The British naturalist and explorer Alfred Russel Wallace independently developed a theory of evolution virtually identical to Charles Darwin’s. Both men, working on separate continents, arrived at the mechanism of evolutionary change driven by natural selection. This shared discovery in the mid-19th century profoundly reshaped the scientific understanding of life on Earth. Wallace’s deep commitment to fieldwork and his sharp analytical mind led to a realization that permanently linked his name with one of the most transformative ideas in biology.
Wallace’s Independent Discovery
Wallace’s quest to understand how new species arise began with his eight-year expedition to the Malay Archipelago, starting in 1854. His extensive travels throughout the islands, now parts of Malaysia and Indonesia, involved collecting over 125,000 specimens. This immense fieldwork provided him with evidence of persistent variation within species across different geographical ranges. His earlier 1855 paper, the “Sarawak Law,” proposed that every new species must arise near a closely allied pre-existing species, establishing a framework for his later breakthrough.
The critical insight struck Wallace in February 1858 while he was suffering from malarial fever on the island of Halmahera. Confined to his hut, he contemplated the enormous reproductive capacity of animal populations. He recalled Thomas Malthus’s Essay on the Principle of Population, which described the struggle for existence. Wallace realized that the constant overproduction of offspring meant that only those individuals best equipped to survive environmental pressures would live to reproduce.
This process of selective survival filtered out less-fit varieties, ensuring that advantageous traits were passed down to the next generation. Wallace grasped that this mechanism, acting over geological time, would inevitably cause species to diverge indefinitely from their original type. Within three days, he wrote out his entire theory, formally titled On the Tendency of Varieties to Depart Indefinitely from the Original Type. He sent the manuscript, known as the “Ternate Essay,” to Charles Darwin, a respected senior naturalist with whom he had corresponded.
The 1858 Joint Announcement
Darwin received Wallace’s manuscript at his home in Kent on June 18, 1858, a moment he described as being “forestalled.” He saw immediately that Wallace’s concise essay perfectly encapsulated the theory he had been developing for twenty years. Though Darwin had meticulously accumulated a mountain of evidence, he had not yet published a comprehensive word on natural selection. The arrival of the Ternate Essay presented a difficult dilemma concerning the priority of discovery.
Darwin turned to his influential colleagues, geologist Charles Lyell and botanist Joseph Dalton Hooker, for advice. Recognizing the similarity and importance of the two men’s independent work, Lyell and Hooker devised a plan to present both theories simultaneously. They combined Wallace’s complete essay with two unpublished excerpts from Darwin’s writings: a draft essay from 1844 and a letter to Asa Gray from 1857. This action ensured that both naturalists received credit for the co-discovery of natural selection.
The joint papers were read at the Linnean Society of London on July 1, 1858, marking the first public presentation of the theory of evolution by natural selection. The reading, titled On the Tendency of Species to form Varieties; and on the Perpetuation of Varieties and Species by Natural Means of Selection, established the unified concept. This event spurred Darwin to abandon his massive treatise and instead write an “abstract” of his work, which became the groundbreaking book On the Origin of Species, published in November 1859.
Alfred Russel Wallace’s Enduring Legacy
After the joint announcement, Wallace continued his extensive fieldwork in the Malay Archipelago until 1862, making him one of the most experienced field naturalists of his time. His observation of animal distribution led him to identify a sharp faunal boundary between the islands of Borneo and Sulawesi. This barrier, now known as the Wallace Line, separates Asian fauna to the west from the Australasian fauna to the east, providing a foundational concept for biogeography.
Wallace’s later philosophical views began to diverge from Darwin’s materialistic interpretation of natural selection. He argued that natural selection alone could not account for the development of the human brain, consciousness, and moral sense. He posited that some non-material or spiritual element must have guided human evolution beyond the physical process.
Beyond his scientific contributions, Wallace was a prominent social activist and humanitarian who championed land nationalization and women’s suffrage. He became a public figure known for taking controversial stances on social and political issues. Wallace remained Darwin’s most loyal public defender, frequently referring to the theory as “Darwinism.” His wide-ranging work in ecology, zoology, and social reform secures his distinct position as the co-founder of the theory and a major Victorian intellectual.