On the tendency of species to form varieties: and on the perpetuation of varieties and species by natural means of selection.

The first printed exposition of the “Darwinian” theory of evolution by natural selection. Had not Wallace independently discovered the theory of natural selection, it is possible that the extremely cautious Darwin might never have published his evolutionary theories during his lifetime. However, Wallace conceived the theory during an attack of malarial fever in Ternate in the Mollucas (February, 1858) and sent a manuscript summary to Darwin, who feared that his discovery would be pre-empted. In the interest of justice Joseph Dalton Hooker and Charles Lyell suggested joint publication of Wallace’s paper, On the tendency of varieties to depart indefinitely from the original type, prefaced by a section of a manuscript of a work on species written by Darwin in 1844, when it was read by Hooker, plus an abstract of a letter by Darwin to Asa Gray, dated 1857, to show that Darwin’s views on the subject had not changed between 1844 and 1857.

The Darwin-Wallace paper was issued in five different forms, all from the same setting of type. Four of these resulted from the publishing customs of the Linnean Society of London, which issued the journal in three different printed wrappers, depending on whether members subscribed to the zoological or botanical parts alone or both parts together. The fourth form was publication in the annual volume of the Journal, "made up from reserved stock of the parts with new title pages, dated in the year of completion of the volume, and indexes. This again was available complete or as Zoology or Botany alone" (Freeman). The fifth form was the authors' offprint. That form is of the greatest rarity.