Categories and boundaries have long obsessed students of the natural world. The organization of information about animals, plants, and minerals into a coherent system was part of the core disciplinary or protodisciplinary agenda of eighteenth and nineteenth-century naturalists. On the most practical level, system was necessary for purposes of retrieval and comparison, as knowledge about the world and its contents expanded exponentially during the centuries of European exploration and expansion. More abstractly, especially in the wake of Newton, taxonomy constituted a vital component of naturalists’ claim to intellectual respectability and prestige. Without system, they feared, natural history would be “but a confused, undisciplined crowd of subjects” and naturalists “mere collectors of curiosities and superficial trifles…, objects of ridicule rather than respect.”
Before any natural kind could be assigned its place in a system, its limits had to be ascertained. That is, it had to be described with sufficient precision to make clear which individuals it included and which it excluded. This was often easier said than done. Numerous concrete obstacles to producing accurate and comprehensive descriptions existed at a period when transportation was slow and uncertain, communication among specialists was difficult, and preservation techniques were often ineffective. In addition, although some organisms, like the giraffe, can be easily differentiated from all others, many plants and animals have relatives close enough to undermine the distinction between similarity and sameness. Additional study did not necessarily make things clearer; indeed, intensified examination of dubious cases often made them seem more difficult to describe and delimit. As Charles Darwin observed in relation to the differentiation of species and varieties, “it is in the best-known countries that we find the greatest number of forms of doubtful value. …if any animal or plant…closely attract [human] attention, varieties…will almost universally be found recorded.” Human beings fit both criteria. The territories where they lived were inevitably very familiar and well-documented, and most people found them (that is, themselves) to be the most fascinating of the earth’s inhabitants.
Consequently many naturalists struggled to determine where people fit in the natural order. One possibility—the one implied by the OED definitions, as well as by the chain of being that had descended from antiquity—was that humans occupied a position just outside or on top of it. But other possibilities existed, and they suggested greater integration. As the gap between humans and other creatures diminished, the possibility of boundary confusion increased. Many naturalists followed the lead of Linnaeus, the Swedish taxonomist whose system of latinate binomials remains the foundation of botanical and zoological nomenclature. Unlike many of his contemporaries, he had no doubt that people were a kind of animal, if an unusual kind. He embedded humans firmly within his taxonomic system, devising the primate order to accommodate four genera: Homo, Simia (monkeys and apes), Lemur (prosimians), and Vespertilio (bats). He did not, however, treat humans and their ilk in quite the same way as he treated these structurally parallel categories. Instead, he signaled human distinctiveness in the brief characterizations that accompanied his schematic list of genera. For simians and prosimians he highlighted dentition, and for bats, wings; with regard to Homo he identified no distinctive physical feature, but merely commented “nosce te ipsum” (know thyself).
This very terse description left many questions unanswered, the most obvious of which was how to define “thyself.” And at the next level of analysis, where he described each genus in greater detail and itemized its constituent species, Linnaeus offered some very suggestive answers. In his classification, Homo was not a monolithic taxon. It contained two species, of which Homo sapiens, the first and largest, was further subdivided into the conventional geographical races (American, European, Asiatic, and African), with additional categories for the wild children who occasionally turned up (Ferus) and for still more unusual kinds of people (Monstrosus). According to Linnaeus’ descriptions, they all differed sufficiently in their physical and temperamental qualities to make it unlikely that the self-knowledge of members of one group, however comprehensive and accurate, would automatically illuminate the nature of the others. For example, Homo Europaeus was “sanguineus,” while Homo Afer was “phlegmaticus.” The other species within the genus Homo more severely challenged the limits of empathetic insight. Linnaeus’ correspondence and his lectures at Uppsala University contained repeated suggestions that he found it difficult to establish a firm dividing line between humans and apes. Homo troglodytes was not subdivided; its sole occupant was the orangutan.
