Darwin, “On the Tendency”
In this 1858 issue of the Journal of the Proceedings of the Linnaean Society (London), a seven-page summary of Darwin’s theory of evolution was published simultaneously with a short essay by Alfred Russel Wallace, who had come up with a very similar explanation of evolution. Darwin’s friend Charles Lyell made it clear in his introduction to the two articles that Darwin’s theory had been worked out before that of Wallace.
Charles Darwin (1809–1882). “On the Tendency of Species to Form Varieties...,” Journal of the Proceedings of the Linnaean Society. Vol. 3. London: Longman, Brown, 1858.