November 24th, 2009 marked the 150th anniversary of the publication of Charles Darwin’s On the Origin of Species. The book, along with Marx’s The Communist Manifesto is the most important work of the 19th century. Like the other, Origin challenged both the scientific establishment and the social establishment, and as a result, generated a lot of controversy, which it continues to do so to this day.
Origin of Species must also be considered one of the most influential books of all time. I can’t think of any work that has so rapidly and in a such a way shifted the prevailing paradigm and changed humankind’s perception of the world and itself– so it’s no surprise that the book is said to have brought about a revolution in science, much like Copernicus’ On the Revolutions of the Celestial Spheres. Unlike Copernicus, however, Darwin himself foresaw this and wrote in the last pages of Origin:
When the views advanced by me in this volume, and by Mr. Wallace, or when analogous views on the origin of species are generally admitted, we can dimly forsee that there will be a considerable revolution in natural history. -Chapter XV, On the Origin of Species
In the words that follow, I explore the origins of Origin and pose that the revolution in fact started a year and some months earlier with the publication of the Linnean papers. I also examine the brilliant naturalist and elusive figure, “Mr. Wallace”, and his role in putting forward evolutionary theory.
The Linnean Papers
Darwin, Wallace & A Nascent Revolution
By Marzieh Ghiasi (Nov 2009)
n July 1st, 1858, in a special meeting of the Linnean Society, held in London, two brief papers describing natural selection as a mechanism of evolution were read. The Linnean papers, published later in August 20th as part of the society’s proceedings, were the start of a movement in science that became known as the Darwinian revolution. One essay was by Charles Darwin, an English naturalist whose name has become the cornerstone of evolutionary theory. The other essay was by Alfred Russel Wallace, an English naturalist whose name has become largely restricted to the annals of history. The traditional approach has been to set Darwin and Wallace as rivals in a fight for priority of publication, one which the majority of literature has argued Darwin won. The Linnean papers, however, can be examined as an outcome of a cooperative trajectory in which a common theory of evolution was developed by two vastly different individuals. This paper focuses on the association between Darwin and Wallace with respect to the Linnean papers, arguing that the interactions of the two naturalists offered them mutual benefits that would have been unlikely otherwise. As well, the interactions between the two men created a cohesion and unity critical in a field at its nascent stages.
Two Men Worlds Apart
Victorian Britain was highly class-conscious and its science was viewed as a domain of the upper class. Charles Darwin, born in 1809 into a prestigious and wealthy English family and educated in the University of Edinburgh and University of Cambridge, was an ideal representative of these values. Alfred Russel Wallace, conversely, was born in 1823 to a low income family and class relations played a tremendous role throughout his life. Although his father was a lawyer, he never practiced and the family had to learn to rely on self-sufficiency. Wallace never received formal schooling beyond the age of thirteen, when he was withdrawn and sent to an apprenticeship because his family no longer could pay for his education. By the time he was fourteen, he joined his brother as an apprentice land surveyor. However, Wallace was precocious and determined, and began to teach himself many subjects including taxonomy for which he had grown a great affinity. Unlike Darwin, who was well positioned for a life in pursuit of science, Wallace’s challenge was to break through rigid social barriers and prove himself as a scientist.
For both men, the connections they made with individuals proved to be invaluable throughout their lives. Charles Lyell and Joseph Dalton Hooker, both highly respected naturalists in their own right, were such scientific friends for Darwin. They played an important role in supporting him through his endeavors, specifically by encouraging him to publish his theories, as well providing a sounding board for his ideas and concerns. In 1843, unable to find work as a surveyor Wallace applied for teaching positions, and after many rejections acquired one in the city of Leicester. However, he still felt he was lacking in areas of study like Latin and Mathematics, and in order to compensate he spent much time in Leicester library. There he met Henry Walter Bates, who at nineteen had already published a paper as an entomologist. Like Wallace, Bates was also from a poor background, which along with their similar interests gave Wallace a life-long friend whose correspondence encouraged Wallace to further pursue his studies in natural sciences.
Principles: Theoretical Foundations
The concept of transformation of species did not originate in the 19th century, but had a long history in western thought. Anaximander (611-543 BCE), an Ionian philosopher had posited that animals and humans were not present in the early stages of the universe, but developed progressively. Empedocles (490–430 BCE), a Greek philosopher had hypothesized that animals that were unfit to live have had must have died out after creations. Lucretius (99-55 B.C.E.), a roman poet and philosopher wrote De Rerum Natura (“On the Nature of Things”) which described a process of selection and elimination which ensured the extinction of once-living creatures and survival of agile, strong, and “useful” creatures. These hypotheses, however, largely drew on mythology and did not have any empirical basis.
