and he helped pave the way for biologists—including Wallace himself—to divide the world into six major zoogeographic regions.

Not until more than a century after Wallace’s Malay archipelago research, however, when the field of plate tectonics developed, was Wallace’s line more fully understood and accepted. During the 1970’s, scientists came to learn that, millions of years ago, the movement of continental plates had brought the Asian and Australian plates, each having its separate and independently evolved flora and fauna, into semijuxtaposition along Wallace’s line. Scientists have now concluded that the land bridges were caused by decreases in sea level during the ice ages of the Pleistocene Epoch (from about 2 million years to 18,000 years ago).

Scientists now know that the islands of Celebes and the Moluccas, located in the deep seas between the Asian and Australian continental shelves, were never connected to either continent by land bridges. These islands, which are somewhat biologically impoverished because of their long isolation, are known as Wallacea, in honor of Wallace.

Further Reading
  • citation-type="booksimple"

    xlink:type="simple">Brackman, Arnold C. A Delicate Arrangement: The Strange Case of Charles Darwin and Alfred Russel Wallace. New York: Times Books, 1980. Brackman argues that Darwin and his friends conspired to deny Wallace credit for having first discovered the theory of biological evolution.
  • citation-type="booksimple"

    xlink:type="simple">Daws, Gavan, and Marty Fujita. Archipelago: The Islands of Indonesia, from the Nineteenth Century Discoveries of Alfred Russel Wallace to the Fate of Forests and Reefs in the Twenty-First Century. Berkeley: University of California Press, 1999. A richly illustrated narrative of Wallace’s journey and his insight into evolution. Describes Indonesia’s natural world and present environmental degradation.
  • citation-type="booksimple"

    xlink:type="simple">Diamond, Jared. “Mr. Wallace’s Line (Biogeographic Division Between Oriental and Australian Regions).” Discover 18 (1997): 76-83. Discusses the rich biological differences among the species separated by Wallace’s line.
  • citation-type="booksimple"

    xlink:type="simple">Fichman, Martin. An Elusive Victorian: The Evolution of Alfred Russel Wallace. Chicago: University of Chicago Press, 2004. An analytical look at Wallace’s intellectual and cultural views in the context of Victorian England.
  • citation-type="booksimple"

    xlink:type="simple">Larson, Edward J. Evolution: The Remarkable History of a Scientific Theory. New York: Modern Library, 2004. A lucid and broad overview of the theory of evolution that includes Wallace’s contributions to the science.
  • citation-type="booksimple"

    xlink:type="simple">Slotten, Ross. The Heretic in Darwin’s Court: The Life of Alfred Russel Wallace. New York: Columbia University Press, 2004. A vivid, highly detailed, chronologically arranged biography that focuses on Wallace’s work in the shadow of the more famous Darwin.
  • citation-type="booksimple"

    xlink:type="simple">Van Osterzee, Penny. Where Worlds Collide: The Wallace Line. Ithaca, N.Y.: Cornell University Press, 1997. Covers Wallace’s discovery of the line named for him, how the line formed, and its meaning in the context of evolution.
  • citation-type="booksimple"

    xlink:type="simple">Wallace, Alfred Russel. The Alfred Russel Wallace Reader: A Selection of Writings from the Field. Edited by Jane R. Camerini. Baltimore: Johns Hopkins University Press, 2002. A foreword by naturalist and writer David Quammen opens this collection of Wallace’s writings, including his “On the Tendency of Varieties to Depart Indefinitely from the Original Type.” Includes a biographical essay by the editor.
  • citation-type="booksimple"

    xlink:type="simple">_______. The Malay Archipelago. A Narrative of Travel with Studies of Man and Nature. 1869. Reprint. Hong Kong: Periplus, 2000. Wallace’s popular, significant account of his explorations in Indonesia and Malaysia.

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