On This Day August 20

Charles Darwin originally conceived his scientific theory of evolution by means of natural selection after being puzzled by the geographical distribution of wildlife and fossils he collected on the during his five-year voyage on the H.M.S. Beagle. He first published his theory on August 20, 1858 in The Journal of the Proceedings of the Linnean Society of London, alongside Alfred Russel Wallace's same theory. The next year Darwin expanded on his ideas in his book On the Origin of Species. 

Darwin's "B" notebook on Transmutation of Species

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