The late 18th century brought on a fresh wave in evolutionary theory. One of the prominent figures in this movement was Erasmus Darwin, Charles Darwin’s grandfather. Darwin as a youth was very much inspired by Erasmus Darwin who in his book Zoonomia outlined transmutation and anticipated Lamarckism. This early-set view may explain Darwin’s later beliefs in some Lamarckian principles including soft inheritance, that hereditary material is susceptible to environmental principles, which Wallace categorically rejected. As the ideas of Darwin and Wallace matured, three works had similar influences on both of them, namely Malthus’ Principle of Population, Lyell’s Principles of Geology, and Vestiges of the Natural History of Creation by Robert Chambers.
Thomas Malthus’ An Essay on the Principles of Population was first published in 1798. There has been some debate as to whether Malthus should be considered a contributor or an instigator of evolutionary theory. Wallace thought of him as an instigator, and when speaking about his relationship with Darwin in 1908 at the Linnean Society, focused on the fact that they had had both read Malthus’ book which he said it “led us immediately to the simple but universal law of the Survival of the Fittest.” Although Wallace had read the essay ten years prior to the publication of the Linnean papers, he greatly admired it and it came back to him when he was writing the draft of his paper. Darwin first read Malthus in 1838, two years after he returned from his voyage on the Beagle and having just started a note book on the transmutation of species. There is no doubt that the book had a strong influence on him, as he describes natural selection in the Origin of Species as the “doctrine of Malthus applied with manifold force to the whole animal and vegetable kingdoms.”
Charles Lyell developed and popularized the concept of uniformitarianism, the principle which suggests that universal laws that apply in present time existed in the past as well. Specifically applied to geology, he viewed the earth, rather than being shaped by catastrophes, as being shaped by accumulating changes over long spans of time. Darwin and Wallace were both greatly influenced by the principles set out by Lyell. Darwin had formed a good friendship with Lyell and took the first volume of Principles of Geology, which was published in 1830, and subsequent volumes on his first Beagle Voyage. Wallace also greatly admired Lyell and carried his Principles of Geology along with him on his expeditions. He found the observations by Lyell to be particularly useful as he conducted biogeographical surveys. Wallace’s Annals paper published in 1855 was heavily influenced by Lyell’s principles.
In 1844, while Darwin was expanding his preliminary sketches of evolutionary theory and young Wallace was working as a tutor in Leicester, the Vestiges of the Natural History of Creation was published. The author, Robert Chambers, published anonymously because he feared that his work would be received as blasphemous. The book was a hypothetical dissertation which described a scala natura, a “chain of being” connecting different animals, and described a process of transmutation by which species had developed. The work was decried by many individuals as one that “undermined the whole moral and social fabric.” The book was also criticized for being unphilosophical by prominent scientific figures of the time like Thomas Henry Huxley, who would become a strong advocate of Darwinism. In a letter to Huxley, Darwin mildly criticized the book, holding however that his own ideas on species were “almost as unorthodox… as the ‘Vestiges’…though… not quite so unphilosophical.” Wallace read the work in 1845 and found the ideas compelling, raising more than ever his interest in the origin of species.
Expeditions: Empirical Foundation
It is often noted that Darwin and Wallace both undertook journeys which had tremendous influences on them. However, despite similarities in the theoretical foundations of the Linnean papers, Darwin and Wallace arrived at the theory of natural selection differently empirically. First, Wallace formulated his theories largely based on field observations. Darwin on the other hand conducted experiments and collected data on artificial breeding, thus basing his theories largely on experimental observations. Second, Darwin and Wallace differed on how they arrived at a mechanism for evolution. Darwin had developed the concept of natural selection in his early notes, which he later connected to divergence. Wallace, however, developed a principle of divergence, published in his 1855 paper, and then arrived at the theory of natural selection. Finally Wallace’s main breakthroughs were the result of moments of inspiration, while Darwin’s breakthrough came after painstaking analysis for many years.
