On the Road to the Origin with Darwin, Hooker, and Gray DUNCAN M. PORTER Department of Biology Virginia Polytechnic Institute and State University Blacksburg, Virginia 24061 INTRODUCTION I began this paper intending to write a short essay with the title "Plant Geography in The Origin of Species." However, I find that it has evolved into something quite different. Since the summer of 1989, when the original title was chosen, I have read some unpublished letters at the Royal Botanic Gardens, Kew, and the Gray Herbarium of Harvard University that led me to substitute the present title. Much of the present paper now consists of excerpts from letters between Charles Darwin (1809-1882), Asa Gray (1810-1888), and Joseph Dalton Hooker (1817-1911). They are relevant to my subject because Darwin depended upon Gray and Hooker, botanists respectively at Harvard and Kew, for much of the information on phytogeography in the Origin. I intend to pursue that theme in a later publication. I do not apologize for these long excerpts, as I think that the story is best told in the words of the protagonists. Also, they show that Darwin was not operating in a vacuum. Letters of Asa Gray was published in 1893 (J. Gray 1893), and Life and Letters of Sir Joseph Dalton Hooker in 1918 (L. Huxley 1918). In spite of the large numbers of letters contained in these four volumes, many of the letters that I quote from have never been published. Apparently, they were not deemed of sufficient interest to the general audience that was presumed to comprise the readers of such collections. Before they are explored, however, we must see where Gray and Hooker fit in the path leading to the publica- tion of On the Origin of Species (C. Darwin 1859). Thomas Henry Huxley (1825-1895) also enters our story, but more for what he is alleged to have done rather than for any early influence on Darwin. In spite of his son Leonard's statement that "Huxley was one of the few privileged to learn Darwin's argument before it was given to the world" (L. Huxley 1900:178), Journal of the History of Biology, vol. 26, no. 1 (Spring 1993), pp. 1-38. 1993 Kluwer Academic Publishers. Printed in the Netherlands. 2 DUNCAN M. PORTER T. H. Huxley knew of Darwin's interest in the origin of species, but he did not know about natural selection as an explanation until publication of the Origin (Di Gregorio 1984). Table 1 outlines a paper trail that culminates in the publication of the Origin. There are some observations on phytogeography in Darwin's notebooks kept on the 1831-1836 voyage of H.M.S. Beagle (Porter 1987). Likewise, in his postvoyage transmutation notebooks of 1836-1844 (C. Darwin 1987), Darwin records queries and comments on plant distribution, mainly engendered by his copious reading. In spite of this, there is not much discussion of evidence from plant geography to bolster Darwin's evolutionary arguments in his 1842 sketch and 1844 essay (de Beer 1958). We now know that the latter was offered to Joseph Hooker for his comments in 1845, but that Hooker did not read Darwin's essay until 1847 (Burkhardt and Smith 1988:11). As we shall see, Hooker was aware of Darwin's evolutionary hypothesis by 1844, but Darwin did not confide in Gray until 1857. The only one of our other players documented to have read the 1844 essay was Huxley, but he did not do so until about 1887 (E Darwin 1887, 1:375). Table 1. The path leading to the publication of On the Origin of Species Beagle Notebooks (1831-1836) Transmutation Notebooks (1836-1844) Sketch of 1842 Essay of 1844 Natural Selection (1856-1858) Darwin-Wallace "joint paper" (1858) On the Origin of Species (1859) Following Hooker's 1847 comments on the essay, Darwin's use of botanical evidence for his evolutionary ideas increased enor- mously, as can be seen in their copious correspondence (Burkhardt and Smith 1987, 1988, 1989, 1990, 1991). Indeed, by 1856-1858, when Darwin was working on his massive manuscript Natural Selection (C. Darwin 1975), Hooker had read and commented on several parts - most extensively on the last chapter, "Geographical Distribution." When Darwin received the fateful letter from Alfred Russel Wallace in June 1858 that revealed Wallace's ideas about the mech- anism of evolutionary change, after more than twenty years of gathering data he finally was writing out his own ideas for publi- On the Road to the Origin with Darwin, Hooker, and Gray 3 cation. Hooker and Sir Charles Lyell (1797-1875), Darwin's geological mentor, advised that the manuscript accompanying Wallace's letter be published immediately, along with proof that Darwin had formulated these ideas first. Thus was born the Darwin-Wallace "joint paper," presented to the Linnean Society of London on July 1, 1858, and published on August 30, 