The best-known controversies over Darwinian theory took place in public or in printed reviews. Many of these were highly polemical, presenting an over-simplified picture of the disputes. Letters, however, show that the responses to Darwin were extremely variable. Many of his strongest public supporters, such as Thomas Henry Huxley, Joseph Dalton Hooker, and Asa Gray, continued to have sharp theoretical differences with him; on the other hand, a number of his public critics assisted his research privately. Correspondence was itself an important arena of debate, one that Darwin greatly preferred to the public sphere. Often sharp disagreements could be resolved or overcome, and friendship and support sustained in spite of enduring differences. Darwin's correspondence can thus help broaden our understanding of the role of scientific controversy and the ways in which it was conducted in the nineteenth century.
Disagreement and Respect
Darwin rarely engaged with critics publically. Letters exchanged with Adam Sedgwick, professor of geology at Cambridge, and Richard Owen, the eminent comparative anatomist, show how Darwin tried to manage strong disagreement in the more private realm of correspondence. In the case of Sedgwick, Darwin was able to remain on friendly and respectful terms with his former professor. In the case of Owen, however, though their theoretical differences were less severe, the relationship quickly deteriorated and Darwin came to regard him as a bitter enemy.
Darwin and Sedgwick
Letter 2525 — Darwin, C. R. to Sedgwick, Adam, 11 Nov 1859
Darwin writes to Sedgwick to tell him that he has contacted his publisher John Murray to send him a copy of Origin. Darwin’s conclusion is diametrically opposed to that which Sedgwick has often advocated, but he assures Sedgwick he does not send his book out of a spirit of bravado, but a want of respect.
Letter 2548 — Sedgwick, Adam to Darwin, C. R., 24 Nov 1859
Adam Sedgwick thanks Darwin for the Origin. Sedgwick has read the book “with more pain than pleasure”. He says Darwin has deserted “the true method of induction” and many of his wide conclusions are “based upon assumptions which can neither be proved nor disproved”. He says that Darwin’s “grand principle natural selection” is “but a secondary consequence of supposed, or known, primary facts” He ends by saying he writes in the spirit of brotherly love and as his true-hearted friend.
Letter 2555 — Darwin, C. R. to Sedgwick, Adam, 26 Nov 
Darwin says Sedgwick could not have paid him a more honourable compliment than expressing freely his “strong disapprobation” of his book. He is grieved “to have shocked a man whom I sincerely honour”. He mentions that he has worked “like a slave” on the subject for over 20 years and is not conscious that bad motives have influenced the conclusions at which he has arrived. Darwin does not think the book will be mischievous and states: “if I be wrong I shall soon be annihilated”. Darwin may have written too confidently from feeling confident that no “false theory would explain so many classes of facts”.
Darwin and Owen
Letter 2526 — Owen, Richard to Darwin, C. R., 12 Nov 1859
Owen says to Darwin he will welcome his work [Origin] with a “close & continuous perusal”. He believes in the “operation of existing influences or causes in the ordained becoming and incoming of living species” and so could not regard Darwin’s attempt to demonstrate the nature of such influences as “heterodox”.
Letter 2575 — Darwin, C. R. to Lyell, Charles, [10 Dec 1859]
Darwin discusses with King's College, London Professor of geology, Charles Lyell at length a conversation with Owen concerning Origin. Darwin notes “that at bottom he goes immense way with us”, but emphasises Owen’s unfriendly manner. Darwin remarks that Owen accepted a relationship between bears and whales: “By Jove I believe he thinks a sort of Bear was the grandpapa of Whales!” Darwin has heard Herschel considered his book “the law of higgledy-piggledy”.
Letter 2580 — Darwin, C. R. to Owen, Richard, 13 Dec 
Darwin responds to Owen’s remarks that his book [Origin] is not likely to be true because it attempts to explain so much. Darwin describes how, for fear this might be so, he resolved to give up the work if he could not convince two or three competent judges. He is sensitive because of “unjust things” said by a “very distinguished friend” [A. Sedgwick]. Value of his views now depends on men eminent in science.
Letter 2767 — Darwin, C. R. to Gray, Asa, 25 Apr 
Darwin discusses Origin reviews with Harvard botanist Asa Gray. Darwin is annoyed at Owen’s malignity [Edinburgh Rev.111 (1860): 487–532].
Conduct of Debate
Darwin usually avoided public controversy, and he is sometimes thought to have withheld his views on religion or human nature because he feared adverse public reaction. This exchange of letters with the zoologist Ernst Haeckel, an ardent proponent of Darwinism and a stern critic of religious authority in Germany, shows that Darwin had strong reservations about the value of polemical debate in science, and a deep optimism that the truth would eventually prevail without such aggressive tactics.
Letter 5500 — Darwin, C. R. to Haeckel, E. P. A., 12 Apr 
Darwin is sympathetic to Haeckel’s position, and is struck by singular clarity of his Generelle Morphologie. However, he is concerned that the remarks on various authors seem too severe. He believes that severity leads the reader to take the side of the attacked person.
Letter 5533 — Haeckel, E. P. A. to Darwin, C. R., 12 May 1867
Haeckel thanks Darwin for the new edition of Origin [4th ed. (1866)]. He comments on Darwin’s criticism of the harsh tone of Generelle Morphologie. He may have harmed himself, but does not believe he has harmed his cause. He believes a radical reform of the science necessary. Since most scientists take a prejudiced view of the matter, a vigorous attack is essential.
