Fifteen years before On the Origin of Species would appear in print (1859), Darwin penned a now famous letter to Joseph Hooker, eminent botanist and later Director of the Royal Botanic Gardens, Kew (1865-85). In this letter (January 11, 1844) to his friend, colleague, and confidant, Darwin first shared his thoughts on the mutability of species – “I think I have found out (here’s presumption!) the simple way by which species become exquisitely adapted to various ends” – likening it to “confessing a murder.” From this point on, Hooker became one of Darwin’s most important correspondents, ultimately playing a central role in the dissemination of Darwin’s (and Alfred Russel Wallace’s) theory of descent with modification through natural selection. He, with Charles Lyell, orchestrated the joint communication of Darwin’s and Wallace’s papers to the Linnean Society in 1858 – the first public announcement of the theory of natural selection.
As a prominent 19th century scientist, Hooker clearly understood the import and significance of these ideas, and he became the first published author to advocate Darwin’s and Wallace’s ideas in a remarkable, but today little known essay, the “Introductory Essay to the Flora of Tasmania”. This essay, completed in November, 1859, the same month as Origin, and published the following month, constitutes the first post-Origin era piece of independent scholarship on the processes and patterns of evolution. In 1861, Darwin would write of this essay that Hooker “admits the truth of the descent and modification of species, and supports this doctrine by many original observations.” The botanist F.O. Bower affirmed the originality of Hooker’s contributions in a memorial address delivered the year after Hooker’s death (and reprinted in the University of Chicago’s Botanical Gazette in 1913). Bower argued that “this publication of his belief was not merely an echo of assent to Darwin’s own opinions. It was a reasoned statement, advanced upon the basis of his own ‘self-thought,’ and his own wide systematic and geographical experience. From these sources he drew for himself support for the ‘hypothesis that species are derivative and mutable’” (388).
In many ways, the intellectual journey of Joseph Dalton Hooker in the 1840s and 1850s epitomizes these transformative decades in Great Britain leading up to the publication of On the Origin of Species. Hooker’s publications during this period reveal a man initially skeptical of species immutability, yet seeking the kinds of evidence and proof that might bring rational insight to bear on the question of how species are created.
Read more about Hooker’s contribution to evolutionary thought. [expand]
Hooker’s gradual conversion to evolutionism was informed not only by his rich correspondence with Darwin, but also by his own extensive analysis of botanical species and their distribution, critical reading on theories of evolution, and no little amount of intellectual sparring and collaboration with Darwin. During the early critical years when Darwin was formulating his theory, Hooker was working on a massive compilation of the floras of Antarctica, New Zealand, and Tasmania (Botany of the Antarctic Voyage– published 1844-1860) – a result of his field work between 1839 and 1843, when he served as assistant surgeon on the British Antarctic Expedition. The letters exchanged between the two naturalists from 1844 to 1859 are bursting with botanical species to genera ratios, questions of peculiar insular flora, and musings on floral species migration and geographic distribution.
As early as 1844, Hooker wrote to solicit Darwin’s advice, albeit somewhat sardonically, on “what writings on the subject of original creation will give me the best notion of the (mad) theories of some men from Lamarck’s twaddle upwards.” Yet, in his 1853 Introductory Essay to the Flora of New Zealand, Hooker hedges the species question, protesting his “inability to grapple with these great questions” and writing in the chapter “On the Limits of Species; Their Dispersion and Variation:” “It is no part of my present object to discuss the theoretical views that have been entertained on these obscure subjects” (i, vii). He suggests that plant systematists must, for the purpose of classification, consider the specific characters of plants to be constant (i.e unable to transmutate), but maintains that this is for practical and not theoretical reasons and that he is undecided on the question of species permanence: “There are other theories which claim more or less consideration from every unprejudiced naturalist; and there are such theoretical and practical difficulties (and perhaps impossibilities) in the way of our coming to any conclusion as to the limits of the species of many genera, as to give colour to the assumption that they have no permanently recognizable limits” (ix). This early hint at Darwin’s theory is then obscured by a lengthy exposition of arguments in favor of species permanence including the difficulty of producing varieties of plants under cultivation, retention of the same specific characters by widely dispersed plants, and the tendency for allied species to grow together without an apparent interchange of characters.
In an 1855 letter, Hooker wrote to Darwin of his changing views on species creation: “After all it is very easy to talk of the creation of a species in the Lyellian view of creation but the idea is no more tangible than that of the Trinity & to be really firmly & implicitly believed is…a believing in what the human mind cannot grasp. It is much easier to believe with you in transmutation, until you work back to the vital spark-a vis creatrix or whatever you may call it; which is a fact as inscrutable as a full blown species.” By 1859, Hooker’s journey to an evolutionary view of biodiversity was essentially complete, or, at the very least, finally made public. In his 1859 Introductory Essay to the Flora of Tasmania (also reprinted separately from the Botany of the Antarctic Voyage under the title On the Flora of Australia, Its Origins, Affinities, and Distribution; Being an Introductory Essay to the Flora of Tasmania), Hooker forthrightly acknowledges a change of viewpoint from that displayed in his 1853 Essay and openly champions the theory of natural selection put forward by Charles Darwin and Alfred Russell Wallace.