Wallace was in many ways a natural explorer who spent the majority of his time prior to the publication of the Linnean papers traveling first to the Amazon, then to East Asia where he formulated his theory. In 1848, the twenty-five year old Wallace headed to the Amazon with close friend Bates. But while Bates was focused on collecting insects, Wallace had a broader collection that came from his interest in addressing the speciation puzzle. Separating from Bates in order to expand his collection, Wallace went on a four year expedition up Rio Negro. He also traveled in “one of the great heroic feats of natural history exploration” to Columbia and charted regions that had never been seen by Europeans. Wallace returned to London in October of 1852, having lost his entire collection and the majority of his notebooks to a ship fire. Nonetheless, Wallace was a prolific writer and published a book on his travels in the Amazon, which Darwin later on criticized for lacking facts. Only eighteen months after returning from South America Wallace headed to the Malay Archipelago. He arrived in Singapore and headed to Sarawak state of the Malay Borneo, where he had been invited by Sir James Brooke, the English Rajah of the state.
Here Wallace he developed his “Sarawak Law” paper entitled On the Law which has Regulated the Introduction of New Species, published in Annals and Magazine of Natural History in September of 1855. The paper examined geographical divisions of animals throughout lands and formulated the setting of evolution, the where and when, but lacked an adequate mechanism to describe how these changes had occurred. The paper was supported by Wallace’s charts and meticulous observational recordings; the formulation was by all accounts innovative and laid the groundwork for evolutionary theory. It was described later by Huxley as a “powerful essay” which brought Wallace to “the center of the Victorian evolutionary Maelstrom.” However, at the time of its publication there was not much reaction to the paper, which surprised Wallace. Despite the subdued reaction, both Darwin and Lyell had actually read Wallace’s essay. Although Darwin himself held that his views had not been influenced by Wallace, the formulation of the divergence principle, which Darwin himself had not quite worked out, may have at the very least helped Darwin synthesize his ideas.
Despite the similarities in interests Darwin and Wallace were not actually acquaintances until near the publication of the Linnean papers in 1858. This can be largely attributed to the fact that Wallace was away from Britain. They did accidentally encounter one another in late 1853 in the British Museum where Wallace had been studying zoological collections in preparation for his Malay expedition. In this encounter, as recollected by Wallace, “nothing of importance” was discussed. Wallace, himself young and relatively unknown, was well aware of the reputation of Darwin in the scientific circles of London. He had enjoyed Darwin’s book The Voyage of the Beagle (1839) as a youth and was eager to correspond with Darwin. In 1955, while Wallace was in the Malay Archipelago, Darwin contacted him in order to obtain some domesticated specimens from the region. Wallace was more than enthusiastic to support Darwin, supplying more species than he asked for.
In May of 1857, Darwin corresponded with Wallace regarding Wallace’s 1855 publication in the Annals stating positively that “we have thought much alike and to a certain extent have come to similar conclusions… I agree to the truth of almost every word of your paper…” However later in the letter he mentioned his own book which he anticipated would be published in two years’ time. Some authors have viewed this as move to intimidate Wallace or to establish priority. While this may have been the case, as Darwin’s close friends urged him to establish priority, other correspondences between the two reveals an amicable and supportive relationship. Wallace sent a letter to Darwin inquiring about the progress on his book, as well, expressing his own discouragement at having received so little reaction for his own article in the Annals. Darwin wrote to him in December of 1857 with words of enouragement “you must not suppose that your paper has been attended to: two very good men, Sir C. Leyell, and Mr E. Blyth of Calcutta, specially called my attention to it.” Theses exchanges must have encouraged and stimulated Wallace tremendously as he wrote his synthesized paper only a few months later, in February of 1857.
Synthesis of a Theory
Having encountered upon Wallace’s article in the Annals and Magazine of Natural History in May of 1856, Lyell found similar ideas presented in the article which he had over time discussed with Darwin. Sensing that Wallace was heading in the same direction, Lyell urged Darwin to publish, writing to him “I wish you would publish some small fragment of your data pigeons if you please & so out with the theory & let it take date- & be cited- & understood.” Darwin however responded to Lyell by stating that he did not have all the facts he needed to publish his theory and was not willing to publish for the sake of priority. Nonetheless, he admitted that he would be “vexed if any one were to publish my doctrines before me”. It appears that that while Lyell considered Wallace a threat at that time and pushed Darwin to establish priority, Darwin himself did not and remained reluctant to publish.
