The prevailing view in British scientific and theological communities when Charles Darwin began his inquiries was that species were fixed, immutable types, created by God. The complex and intricate design of organisms was taken as evidence of creation by a Designer. William Paley, a natural theologian, developed the argument, which Darwin studied during his education at Cambridge.
However, the idea that species are not immutable but can be transmuted had many advocates before Darwin. They can be found as far back as the pre-Socratics, but the view was greatly advanced in early nineteenth century scientific discussions by Jean-Baptiste-Pierre-Antoine de Monet de Lamarck in his Philosophie zoologique: Ou, Exposition des considérations relative à l’histoire naturelle des animaux (1809; Zoological Philosophy: An Exposition with Regard to the Natural History of Animals, 1914). What Lamarck and other early evolutionary theorists lacked was an adequate mechanism to explain how evolution occurred.
Charles Lyell, in his Principles of Geology (1830-1833), argued that geological formations had been shaped by the same physical forces that acted on them today, a doctrine known as uniformitarianism. Although Lyell was not a transmutationist until after On the Origin of Species by Means of Natural Selection, he did acknowledge in the volumes that Darwin read that changing environments could lead species to undergo accommodations, migrations, and extinctions.