Letter 5544 — Darwin, C. R. to Haeckel, E. P. A., 21 May 
Darwin discusses his previous criticisms of Haeckel’s Generelle Morphologie. He fears Haeckel will make enemies. He discusses reception of descent theory in England.
Darwin and Wallace
Much has been written about the 'co-discovery' of natural selection by Darwin and Alfred Russel Wallace, and some have argued that Wallace received insufficient credit. Letters exchanged between Darwin and his close friends, Joseph Dalton Hooker and Charles Lyell, show that Darwin, who had worked on the theory for twenty years, was very upset at the prospect of losing priority to Wallace, while at the same time wanting to acknowledge Wallace's contribution fully. The initial presentation of the theory through joint papers at the Linnean Society of London, and presided over by Lyell and Hooker, reveals much about the social structure of Victorian science. Wallace would become one of Darwin's most valued correspondents and their relationship was one of strong mutual respect and support despite important theoretical, political, and religious differences.
Letter 2285 — Darwin, C. R. to Lyell, Charles, 18 [June 1858]
Darwin writes to Lyell and encloses a manuscript by naturalist A. R. Wallace. Darwin has been forestalled. “ . . . if Wallace had my MS sketch written out in 1842 he could not have made a better short abstract!” Wallace does not say if he wishes Darwin to publish the MS, but Darwin will offer to send it to journal.
Letter 2294 — Darwin, C. R. to Lyell, Charles, [25 June 1858]
Darwin writes to Lyell saying that everything in Wallace’s sketch also appears in his sketch of 1844. A year ago Darwin sent a short sketch of his views to Asa Gray. Can Darwin honourably publish his sketch now that Wallace has sent an outline of his views? He concludes: “I would far rather burn my whole book than that he or any man shd. think that I had behaved in a paltry spirit.” He does not believe Wallace originated his views from anything Darwin wrote to him.
Letter 2295 — Darwin, C. R. to Lyell, Charles, 26 [June 1858]
Darwin writes to Lyell and wonders: is it fair to take advantage of knowing that Wallace is in the field? It seems hard on Darwin to lose priority after so many years, but he does not feel this alters the justice of case.
Letter 2306 — Darwin, C. R. to Hooker, J. D., 13 [July 1858]
Darwin writes to Hooker, saying his letter to Wallace is perfect. Darwin explains his http://essaychecker.net feelings about priority. He says without Lyell’s and Hooker’s intervention, he would have given up all claims to Wallace. He is now planning a 30-page abstract for a journal.
Letter 2337 — Wallace, A. R. to Hooker, J. D., 6 Oct 1858
Darwin thanks Hooker and Lyell for the actions they have taken with respect to Wallace’s and his papers. He considers himself fortunate to have been given any merit for his work. Darwin is pleased that his correspondence has led to the earlier publication of his work. It would have caused him “much pain & regret” if his work had made Wallace’s paper public unaccompanied by his own views.
Letter 6024 — Wallace, A. R. to Darwin, C. R., 19 Mar 1868
Wallace writes to Darwin with a number of requests: for a photograph, a carte, for Darwin’s son to answer a query, and an invitation to discuss sterility of natural species and natural selection. He claims that closely allied forms from adjacent islands offer best chance of finding good species fertile inter se. He also discusses the problem of minute variations and sexual selection.
Letter 6033 — Darwin, C. R. to Wallace, A. R., [21 Mar 1868]
Darwin lets Wallace know he has sent the query to his son, will send a photo, and a carte. On problem of sterility, Darwin cannot persuade himself that it has been gained by natural selection. On sexual selection and minute variations, he tends to agree with Wallace. He sends George Darwin’s notes on Wallace’s argument.
Letter 6045 — Wallace, A. R. to Darwin, C. R., 24 Mar 
Wallace returns George Darwin’s criticisms of his notes on sterility and sends further notes in reply. He writes that since there are degrees of sterility between varieties, “is it not probable that natural selection can accumulate these variations?” He believes that varieties that are adapted to new conditions could then survive and form new species without being isolated.
Letter 6058 — Darwin, C. R. to Wallace, A. R., 27 Mar 
Darwin writes to Wallace saying his son “has failed in your problem & says that it is ‘excessively difficult’.” He claims that there are so many doubtful points on the problems relating to sterility that they will never agree.
Letter 6095 — Darwin, C. R. to Wallace, A. R., 6 Apr 
Darwin writes to Wallace on the “terrible problem” of natural selection and sterility. Darwin analyses and answers Wallace in detail in defence of his conclusion that sterility cannot be increased through natural selection.
Letter 6104 — Wallace, A. R. to Darwin, C. R., 8 [Apr] 1868
Wallace says if Darwin is not convinced by his notes on sterility, Wallace has little doubt that he is wrong. In fact, he was only half-convinced by his own arguments. Wallace modifies his first proposition [a species varies occasionally in two directions, but owing to free inter-crossing the variations never increase] and further discusses the subject. Wallace encloses Berthold Seemann’s notes on flora of the Hawaiian Islands. He says the presence of European alpine species in Hawaiian volcanoes is a “hard nut” for geographical distribution [but see Wallace’s Island life (1880), p. 323].