On the Tendency of Species to form Varieties; and on the Perpetuation of Varieties and Species by Natural Means of Selection

On the Tendency of Species to form Varieties; and on the Perpetuation of Varieties and Species by Natural Means of Selection is the title of a joint presentation of two scientific papers to the Linnean Society of London on 1 July 1858; On The Tendency of Varieties to Depart Indefinitely from the Original Type by Alfred Russel Wallace and an Extract from an unpublished Work on Species from Charles Darwin's Essay of 1844, together with an Abstract of a Letter from Darwin to Asa Gray. This was the first announcement of the Darwin – Wallace theory of evolution by natural selection; the papers appeared in print on 20 August 1858. The presentation of the papers spurred Darwin to write a condensed "abstract" of his "big book" on Natural Selection. This was published in November 1859 as On the Origin of Species.

On the voyage of the Beagle the young Charles Darwin took a break between graduating and starting his career as a clergyman to study the natural history of South America, an interest he had developed at the University of Edinburgh and the University of Cambridge. Influenced by Charles Lyell's Principles of Geology, he became an able geologist as well as collecting plant and animal specimens, and fossils of gigantic extinct mammals. By the return journey, he was connecting patterns of geographical and historical distribution, and starting to doubt the stability of Species. In September 1838 he conceived his theory of natural selection as the cause of evolution, then as well as developing his career as a geologist and writer worked privately on finding evidence and answering possible objections, and set out his ideas in an essay written in 1844. He discussed transmutation with his friend Joseph Dalton Hooker, who read the essay in 1847. After turning his attention to biology and completing eight years of work on barnacles, Darwin intensified work on his theory of species in 1854.

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