The concept of evolution by "survival of the fittest" was arrived at independently by both Darwin and Alfred Russel Wallace.
Wallace wrote to Darwin expounding his version of the theory in 1858. Wallace's conclusions were drawn after a study of species on the Indonesian island system of Aru, just as Darwin's had been during his visit to the Galapagos.
It is believed by some, though impossible to prove, that Darwin concealed the letter until his own version had been made public. What is beyond doubt is that the two were in regular communication. Papers introducing the theory of evolution were written by both Darwin and Wallace and presented at the same meeting of the Linnaean Society on 1 July 1858.
It is unjust that Darwin is lionised - religious fundamentalists aside - while Wallace moulders in obscurity.