One reason Darwin was hesitant to publish his theories may have been the fear of the effect it would have on his family and his reputation. Those involved in developing evolutionary theory were quite aware of the threat that evolutionary theory represented to the religious establishment. Although with the popularization of Lamarckism the notion of transmutation of species had gained popularity, the Victorian society nonetheless remained hostile to evolutionary theory as they associated it with the age of enlightenment, which the English blamed for the French revolution. The strongly negative reactions to Vestiges of the Natural History of Creation in 1844 highlighted the challenge that evolution presented to the orthodoxy, and the fear that the rejection of natural theology for natural philosophy would lead to collapse of morality and by extension the state. Indeed, soon after he published On the Origin of Species, in1859, Darwin received a letter from Huxley affirming his support for Darwinian evolutionary theory “As for your doctrines I am prepared to go to the stake if requisite…” While the term stake is used facetiously given the practices of the time, Huxley anticipated severe criticism from the religious establishment stating “I trust you will not allow yourself to be in any way disgusted or annoyed by the considerable abuse and misrepresentation which unless I greatly mistake is in store for you.”
Meanwhile, Wallace, had in the beginning of 1858 moved to Ternate, an island off the east-coast of Indonesia. In this rainy place, he was restricted to home much of the time and stricken with bouts of malaria. It was at that time that he wrote what would become his part of the Linnean papers. Wallace later recounted in his autobiography how in the February of 1858, while ailing with malaria, he began to write on the survival of the fittest by natural selection: “During one of these fits, while again considering the problem of the origin of species, something led me to think of Malthus’ ‘Essay on Population’ (which I had read about ten years before)… in the two hours of my fit I had thought out the main points of the theory.” Wallace did not mention Malthus directly in his paper. However, recounting his writing process he mentioned that Malthusian ideas had helped him explain the struggle between varieties. “From the effects of disease the most healthy escaped, from enemies, the strongest, the swiftestst, or the most cunning… Then it suddenly flashed upon me… in every generation the inferior would be inevitably killed off and the superior would remain—that is, the fittest would survive.” The paper was entitled On the Tendency of Varieties to Depart Indefinitely from the Original Type and was completed in the span of several days, and forwarded to Charles Darwin.
The Linnean Arrangement
Established on the basis of a large collection belonging to the father of taxonomy, Carl von Linnaeus, the Linnean Society of London was one of the most powerful and respected scientific societies in Britain in 1885. There has been much speculation surrounding the circumstances around which the Linnean papers were presented. By a strange twist of fate, the Linnean society meeting of that year had been moved forward due to the death of its president from June 17th of 1858 to July 1st. Wallace’s letter, including the manuscript of his theory, arrived at Darwin’s residence on June 18th of the same year and it took 12 days for an arrangement to be made to present joint papers by Wallace and Darwin.
The arrival of Wallace’s packet greatly distressed Darwin, who now feared having been forestalled from publishing the theory of natural selection which he had been working on for 20 years. He wrote to Lyell and Hooker that he was not only distressed by the prospect of having been forestalled, but also by a dilemma he faced. Specifically, Wallace had not stated anything regarding publication. However, Darwin felt that having been in possession of Wallace’s document, publishing his own paper would be dishonorable as he perceived Wallace’s to be “a succinct but perfect statement of [his] own theory of evolution by natural selection.” A reading of the Linnean papers shows that while only Darwin used the term “natural selection”, the two papers indeed share many commonalities. It has recently been suggested, though, that theory as presented in Wallace’s manuscript was in fact not identical to that of Darwin. But, a distressed Darwin misinterpreted it to be so, and he in turn “biased Hooker and Lyell”. To Darwin’s relief though, Lyell and Hooker were able to come up with an alternative arrangement in which the papers by both Darwin and Wallace would be presented to the society.
At the meeting held on July 1st, 1885, there were many papers to be presented, notably one on the fixity of species by George Bentham. Notwithstanding, Lyell and Hooker persuaded the secretary to include the two papers in the programme. Darwin’s paper was a five-page summary extracted from his 1844 sketch, in addition to a letter which Darwin had sent to American botanist Asa Gray the year prior. Noting that Wallace’s paper was read after that of Darwin, Arnold Brackman has argued in A Delicate Arrangement that in this bargain, Wallace was not given the credit due as the first individual to publicly articulate the theory of natural selection. While Wallace’s paper was groundbreaking, he was a relatively obscure naturalist and the fact that his paper was supported by Lyle, Hooker, not to mention a naturalist of high standing like Darwin tremendously helped it. This was something that Wallace recognized as following the publication of his paper he wrote home that Darwin had shown his essay to “Dr Hooker and Sit C. Lyell, who thought so highly of it that they immediately read it before the Linnean Society,” ensuring Wallace “the acquaintance and assistance of these eminent men on [his] return home.”
