On 18th June 1858, if his own account of events is to be believed (which has been unfairly questioned by some), Charles Darwin received the biggest bombshell of his scientific career. Having been working on his theory of evolution by means of Natural Selection for about 20 years, he received a letter from Alfred Russel Wallace, who was in Ternate on the Malayan Archipelago (modern day Indonesia). Wallace had independently come up with the theory of Natural Selection. Darwin was in danger of being scooped!
Wallace's letter no longer survives (which is wonderful for conspiracy theorists), but we do still have the letter Darwin immediately wrote to his friend and confidante, Charles Lyell:
My dear Lyell
Some year or so ago, you recommended me to read a paper by Wallace in the Annals, which had interested you & as I was writing to him, I knew this would please him much, so I told him. He has to day sent me the enclosed & asked me to forward it to you. It seems to me well worth reading. Your words have come true with a vengeance that I shd be forestalled. You said this when I explained to you here very briefly my views of "Natural Selection" depending on the Struggle for existence.— I never saw a more striking coincidence. if Wallace had my M.S. sketch written out in 1842 he could not have made a better short abstract! Even his terms now stand as Heads of my Chapters.