The evidence offered by this placement is ambiguous, however. The orangutan was also known as Homo sylvestris or the wild man of the woods (a translation from Malay, although not of the Malay word for the orangutan), and, at a time when the unity of the human species was the subject of vigorous debate, there was widespread uncertainty about whether or not orangutans were human. In addition, naturalists had not yet clearly distinguished the orangutan of southeast Asia from the chimpanzee of Africa, about whose taxonomic placement there was, therefore, similar (or identical) uncertainty. In 1699, for example, the anatomist Edward Tyson had published a treatise entitled Orang-Outang, sive Homo Sylvestris. Or the Anatomy of a Pygmie compared with that of a Monkey, an Ape and a Man. By “ape” he meant baboon, and by “pygmie” he meant “chimpanzee.” The human status of the quasi-mythical pygmies had, conversely, long been the subject of European speculation. Even at the end of the eighteenth century, naturalists could claim that the “race of men of diminutive stature” or “supposed nation of pygmies” described by the ancients, was “nothing more than a species of apes…that resemble us but very imperfectly.”
Despite Linnaeus’s iconic status as a systematizer, in his own time as well as subsequently, his inclusive primate order was frequently rejected. Not everyone, whether a serious naturalist or a casual observer of nature, enjoyed being placed firmly within the animal kingdom, even at the head of it; the closer juxtaposition within the genus Homo was inevitably even more troubling. According to the British naturalist Thomas Pennant, “my vanity will not suffer me to rank mankind with Apes, Monkies, Maucaucos, and Bats”; a colleague further asserted that “we may perhaps be pardoned for the repugnance we feel to place the monkey at the head of the brute creation, and thus to associate him…with man.” Such reluctance occasionally moved dissenters to propose alternative taxonomies that implicitly posited a much wider separation. Thus early in the nineteenth century the anatomist William Lawrence suggested that “the principles must be incorrect, which lead to such an approximation” (that is, between humans, apes, and monkeys within the primate order); instead, he argued that “the peculiar characteristics of man appear to me so very strong, that I not only deem him a distinct species, but also…a separate order.”
Nevertheless, such assertions were rearguard efforts and, at least among specialists, Linnaeus’s primate order ultimately triumphed. By the middle of the nineteenth century most zoologists had accepted it. In non-specialist understandings, the possibility that apes might actually be people lingered in various ways. The illustrations in books of popular natural history often portrayed apes as particularly human in both appearance and behavior, showing them assuming erect posture, using human tools (frequently a walking stick), and approximating human proportions in the torso and limbs. This visual tradition was not confined to the page or the canvas. It was constantly reenacted by the chimpanzees and orangutans who inhabited nineteenth-century zoos and menageries. Show apes ate with table utensils, sipped tea from cups, and slept under blankets. One orangutan who lived in London’s Exeter Change Menagerie amused herself by carefully turning the pages of an illustrated book. At the Regent’s Park Zoo a chimpanzee named Jenny regularly appeared in a flannel nightgown and robe. Consul, a young chimpanzee who lived in Manchester’s Belle Vue Zoological Gardens, greeted the public dressed in a jacket and straw hat, smoked cigarettes, and drank his liquor from a glass.
In addition, rumor persistently whispered that these visual analogies might represent more substantial and productive connections. Thus one seventeenth-century report featured a “poor miserable fellow” who had copulated with a monkey “not out of any evil intention…, but only to procreat a Monster, with which he might win his bread.” At the end of the eighteenth century the surgeon and naturalist Charles White reported that orangutans “have been known to carry off negro-boys, girls and even women…as objects of brutal passion.” In his pioneering account of chimpanzee anatomy, Edward Tyson had gone out of his way to assure his readers that “notwithstanding our Pygmie does so much resemble a Man…: yet by no means do I look upon it as the Product of a mixt generation.”
