"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 journal article, comprising and resulting from the 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The Tendency of Varieties to Depart Indefinitely from the Original Type by Alfred Russel Wallace and an Extract from an unpublished Work on Species from Charles Darwin's Essay of 1844. The article also includes an Abstract of a Letter from Darwin to Asa Gray, and an introductory letter by Joseph Dalton Hooker and Charles Lyell. The article was the first announcement of the Darwin–Wallace theory of evolution by natural selection; and 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. Events leading up to the publication 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. He wrote out his ideas in an 1842 "pencil sketch", then 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. Alfred Russel Wallace, a naturalist working in Borneo, had a paper on the "introduction" of species published in Annals and Magazine of Natural History. This made guarded comments about evolution, and in the spring of 1856 it was noticed by Lyell who drew it to the attention of Darwin who was