“In the present essay I shall advance the opposite hypothesis, that species are derivative and mutable; and this chiefly because, whatever opinions a naturalist may have adopted with regard to the origin and variation of species, every candid mind must admit that the facts and arguments upon which he has grounded his convictions require revision since the recent publications of the Linnaean Society of the ingenious and original reasoning and theories of Mr. Darwin and Mr. Wallace” (2).
Hooker divided the 1859 Introductory Essay into three sections entitled “On the General Phenomena of Variation in the Vegetable Kingdom,” “On the General Phenomena of Distribution in Area,” and “On the General Phenomena of the Distribution of Plants in Time.” In the first two sections he describes the evidence that he has observed as corresponding to Darwin’s “rationale,” including that there is more tendency to variation in plant species in nature than is usually accounted for; the ability of horticulturalists to turn cultivated plant species into new varieties; that plant species which do not survive in nature die because of their inability to compete with their “enemies;” and the general tendency of plants to radiate out from an area of common geographical origin. In the final section on the “Distribution of Plants in Time,” Hooker is more reticent, admitting that paleobotanical evidence “is not altogether favorable to the theory of progressive development, both because the earliest ascertained types are of such high and complex organization, and because there are no known plants which we can certainly assume to belong to a non-existing class or even family, nor that are ascertained to be intermediate in affinity between recent classes or families” (23).
Still, this does not prevent Hooker from leading up to his remarkable conclusion that “…if, as I have endeavored to show, all those attributes of organic life which are involved in the study of classification, representation, and distribution, and which are barren facts under the theory of special creations, may receive a rational explanation under another theory, it is to this latter that the naturalist should look for the means of penetrating the mystery which envelopes the history of species, holding himself ready to lay it down when it shall prove as useless for the further advance of science, as the long serviceable theory of special creations, founded on genetic resemblance, now appears to me to be” (26).
Darwin commented extensively on Hooker’s manuscript versions of the Introductory Essay to the Flora of Tasmania, writing to him with concerns about Hooker’s seeming to quote Origin which had not yet been published –“I am far more than satisfied at what you say of my work; yet it would be as well to avoid the appearance of your remarks being a criticism on my fuller work” – and complimented Hooker on his “grand” essay which would “convert botanists from the doctrine of immutable creations”. (To read in-depth correspondence between Hooker and Darwin during these crucial years, please visit the Darwin Correspondence Project and the Hooker Correspondence Project).
The American botanist Asa Gray, reprinted Hooker’s Introductory Essay in the American Journal of Science and Arts, writing in a footnote on the very first page:
“I asked and have received the distinguished author’s permission to reprint them…that we may have before us, at the earliest date, an essay which cannot fail to attract the immediate and profound attention of scientific men…To those who have intelligently observed the course of scientific investigation, and the tendency of speculation, it has for some time been manifest that a restatement of the Lamarkian hypothesis is at hand. We have this, in an improved and truly scientific form, in the theories which, recently propounded by Mr. Darwin, followed by Mr. Wallace, are here so ably and altogether independently maintained. When these views are fully laid before them, the naturalists of this country will be able to take part in the interesting discussion which they will not fail to call forth” (1).
As Asa Gray points out, in The Flora of Australia, Hooker’s conviction in the theory of natural selection is “altogether independently maintained”. Nor was Asa Gray the only botanist with whom Hooker corresponded about the theory of natural selection on the basis of his own botanical evidence. In an 1860 letter to the Irish botanist William Henry Harvey, Hooker advises him to “Remember that I was aware of Darwin’s views fourteen years before I adopted them, and I have done so soley and entirely from an independent study of the plants themselves” (Life and Letters, italics in original text). Harvey was reluctant to accept natural selection as cause of the establishment of particular plant varieties, but Hooker reminded him not to confuse natural selection with variation itself. Drawing on his own experience of the intellectual journey from species fixity to transmutation, Hooker writes, “I am extremely anxious that you should not commit yourself in your present state of very partial knowledge and strong feelings on a subject that requires years of thought and the calmest study, and above all a singleness of mind in seeking for truth at all hazards” (Life and Letters).
Although largely remembered as Darwin’s confidant and Director of the Royal Botanical Gardens at Kew during the peak of the British empire, Hooker played a critical role in the early history of evolutionary thought. He was central to the intellectual sparring and critique that helped Darwin advance his own case for transmutation. Perhaps equally important, Hooker was also in his own right one of the leading minds scrutinizing the evidence for and against an evolutionary explanation of life, and penning a critical piece of independent scholarship to bolster the case of descent with modification in 1859. [/expand]