In 1847, Henry Walter Bates and Alfred Russel Wallace agreed to fund a scientific trip to the Amazon by collecting and selling natural history specimens. Their goal was also to gather evidence relevant to the “origin of species” question that was increasingly debated in natural history. This decision set the purpose and practical model for their expedition.
Bates and Wallace sailed from Liverpool in April 1848 and reached Pará (now Belém) by late May. They began collecting and preparing specimens soon after arrival, using the city as an initial base. This marked the start of Bates’s nearly eleven-year period of fieldwork in Amazonia.
After about a year of joint work near Pará, Bates and Wallace decided to separate to cover more territory and reduce overlap in collections. Bates shifted his travels deeper into the Amazon basin, moving among multiple river towns and collecting sites. This change expanded the geographic range and scientific value of their specimen gathering.
Bates eventually made Ega (Tefé), on the upper Amazon/Solimões, his headquarters for about four and a half years. From this base he worked surrounding waterways and forests, building extensive insect collections and detailed field notes. The long stay supported careful observation of species and local ecological patterns, not just rapid collecting.
In August 1852, Wallace’s ship caught fire and sank during his return trip, destroying the specimens he had with him. The loss became a well-documented example of how fragile scientific collections were during long-distance travel. Bates responded by sending his own collections on multiple ships to reduce the risk of a single catastrophic loss.
Through the 1850s, Bates continued extended trips in the upper Amazon system while maintaining a base in the Solimões region. This work combined collecting with close observation of behavior, habitats, and relationships among organisms. His long-term approach helped him notice patterns—such as striking resemblances among unrelated butterflies—that later became central to his scientific arguments.
By early 1859, Bates’s health had worsened after years in tropical conditions. On 11 February 1859, he left Ega (Tefé) and began the journey back downriver toward Pará and then onward to England. His departure marked the practical end of his continuous Amazon fieldwork.
Bates returned to England in 1859 after nearly eleven years in Amazonia, bringing a very large collection of specimens, mainly insects. The Linnean Society later summarized that he had sent back over 14,000 specimens, with more than half newly recorded species. This collection provided the material basis for his later scientific publications and identifications.
On 21 November 1861, Bates read a major paper to the Linnean Society based on his Amazon butterfly studies. He argued that some harmless species can gain protection by evolving to resemble unpalatable or dangerous species that predators avoid—an idea that later became known as Batesian mimicry. The paper helped connect detailed field observations to the emerging theory of evolution by natural selection.
In 1862, Bates’s detailed study of Heliconiidae butterflies in the Amazon was published in the Transactions of the Linnean Society of London. The work provided extensive evidence for mimicry and used Amazon examples to explain how natural selection could shape appearance across species. Publication made his argument broadly available to other scientists and became a classic reference in evolutionary biology.
In 1863, Bates published The Naturalist on the River Amazons with John Murray in London, turning his field experiences into an accessible narrative and scientific record. The book combined travel, observations of people and places, and natural history, while also supporting evolutionary explanations. It helped establish the Amazon expedition as a major episode in 19th-century naturalist exploration.
Bates’s book reported that his Amazon collections included 14,712 species, with over 8,000 described as new to science. This summary was noted in the Darwin Correspondence Project’s documentation of the period, reflecting how seriously leading scientists took Bates’s evidence. The scale of collecting underscored why long field expeditions mattered for expanding knowledge of biodiversity and supporting evolutionary research.
In early 1864, Bates was appointed assistant secretary of the Royal Geographical Society, a role he held for decades. The position gave him a stable base in the scientific world and connected him to exploration networks, publishing, and administration. This career step marked the expedition’s longer-term outcome: field experience converted into institutional influence and continuing scientific work.
Henry Walter Bates's Amazon expedition (1848–1859)