Some claims were less restrained, or more enthusiastic. For example, a Victorian impresario advertised the merely hairy Julia Pastrana as “a hybrid, wherein the nature of woman predominates over the ourang-outangs.” And there were other ways of positing similarly concrete connections between people and the non-human animals most nearly allied to them by anatomy. Well into the nineteenth century, physicians explained many kinds of birth defects as the unfortunate consequences of what was termed maternal imagination or impression– a kind of mental hybridization. Thus in 1867 the Lancet attributed the dense fur covering an unfortunate girl’s back to the fact that her mother had been frightened by an organ grinder’s monkey. The rhetoric of evolution could be deployed to suggest that human-ape intermediaries existed in the present, as well as in the ancestral past. For example, a Laotian girl named Krao was exhibited in 1883 as “Darwin’s missing link,” because she was unusually hairy, and because she allegedly possessed prehensile feet and could pout like a chimpanzee.
Among scientists, the conviction that apes were not people did not exclude the possibility that some people might be apes. Indeed, over the course of the nineteenth century this possibility loomed increasingly large, as specialists focused more intensely on ways to subdivide the human species. The stakes could be high, both intellectually and politically. During the 1860s, the nascent British anthropological community was riven by a struggle between so-called “ethnologicals,” generally monogenists (believers in the common descent of all human varieties), and the “anthropologicals,” generally polygenists (believers in the independent origin of human varieties). In the presidential address that inaugurated the Anthropological Society of London in 1863, which was billed as a consideration of “the station to be assigned to [the Negro] in the genus Homo,” James Hunt argued that “there is as good a reason for classifying the Negro as a distinct species from the European, as…for making the ass a distinct species from the zebra.” After a series of disparaging characterizations, Hunt concluded that “the Negro race can only be humanised and civilised by Europeans.”
As displays of great apes suggested their latent humanity, the anthropoid qualities of derogated human groups could be mapped concretely as well as in words. Museums frequently exhibited the remains of non-European humans in ways that underlined their difference from Europeans, or suggested their greater affinity with other animals. Thus in 1766 a travelling collection of “curiosities” grouped a “Negro Child” with a “Monstrous Cat with 8 legs,” a “Chicken’s Foot with 6 Toes,” a sloth, and an armadillo; a century later the Cambridge University anatomical collection listed separate entries for the “Tegumentary System or Skin” of the “Human” and the “Negro.” If twentieth-century natural history museums included displays of human artifacts, or dioramas showing human activity, they were much more likely to feature people who could be characterized as exotic or primitive, than people wearing business suits and carrying briefcases.
Human uniqueness has come under increasing taxonomic challenge. The phylogenetic relationship between people and the other great apes has also become better and better documented, so that it is now generally recognized that a classification that groups chimpanzees, gorillas, and orangutans together, and leaves humans in splendid isolation, is based primarily on wishful thinking. Although the fine points of ape taxonomy are still subject to debate, it has become clear that orangutans rather than humans are the outliers. And if the claim embodied in the title of Jared Diamond’s The Third Chimpanzee might still seem provocative, a more generic version of it is definitely ready for prime time. A publicity release for a Nova television program entitled “Ape Genius” begins, “Congratulations: You are an ape.” I have visited zoos that provide a mirror in which visitors can admire one last specimen as they leave the great ape house.
This increasing convergence has destabilized the assumptions on which the dictionary definitions of “human” and “humanist” have been based. If people are apes, then they must understand and justify their pre-eminence in novel ways, or, if they are committed to traditional understandings of human distinctiveness, they must at least find novel evidence to support them. As the evidence of physical difference has become less persuasive, evidence from the behavioral, intellectual or spiritual sphere has gained prominence. Nineteenth-century naturalists uneasy about the human-ape connection frequently posited an alternative alliance. They reasoned that if non-primate animals resembled humans more closely than apes, then they would necessarily displace apes from their awkward proximity. In 1881, for example, George J. Romanes, a close friend and colleague of Darwin’s with a special interest in animal behavior, celebrated the “high intelligence” and “gregarious instincts” of the dog, which, he claimed, gave it a more “massive as well as more complex” psychology than any member of the monkey family. And since the competing closeness so constructed was clearly figurative, the whole animal creation was thereby implicitly removed to a more comfortable distance.