The meeting proceeded with five more papers, although following the reading of Darwin and Wallace’ papers George Bentham withdrew his fixity of species paper, neither Darwin or Wallace were present at the meeting, and the papers were not openly discussed. Nor was significance of the Linnean papers immediately grasped by all, as the meeting was described as uneventful by Thomas Bell, the president, who in his annual report said “The year which has passed… has not been unproductive in contributions of interest and value…it has not indeed been marked by any of those striking discoveries which at once revolutionize…”
A Nascent Revolution
I. Bernard Cohen has argued that the Linnean papers did not produce the Darwinian revolution; rather it was Darwin’s On the Origin of Species that was responsible. The Linnean papers, published a year before Origin, indeed did not create a very public outpouring of interest. However, they stirred the scientific community and brought into forefront the summary of a theory supported not by one individual, but by some of the most prominent scientific figures of the time. The publication of the Linnean papers urged Darwin to publish his work, and continue to expand on it while he was alive. As pointed out by Huxley in a letter in 1858 to Hooker “Wallace’s impetus seems to have set Darwin going in earnest.” More importantly, however, the Linnean papers created a receptive environment for Darwin to publish his book. In that way the Linnean papers were the birth of a revolution that was reinforced by Darwin’s magnum opus.
The relationship of Darwin and Wallace following the publication of the Linnean papers was marked with complexities. However, in the time immediately following, they enjoyed a close friendship and tremendous mutual respect. Darwin specially admired Wallace’s writing, and in fact he wrote to Bates, whom he had become acquainted with, “Some are born with a power of good writing, like Wallace. Others like myself & Lyell have to labour very hard & long at every sentence.” As well, Darwin recognized the value of Wallace’s support in popularization of evolutionary ideas as he wrote to Wallace in 1866 “thank you for your paper on pigeons, which interested me, as everything that you write does… I finished yesterday your paper in the Linnean Transactions. It is admirably done. I cannot conceive that the most firm believer in Species could read it without being staggered. Such papers will make many more converts among naturalists than long-winded books such as I shall write if I have the strength.”
Although Wallace had technically been the first to put his thesis on natural selection in a publishable form, he continued to give credit to Darwin for its discovery and never claimed priority. This has been viewed, in combination with other factors, to have played an important role in his almost “forgotten status” in the history of science. However, for Wallace it appears that beyond being satisfied with being associated with the “scientific elite” of Britain and grateful for the friendship and support of Darwin Wallace may have sensed the importance of maintaining a harmonious front at the nascent stages of this particular revolution, by completely and fully devoting himself to Darwinism, instead of pitting himself against Darwin. This perhaps explains why even as Wallace and Darwin’s theoretical perspectives began to diverge in later years, Wallace continued to consider himself to be a Darwinist despite disagreeing with Darwin.
The Darwinian revolution has been compared to the much earlier Copernican revolution both in its impact in invigorating a new era in western science, and its transformation of societal consciousness on human origins and place in the universe. It is perhaps paradoxical that “Darwin’s Century” should be the Victorian area with its rigid social hierarchies, and general disdain for disestablishment and those who sought to divorce science from theology. It is also interesting that one of the greatest scientific minds of this era, Alfred Russel Wallace, was an autodidact from the lower strata of the society. But perhaps it is very appropriate that a movement challenged man’s place in the universe, and descended him to the same plane as fish and apes came at the closing of the enlightenment; and one of its instigators was part of the rising working class.
The collaboration between Darwin and Wallace was one of mutual respect and offered benefits that would have been unlikely otherwise. A humble Darwin, despite his background and education, viewed Wallace, who never had a formal education beyond the age of thirteen as his equal and even greater in some respects. Furthermore, Darwin encouraged Wallace and saw within him tremendous potential. As well, despite every motivation to do otherwise, he acted honorably upon receiving Wallace’s unexpected paper and reluctantly presented his own alongside it; which had he been a different individual, might have turned out differently. Wallace admired Darwin and through his correspondence came to trust him, which is why he sent his contribution to the Linnean papers to him in 1858. Following the publication of the paper, Wallace expressed gratitude to Darwin for his support. Instead of focusing on receiving greater credit and recognition for his contribution to evolutionary theory, a self-effacing Wallace recognized that nurturing the nascent Darwinian revolution, the new paradigm in science, was preferable to dividing it. This is best illustrated by Wallace’s strong recommendation to a friend about Darwin’s On the Origin of Species on the eve of its publication, on November 24th 1859, precisely 150 years ago: “Mr. Darwin has given the world a new science, and his name should, in my opinion, stand above that of every philosopher of ancient or modern times.”
 ibid, p. 20.
 ibid, p. 23.
 ibid, p. 92.
