The first person to discover and publish the principle of
evolution by
natural selection, seven years before
Darwin began working on it, and thirty years before the publication of the
Origin of Species.
He did not fully develop the idea, which he threw out incidentally in a very obscure publication, and was not right in the details or consequences. Nevertheless Darwin gave him credit as soon as he found out.
Patrick Matthew, born 20 October 1790, died 8 June 1874, was a Scottish orchardist who in 1831 published a book On Naval Timber and Arboriculture on the best methods of raising trees for shipbuilding. In an appendix he speculated how continued weeding-out of less hardy individual trees could led to differences so great as to be different species: that is, the principle of natural selection.
He also anticipated the idea of punctuated equilibrium, in that he believed in catastrophist geology, and believed that evolution would be retarded in the periods between catastrophes. And he applied his ideas to humans in political writings: in effect, if the British settled all over the world, then the resulting Australians and New Zealanders would be the pick of the bunch.
Moving right along, once Darwin and Wallace's theory was made public and became famous in 1859, Matthew realized the significance of what he himself had written, and publicized it in an article in the Gardeners' Chronicle in April 1860, where Darwin read it and drew attention to it in a letter to Charles Lyell saying Matthew had "briefly but completely" anticipated him. He gives extensive credit to Matthew in the Origin (1861).
Matthew nevertheless considered himself unrecognized; he had "Discoverer of the Principle of Natural Selection" printed on his cards. He corresponded with Darwin.
To the end he believed in creationism, that is that there was a planned design in the beauty of nature; though natural selection accounted for some variation and creation of new species, it did not account for the entirety of nature, as Darwin came to believe. For this reason we cannot take the credit away from Darwin, who far more than Matthew or Wallace realized the full implications of their discovery.