This person sent charles darwin a copy of his theory which was essentially the same as darwin's theory of natural selection, proposing that new species are descendants of older species which have changed in response to environmental pressures.

Another person was also working with the same theory with Darwin, and he is Alfred Russel Wallace. His paper is entitled "On the tendency of Varieties to Depart Indefinitely from the Original Type". This then prompted Darwin to finish his theory and submit his paper to the Linnean Society of London.