In these papers, read on July 1, 1858, Darwin's share amounts to little more than six pages, yet within this space he describes the geometrical rate of increase of animals, the checks that occur, the effects of changed conditions, the natural selection of the better equipped forms resulting from the struggle for existence, and the influence of sexual selection. Wallace insists on essentially the same view, which he calls that of progression and continued divergence. "This progression, by minute steps, in various directions, but always checked and balanced by the necessary conditions, subject to which alone existence can be preserved, may, it is believed, be followed out so as to agree with all the phenomena presented by organised beings, their extinction and succession in past ages, and all the extraordinary modifications of form, instinct, and habits which they exhibit." Those who read Wallace's original essay can best appreciate the extraordinary simplicity and nobility of character which inclined the elder naturalist, who had so long held the same views, to step aside in favour of the younger man, who from different researches was led to such similar conclusions. It may here be added that Hooker, in the Introductory Essay to the "Flora Tasmaniæ," dated November 4, 1859, before the publication of the "Origin of Species," but after seeing much of it in manuscript, accepted and advocated the view that species are derivative and mutable, and developed it as regards the geographical distribution of plants. FOOTNOTES: [6: It is worth while to reproduce here a few sentences from Erasmus Darwin's "Zoonomia," showing how acutely he guessed in the direction of evolution.