Temperament, of course, is hard to pin down; as with Linnaeus’ characterization of human types, it is often in the eye of the beholder. And the more that we have come to know about the dispositions of chimpanzees and other primates, the harder it has become to maintain a firm separation. Many characteristics that once seemed exclusively or at least distinctively human, including moral intuition, oppressive patriarchy, internecine strife, and cannibalism, turn out to be more widely distributed. Intelligence has proved a weak reed for similar reasons. None of the intellectual barriers erected to isolate people have proved reliably robust. In Sartor Resartus Thomas Carlyle chose “Tool-using Animal” as a definition that emphasized human uniqueness, noting that “Man is called a Laughing Animal, but do not the apes also laugh, or attempt to do it.” In the wake of Jane Goodall’s pioneering observations of chimpanzees, tool creation has been observed in several primate species (many kinds of animals are capable of using found tools). The obstacles to speech in other primates are located in their vocal tracts rather than in their brains. In any case, parrots can talk, as can a few other kinds of birds; some of them, like the recently deceased Alex, arguably make sense. With the aid of sign language, computers, or other accessories, apes and dolphins can breach the final barrier, that of symbolic communication.
The implications of these snowballing recognitions are not just abstract or theoretical. In the preface to The Great Ape Project, the editors argue that the “sphere of moral equality” to which we all belong should be based not on reductive taxonomy—membership in the species Homo sapiens—but on “the fact that we are intelligent beings with a rich and varied social and emotional life.” Since these “are qualities that we share…with our fellow great apes,” the boundary of the sphere should be redrawn so that they are included too. Contributors include scientists who study apes in the wild, scientists who study apes in captivity, and specialists in language, philosophy, and law, among other things. They all subscribe to the “Declaration on Great Apes,” which specifies that for human beings, chimpanzees, gorillas, and orangutans, the right to life, the protection of individual liberty, and the prohibition of torture should all be enforceable by law.
Since not all humans enjoy these legal protections, it is not surprising that apes remain outside the “sphere of moral equality.” Some recent developments in Europe suggest the possibility of future change, especially the resolution adopted in 2008 by a committee of the Spanish parliament, giving great apes the rights formulated in The Great Ape Project. But such change will certainly be slow, and in any case most apes do not live in Europe, at least not yet. These developments reflect the evolution of an argument that has been going on for centuries. In comparison, most humanists have just begun to wonder about the limits and limitations of the human. We might, indeed, wonder whether the label “humanist” has always carried a certain amount of hubris (or at least tunnel vision), as well as what it would take to become “post-human.” Perhaps the liberation of all the apes now held in captivity, not to speak of all the other animals.
 Entry for “human,” Oxford English Dictionary Online (Oxford University Press, 2008).
 Entry for “humanist,” OED.
 William Borlase, Natural History of Cornwall (Oxford: W. Jackson, 1768), viii; Richard Pulteney, A General View of the Writings of Linnaeus (London: J. Mawman, 1805), 11.
 Charles Darwin, On the Origin of Species, ed. Ernst Mayr (1859; Cambridge, MA: Harvard University Press, 1964), 50.
 Harriet Ritvo, The Platypus and the Mermaid, and Other Figments of the Classifying Imagination (Cambridge, MA: Harvard University Press, 1997), 23, 28-31.
 Carolus Linnaeus, Systema Naturae: Regnum Animale (1758; London: British Museum (Natural History), 1956), 18.
 Linnaeus, Systema Naturae, 20-23.
 Lisbet Koerner, Linnaeus: Nature and Nation (Cambridge, Ma.: Harvard University Press, 1999), 87-88.
 Linnaeus, Systema Naturae, 24.
. Edward Tyson, Orang-Outang, sive Homo Sylvestris. Or, the Anatomy of a Pygmie compared with that of a Monkey, an Ape, and a Man (London: Thomas Bennet, 1699), “Preface” n.p.
. An Historical Miscellany of the Curiosities and Rarities in Nature and Art… (London: Champante and Whitrow, ca. 1800), III, 288-89.