 Bowler, P. J. (2003). Evolution : the history of an idea. Berkeley: University of California Press.
 Hodge, M. J. S., & Radick, G. (2003). The Cambridge companion to Darwin. pp. 49-50.
 Wilson, J. G. (2000). The forgotten naturalist : in search of Alfred Russel Wallace. Melbourne: Australian Scholarly Publishing, p. 288.
 Cohen, I. B. (1985). Revolutions in science. Cambridge, Mass.: Harvard Univ. Press. p. 293.
 Wilson, 2000, p. 186.
 Wallace, A. R. (1905). My life : a record of events and opinions. London: Chapman & Hall, Ld. p. 232.
 Darwin, C., & Barlow, N. D. (1958). The autobiography of Charles Darwin, 1809-1882. With original omissions restored. New York: Harcourt, Brace. p. 87.
 Darwin, C. (1882). The origin of species by means of natural selection, or, The preservation of favoured races in the struggle for life. London: John Murray p. 99.
 Lyell, C. (1873). Principles of geology; or, The modern changes of the earth and its inhabitants considered as illustrative of geology. New York: D. Appleton. pp. 1-5.
 Darwin & Barlow, 1958, p. 49.
 Wilson, 2000, p. 85.
 Slotten, 2004, p. 28.
 Desmond, A. (1989). The politics of evolution : morphology, medicine, and reform in radical London. Chicago: Univ. of Chicago Press. pp. 178.
 Slotten, 2004, p. 30.
 ibid, p. 153.
 Wilson, 2000, p. 41.
 ibid, p. 33.
 ibid, p. 45.
 ibid, p. 50.
 ibid, p. 87.
 Brackman, A. C. (1980). A delicate arrangement : the strange case of Charles Darwin and Alfred Russel Wallace. New York: Times Books. pp. 38.
 Fichman, M. (2004). An elusive Victorian : the evolution of Alfred Russel Wallace. Chicago: University of Chicago Press. p. 87.
 Slotten, 2004, p. 91.
 ibid, p. 121.
 Burkhardt, F. H. (1990). The correspondence of Charles Darwin: 1856 – 1857. Cambridge [u.a.]: Cambridge Univ. Press. p. 387.
 Slotten, 2004, p. 135.
 ibid, p. 88.
 Burkhardt, 1990, p. 514.
 Burkhardt, 1990, p. 89.
 Slotten, 2004, p. 122.
 Wilson, 2000, p. 88.
 Fichman, 2004, p. 75.
 Desmond, 1989, p. 178.
 Huxley, L. (2007). Life and Letters of Thomas Henry Huxley — Volume 1. Teddington: Echo Library. p. 153.
 ibid, p. 153.
 Wilson, 2000, p. 174.
 Brackman, 1980, p. 199.
 Wallace, A. R. (1905). My life : a record of events and opinions. London: Chapman & Hall, Ld. pp. 361-362.
 Linnean Society of, L. (1859). Zoological journal of the Linnean Society. Zoological journal of the Linnean Society., 3-4. p. Liii.
 Slotten, 2004, p. 154.
 De Beer, G. (1965). Charles Darwin: a scientific biography. Garden City, N.Y.: Doubleday, Published in co-operation with the American Museum of Natural History. p. 148.
 Bock, W. J. (2009). The Darwin -Wallace myth of 1858. Proceedings of the Zoological Society, 62(1), 1-12.
 Wilson, 2000, p. 180
 Brackman, 1980, p. 84
 Fichman, 2004, p. 100.
 Bowlby, J. (1992). Charles Darwin : a new life. New York: W.W. Norton. p. 345.
 Wilson, 2000, p. 182.
 Cohen, 1985, p. 288.
 Huxley, 2007, p. 187.
 Clodd, E. (1926). Memories. London: Watts. pp. 64-65.
 Marchant, J. (1916). Alfred Russel: Letters and Reminiscences. London: Cassel and Company. p. 166.
 Wilson, 2000, p. 183.
 Fichman, 2004, p. 101.
 Wilson, 2000, p. 186.
 Wallace, 1905, p. 374.