1858 (Darwin and Wallace 1858a). Part of the proffered proof that Darwin had priority in the matter was an abstract of an 1857 letter from Darwin to Gray, discussed below. The Origin, of course, was written as a result of Wallace's letter, Darwin first having tried and failed to produce thirty-page paper on his ideas for the Linnean Society. Darwin looked upon the Origin as an abstract of his "big book," Natural Selection. EARLY STEPS TOWARD TRANSMUTATION We now know that Hooker was not the only one with whom Darwin shared his evolutionary thoughts, nor was he the first (Table 2). Indeed, the first person who can be documented as knowing that Darwin was collecting information on the origin and variation of species was the geologist Charles Lyell, at the time his closest confidant. On September 15, 1838, Darwin wrote: I have lately been sadly tempted to be idle, that is as far as pure geology is concerned, by the delightful number of new views, which have been coming in, thickly & steadily, on the classification & affinities & instincts of animals - bearing on the question of species - note book, after note book has been filled, with facts, which begin to group themselves clearly under sublaws. (Burkhardt and Smith 1986:107) On June 15, 1838, he had written to his second cousin William Darwin Fox (1805-1880), who had introduced Darwin to the joys of entomology when they were students at Cambridge, that I am delighted to hear, you are such a good man, as not to have forgotten my questions about the crossing of animals. It is my prime hobby & I really think some day, I shall be able to do something on that most intricate subject species & varieties. (Burkhardt and Smith 1986:92) However, this is a much less clear statement of his intentions than that to Lyell. A less ambiguous statement was sent to Fox in January 1841: 4 DUNCAN M. PORTER Table 2. Darwin's associates and correspondents Name Variation a Transmutationb Charles Lyell 1838 1844? John Stevens Henslow 1839 William Darwin Fox 1841 1856 George Robert Waterhouse 1843 Leonard Jenyns 1843? 1844 Joseph Dalton Hooker 1844 1844 Leonard Homer 1844 or 1845 Charles James Fox Bunbury 1845 Richard Owen 1845 Ernst Dieffenbach 1847 Asa Gray 1855 1857 Hewett Cottrell Watson 1855? Edward Blyth 1855? Edgar Leopold Layard 1855 Charles Augustus Murray 1855 George Henry Kendrick Thwaites 1856 Syms Covington 1856 Thomas Henry Huxley 1856 John Lubbock 1856 Thomas Vernon Wollaston 1856 Laurence Edmondston 1856 Samuel Pickworth Woodward 1856 1856 John Edward Gray 1856 Frances Mackintosh Wedgwood 1856? Thomas Campbell Eyton 1856 Philip Henry Gosse 1856 James Dwight Dana 1856 1856 Hensleigh Wedgwood 1857 Alfred Russel Wallace 1857 George Bentham 1857 Jean Louis Armand de Quatrefages de Br6au 1858? Erasmus Alvey Darwin 1858 a Those who knew that Darwin was collecting information "on the origin and variation of species," and the documented dates that he introduced the subject to them. b Associates with whom Darwin shared his doubts on "species immutability," and the documented dates he first opened the subject. The dates have been determined primarily by information from Burkhardt and Smith (1986, 1987, 1988, 1989, 1990, 1991). On the Road to the Origin with Darwin, Hooker, and Gray 5 If you attend at all to Nat. His - I send you this P.S. as a memento, that I continue to collect all kinds of facts, about "Varieties & Species" for my some-day work to be so entitled - the smallest contributions, thankfully accepted. (Burkhardt and Smith 1986:279) In November 1839 Darwin wrote to his old Cambridge mentor John Stevens Henslow (1796-1861), Professor of Botany, that I keep on steadily collecting every sort of fact, which may throw light on the origin & variation of species (Burkhardt and Smith 1986:238) This implies, but does not prove, that Henslow was aware of Darwin's interest in the subject before he received this letter. The others whom we now know to have been aware of Darwin's interest were the British Museum zoologist George Robert Waterhouse (1810-1888), who described the mammals and some of the insects from the Beagle voyage, in 1843; Leonard Jenyns (1800-1893), author of the Beagle fishes and Henslow's brother- in-law, apparently in 1843; Joseph Dalton Hooker, botanist son of the director of the Royal Botanic Gardens, Kew, eventually to become Henslow's son-in-law, in 1844; Ernst Dieffenbach (1811-1855), a naturalist who in 1844 translated Darwin's Journal of Researches (C. Darwin 1839b) into German, in 1847; and Asa Gray, Fisher Professor of Natural History at Harvard University, not until 1855. From 1847 through 1854, Darwin's research and writing were almost entirely directed toward a systematic study of living and fossil barnacles (1851a, 1851b, 1854, 1854-58).