Great Hippocampus Question
The Great Hippocampus Question was a 19th-century scientific controversy about the anatomy of ape and human uniqueness. The dispute between Thomas Henry Huxley and Richard Owen became central to the scientific debate on human evolution that followed Charles Darwin's publication of On the Origin of Species. The name comes from the title of a satire the Reverend Charles Kingsley wrote about the arguments, which in modified form appeared as "the great hippopotamus test" in Kingsley's 1863 book for children, The Water-Babies, A Fairy Tale for a Land Baby. Together with other humorous skits on the topic, this helped to spread and popularise Darwin's ideas on evolution.
The key point that Owen asserted was that only humans had part of the brain then known as the hippocampus minor, and that this gave us our unique abilities. Careful dissection eventually showed that apes and monkeys also have a hippocampus minor.
Background
In October 1836 Charles Darwin returned from the Beagle voyage with fossil collections which the anatomist Richard Owen described, contributing to the inception of Darwin's theory of natural selection. Darwin outlined his theory in an Essay of 1844, and discussed transmutation with his friend Joseph Dalton Hooker. He did not tell Owen, who as the up-and-coming "English Cuvier" held the conventional belief that every species was uniquely created and perfectly adapted. Owen's brilliance and political skills made him a leading figure in the scientific establishment, developing ideas of divine archetypes produced by vague secondary laws similar to a form of theistic evolution, while emphasising the differences separating man from ape. At the end of 1844 the anonymous book Vestiges of the Natural History of Creation brought wide public interest in transmutation of species and the idea that humans were descended from apes, and after a slow initial response, strong condemnation from the scientific establishment.Darwin discussed his interest in transmutation with friends including Charles Lyell, and Hooker eventually read Darwin's Essay in 1847. When Thomas Henry Huxley savagely reviewed the latest edition of Vestiges in 1854, Darwin wrote to him, making friends while cautiously admitting to being "almost as unorthodox about species". Huxley had become increasingly irritated by Owen's condescension and manipulation, and having gained a teaching position at the school of mining, began openly attacking Owen's work.
Hippocampus minor
In 1564 a prominent feature on the floor of the lateral ventricles of the brain was named the hippocampus by Aranzi as its curved shape on each side supposedly reminded him of a seahorse, the Hippocampus. At that same time a ridge on the occipital horn was named the calcar avis, but in 1786 this was renamed the hippocampus minor, with the hippocampus being called the hippocampus major.File:Gray739-emphasizing-hippocampus-minor.png|thumb|left|alt=brain, cut away and labelled to show its internal parts|The hippocampus minor is a small fold on the occipital horn towards the back of the brain to the rear of the hippocampus major which forms a curved ridge on each side of the lower central area.
Richard Owen presented several papers on the anatomical differences between apes and humans, arguing that they had been created separately and stressing the impossibility of apes being transmuted into men. In 1857 he went even further, presenting an authoritative paper to the Linnean Society of London on his anatomical studies of primate brains and asserting that humans were not merely a distinct biological order of primates, as had been accepted by great anatomists such as Carl Linnaeus and Georges Cuvier, but a separate sub-class of mammalia, distinct from all the other primates and mammals generally. Owen supported his argument with a figure by himself of a South American monkey, a figure of a Khoekhoe woman's brain by Friedrich Tiedemann, and of a chimpanzee's brain by Jacobus Schroeder van der Kolk and Willem Vrolik.
While Owen conceded the "all-pervading similitude of structure—every tooth, every bone, strictly homologous" which made it difficult for anatomists to determine the difference between man and ape, he based his new classification on three characteristics which to him distinguished mankind's "highest form of brain", the most important being his claim that only the human brain has a hippocampus minor. To Owen in 1857, this feature together with the extent to which the "posterior lobe" projected beyond the cerebellum and the presence of the posterior horn were how man "fulfills his destiny as the supreme master of this earth and of the lower creation." Charles Darwin commented, "Owen's is a grand Paper; but I cannot swallow Man making a division as distinct from a Chimpanzee, as an ornithorhynchus from a Horse: I wonder what a Chimpanzee wd. say to this?". Owen repeated the paper as the Rede Lecture at the University of Cambridge on 10 May 1859 when he was the first to be given an honorary degree by the university.
To Thomas Henry Huxley the claim about the hippocampus minor appeared to be a significant blunder by Owen, and Huxley began systematically dissecting the brains of monkeys, determined that "before I have done with that mendacious humbug I will nail him out, like a kite to a barn door, an example to all evil doers." He did not discuss this in public at this stage, but continued to attack Owen's other ideas, aiming to undermine Owen's status. At his 17 June 1858 Royal Institution Croonian Lecture "On the Theory of the Vertebrate Skull", Huxley directly challenged Owen's central idea of archetypes shown by homology, with Owen in the audience. Huxley's aim was to overcome the domination of science by wealthy clergymen led by Owen, in order to create a professional salaried scientific civil service and make science secular. Under Darwin's influence he took up transmutation as a way of dividing science from theology, and in January 1859 argued that "it is as respectable to be modified monkey as modified dirt".
