On September 5 in 1857, from his country home in Down, England, 48-year-old Charles Darwin reveals the theory of evolution in a letter to Harvard botanist Asa Gray. The enthusiastic reaction of Gray and others, and the knowledge that Alfred Russel Wallace has independently hit on the same theory, convince Darwin that it is finally time to publish his theory after 20 years of indecision.
—from The Illustrated Almanac of Science, Technology, and Invention