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.
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
Early in 1854, in a second attempt to generate income and to consider further the origin of species, Wallace sailed to the Malay archipelago
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
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
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
In 1862, Wallace returned to England, where he was known as the greatest living authority on the Malay archipelago
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
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.
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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. -
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. -
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. -
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. -
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. -
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. -
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. -
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. -
_______. 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.
Lambton Begins Trigonometrical Survey of India
Lamarck Publishes Zoological Philosophy
Scientists Study Remains of Giant Moas
Lyell Publishes Principles of Geology
Darwin Publishes On the Origin of Species
Archaeopteryx Lithographica Is Discovered
Mendel Proposes Laws of Heredity
Lartet Discovers the First Cro-Magnon Remains
Darwin Publishes The Descent of Man
Przhevalsky Explores Central Asia
Galton Defines “Eugenics”
Louis Agassiz; Karl Ernst von Baer; Samuel Butler; Georges Cuvier; Charles Darwin; Asa Gray; Ernst Haeckel; Thomas Henry Huxley; Sir Charles Lyell; Herbert Spencer.