. Thomas Pennant, History of Quadrupeds (London: B. and J. White, 1793), iv; William Wood, Zoography; or the Beauties of Nature Displayed (London: Cadell and Davies, 1807), xvii.
. William Lawrence, Lectures on Comparative Anatomy, Physiology, Zoology, and the Natural History of Man; delivered at the Royal College of Surgeons in the Years 1816, 1817, and 1818 (London: R. Carlile, 1823), 127, 131.
 See, for example the illustrations in Thomas Bewick’s popular General History of Quadrupeds, first published in 1790.
. C. V. A. Peel, The Zoological Gardens of Europe: Their History and Chief Features (London: F. E. Robinson, 1903), 205-206; “In Memory of Consul,” pamphlet in the Belle Vue collection, Chetham’s Library, Manchester.
. Quoted in Dudley Wilson, Signs and Portents: Monstrous Births from the Middle Ages to the Enlightenment (Routledge: London, 1991), 56-67.
 Charles White, An Account of the Regular Gradation in Man, and in Different Animals and Vegetables: and from the Former to the Latter (London: C. Dilly, 1799), 34.
. Tyson, Orang-Outang, 2.
. Jan Bondeson and A. E. W. Miles, “Julia Pastrana, the Nondescript: An Example of Congenital Generalized Hypertrichosis Terminalis with Gingival Hyperplasia,” American Journal of Medical Genetics 47 (1993), 199.
 Lancet, 1867.
. Nature 12 May 1882, cited in Martin Howard, Victorian Grotesque: An Illustrated Excursion into Medical Curiosities, Freaks and Abnormalities–Principally of the Victorian Age (London: Jupiter Books, 1977), 56-57.
 Stocking, Victorian Anthropology, 248-254; for the subsequent evolution of this debate, see Douglas Lorimer, “Theoretical Racism in Late-Victorian Anthropology, 1870-1900,” Victorian Studies 31 (1988), 405-430.
 James Hunt, “On the Negro’s Place in Nature,” Memoirs Read before the Anthropological Society of London 1 (1863-64), 1, 51-52.
 Catalogue of a Great Variety of Natural and Artificial Curiosities, Now Exhibiting at the Large House, the Corner of Queen’s Row, facing the Road, at Pimlico (London, 1766), 4; G. M. Humphrey, Analysis of the Physiological Series in the Gallery of the Museum of Comparative Anatomy (Cambridge, 1866), 9.
 Jared Diamond, The Third Chimpanzee: The Evolution and Future of the Human Animal (New York: HarperCollins, 1992).
. George J. Romanes, Animal Intelligence (New York: D. Appleton, 1896), 439.
 See, for example, Frans De Waal, Good Natured: The Origins of Right and Wrong in Humans and Other Animals (Cambridge, Ma.: Harvard University Press, 1996) and Richard Wrangham and Dale Peterson, Demonic Males: Apes and the Origins of Human Violence (Boston: Houghton Mifflin, 1996).
 Thomas Carlyle, Sartor Resartus (1836; London: J. M. Dent, 1908), 30.
 Jane Goodall, In the Shadow of Man (rev. ed. Boston: Houghton Mifflin, 1988), 277-80.
 Diamond, Third Chimpanzee, 55.
 Irene Pepperberg, The Alex Studies: Cognitive and Communicative Abilities of Gray Parrots (Cambridge, Ma.: Harvard University Press, 2002).
 Donald Griffin, Animal Minds: Beyond Cognition to Consciousness (Chicago: University of Chicago Press, 2001), 228-51.
 Paola Cavalieri and Peter Singer, eds., The Great Ape Project: Equality Beyond Humanity (New York: St. Martin’s Press, 1994), 1.
 Cavalieri and Singer, Great Ape Project, 4-6.
 Jeffrey Stinson, “Activists pursue basic legal rights for great apes; Spain first to vote on some freedoms,” USA Today (July 15, 2008), 7A. (Accessed on Lexis-Nexis)