On 1 July 1858, a joint paper by Charles Darwin and Alfred Russel Wallace presenting their independently developed but remarkably similar ideas on evolution by natural selection was made public for the first time before the Linnean Society in London. The presentation was made by Darwin's friends J.D. Hooker and Sir Charles Lyell. Neither Darwin nor Wallace was present during the session. Read more about this historical event here.
I do not know if you have seen the wonderful book of Mr Darwin's "The Origin of Species" published about four years ago, which has revolutionised Natural History & caused more discussion & excitement than any other book <.....> on a scientific subject during the present century, I have some little share in the work myself having discovered the main principle on which the work depends, called by Mr. D. Natural Selection, & communicated it to him before the work was published.
Letter from A.R. Wallace to his brother John, dated January 2nd 1863. Transcript here.