Owen and Huxley debate human and ape brain structure
Huxley was among the friends rallying round the publication of Darwin's On the Origin of Species, and was sharpening his "beak and claws" to disembowel "the curs who will bark and yelp". Charles Kingsley was sent a review copy, and told Darwin that he had "long since, from watching the crossing of domesticated animals and plants, learnt to disbelieve the dogma of the permanence of species." Darwin was delighted that this "celebrated author and divine" had "gradually learnt to see that it is just as noble a conception of the Deity to believe that He created a few original forms capable of self-development into other and needful forms, as to believe that He required a fresh act of creation to supply the voids caused by the action of His laws."While reviews were by custom anonymous, their authors were usually known. Huxley's reviews of On the Origin of Species irritated Owen, whose own anonymous review in April praised himself and his own axiom of the continuous operation of the ordained becoming of living things, took offence at the way the creationist position had been depicted, and complained that his own pre-eminence had been ignored. Owen bitterly attacked Huxley, Hooker and Darwin, but also signalled acceptance of a kind of evolution as a teleological plan in a continuous "ordained becoming", with new species appearing by natural birth.
The dispute between Huxley and Owen over human uniqueness began in public at the 1860 Oxford evolution debate, during a meeting of the British Association for the Advancement of Science in Oxford on Thursday 28 June 1860. After Charles Daubeny's paper "On the Final Causes of the Sexuality of Plants with Particular Reference to Mr. Darwin's Work", the chairman asked Huxley for comments, but he declined as he thought the public venue inappropriate. Owen then spoke of facts which would enable the public to "come to some conclusions ... of the truth of Mr. Darwin's theory", reportedly arguing that "the brain of the gorilla was more different from that of man than from that of the lowest primate particularly because only man had a posterior lobe, a posterior horn, and a hippocampus minor." In response, Huxley flatly but politely "denied altogether that the difference between the brain of the gorilla and man was so great" in a "direct and unqualified contradiction" of Owen, citing previous studies as well as promising to provide detailed support for his position.
Anguish over the death of his son of scarlet fever in September 1860 pushed Huxley to the brink, from which Kingsley rescued him by a series of letters. Huxley put his fury over the death into composing a paper which violently assaulted Owen's ideas and professional reputation. It was published in January 1861 in the first issue of Huxley's relaunched Natural History Review magazine, and presented citations, quotations and letters from leading anatomists to attack Owen's three claims, aiming to prove him "guilty of wilful and deliberate falsehood" by citing Owen himself, and the anatomists whose illustrations Owen had used in the 1857 paper. While readily agreeing that the human brain differed from that of apes in size, proportions and complexity of convolutions, Huxley played the significance of these features down, and argued that to a lesser extent these also differed between the "highest" and "lowest" human races. Darwin congratulated Huxley on this "smasher" against the "canting humbug" Owen. From February to May Huxley delivered a very popular series of sixpenny lectures for working men at the School of Mines where he taught, on "The Relation of Man to the Rest of the Animal Kingdom". He told his wife that "My working men stick by me wonderfully, the house being fuller than ever last night. By next Friday evening they will all be convinced that they are monkeys."
Gorillas became the topic of the day with the return of the explorer Paul Du Chaillu. Owen arranged for him to speak and display his collections on stage at a spectacular Royal Geographical Society meeting on 25 February, and followed this by giving a lecture at the Royal Institution on 19 March on the brains of The Gorilla and the Negro, asserting that the dispute was one of interpretation rather than fact, and hedging his previous claim by stating that humans alone had a hippocampus minor "as defined in human anatomy". This lecture was published in the Athenæum on 23 March with unlabelled and inaccurate illustrations, and Huxley's response in the next issue a week later, Man and the Apes, ridiculed Owen's use of these illustrations and failure to mention the findings of anatomists that the three structures were present in animals. In the following week's issue Owen's letter blamed "the Artist" for the illustrations, but claimed that the argument was correct and referred the reader to his 1858 paper. In the Athenæum of 13 April Huxley responded to this repetition of the claim by writing that "Life is too short to occupy oneself with the slaying of the slain more than once."
Each Saturday, Darwin read the latest ripostes in the Athenæum. Owen tried to smear Huxley by portraying him as an "advocate of man's origins from a transmuted ape", and one of his contributions was titled "Ape-Origin of Man as Tested by the Brain". This backfired, as Huxley had already delighted Darwin by speculating on "pithecoid man", and was glad of the invitation to publicly turn the anatomy of brain structure into a question of human ancestry. Darwin egged him on from Down, writing "Oh Lord what a thorn you must be in the poor dear man's side". Huxley told Darwin's friend Joseph Dalton Hooker, "Owen occupied an entirely untenable position ... The fact is he made a prodigious blunder in commencing the attack, and now his only chance is to be silent and let people forget the exposure. I do not believe that in the whole history of science there is a case of any man of reputation getting himself into such a contemptible position. He will be the laughing-stock of all the continental anatomists."