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The Tendency of Varieties to Depart Indefinitely from the Original Type by Alfred Russel Wallace and an Extract from an unpublished Work on Species from Charles Darwin's Essay of 1844, together with an Abstract of a Letter from Darwin to Asa Gray.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 publication of the Darwin – Wallace theory of evolution by natural selection. Darwin was spurred to write a condensed "abstract" of his "big book" on Natural Selection, which was published in November 1859 as On the Origin of Species.