Which naturalist independently developed a theory of natural selection in 1858?

Alfred Russel Wallace independently developed a theory of natural selection in 1858. His ideas closely matched Charles Darwin’s explanation of how species change over generations.

While working in the Malay Archipelago, Wallace wrote an essay describing natural selection and sent it to Darwin in 1858. Darwin had been developing similar ideas privately for many years but had not yet published them. Wallace’s letter prompted Darwin’s colleagues to arrange a joint presentation of their work to the Linnean Society of London.

The event helped establish priority for both men, although Darwin soon published the much larger and more detailed On the Origin of Species in 1859. Wallace continued to make major contributions to biology, geography, and biogeography, the study of how species are distributed across Earth.

Wallace is sometimes omitted from simplified accounts that present Darwin as the sole discoverer of natural selection. The fair canonical answer to this question is Alfred Russel Wallace, whose independent 1858 formulation is one of the most important examples of simultaneous scientific discovery.