The Transmutation of species and transformism are 18th and early 19th-century ideas about the change of one species into another that preceded Charles Darwin's theory of evolution through natural selection. The French Transformisme was a term used by Jean Baptiste Lamarck in 1809 for his theory, and other 18th and 19th century proponents of pre-Darwinian evolutionary ideas included Denis Diderot, Étienne Geoffroy Saint-Hilaire, Erasmus Darwin, Robert Grant, and Robert Chambers, the anonymous author of the book Vestiges of the Natural History of Creation. Such ideas were associated with 18th century ideas of Deism and human progress. Opposition in the scientific community to these early theories of evolution, led by influential scientists like the anatomists Georges Cuvier and Richard Owen, and the geologist Charles Lyell, was intense. The debate over them was an important stage in the history of evolutionary thought and influenced the subsequent reaction to Darwin's theory.

The immediate reactions, from November 1859 to April 1861, to On the Origin of Species, the book in which Charles Darwin described evolution by natural selection, included international debate, though the heat of controversy was less than that over earlier works such as Vestiges of Creation. Darwin monitored the debate closely, cheering on Thomas Henry Huxley's battles with Richard Owen to remove clerical domination of the scientific establishment. While Darwin's illness kept him away from the public debates, he read eagerly about them and mustered support through correspondence.