When Charles Darwin turned his attention to writing about human descent in 1871 he attempted to narrow the fossil gap between human beings and higher primates by presenting persons with intellectual disabilities — "idiots" in the language of the day — as evidence in support of the theory of evolution. This paper explores the four ways that Darwin used persons with intellectual disabilities in The Descent of Man: 1) as intermediate rung on the evolutionary ladder connecting humans and primates; 2) as exemplars of the inevitable waste and loss produced by natural selection acting upon variability; 3) as the floor of a scale representing the "lowest", most unfit variety of any species when individuals were rank ordered by intelligence; and 4) as atavistic reversions to extinct forms whose study would reveal the characteristics of earlier stages of human evolution. Darwin's strategic use of intellectual disability is brought to bear on the controversy regarding the mental state of Darwin's last child.

When Charles Darwin turned his attention to writing about human descent in 1871 he sought to explain the fossil gap between human beings and higher primates. Darwin wished to convince readers that human beings and animals were of common descent and not the result of two separate creations as described in the Bible, however, the fossil evidence, at that time, was less than wholly convincing. No "ape/man" had yet been found that could conclusively prove the common descent of humans and higher primates. Darwin admitted as much, noting "the great break in the organic chain between man and his nearest allies, which cannot be bridged over by an extinct or living species..." (Darwin, 1981(1), 200). Critics, including, to Darwin's chagrin, Alfred Wallace, the co-discoverer of the theory of natural selection, believed that evolution could not explain the special case of human development. As early as 1841 they had thrown down the gauntlet by asking evolutionists to produce "a talking race of monkeys, or a mute race of men" (Taylor 1841, 19). Darwin addressed the problem in three ways. First, he noted, quite reasonably, that the recovery of fossils had only just begun and that many remote areas had yet to be explored; the fossil gap might yet be bridged by future finds. Secondly, he attempted to show that the gap in living forms was a predictable consequence of evolution due to the extinction of intermediate species through natural selection. To illustrate, he suggested that: At some future period, not very distant as measured by centuries, the civilized races of man will almost certainly exterminate and replace throughout the world the savage races. At the same time the anthropomorphous apes…will no doubt be exterminated. The break will then be rendered wider, for it will intervene between man in a more civilized state, as we may hope than the Caucasian, and some ape as low as a baboon, instead of as at present between the negro or Australian [aborigines] and the gorilla. (Darwin, 1981(1), 201) Darwin's third strategy, and the subject of this paper, was to claim that, although no "missing link" fossil had yet been discovered, actual living forms, intermediate between apes and the "civilized races" existed. These were "idiots" and "savages" (Stepan, 1982). This paper describes how Darwin used intellectual disabilities to support the theory of evolution, and, in so doing, facilitated a reliance on heredity as definitive of persons with disabilities along with the view that they were not wholly human. It shows that the careful observations and circumspect reasoning that characterized Darwin's work on pigeons, worms and barnacles were not evident when he focused on the condition in human beings that he and his contemporaries called "idiocy." Finally, it discusses Darwin's relationship with his last child, who many believed suffered from mental retardation, in light of his scientific descriptions of intellectual disability.

Reframing Animals and Humans To convince readers that evolution explained human as well as animal origins, Darwin needed to raise the public's estimation of animals' capacities while simultaneously lowering their regard for human beings. Variation lay at the heart of the theory of natural selection: vigorous organisms survived and propagated while the weak or "unfit" were eliminated. Darwin's strategy was to seek out the highest examples he could find of animal functioning and present these against the lowest of humans. In arguing that "Animals manifestly enjoy excitement and suffer from ennui…[and that] all animals feel Wonder, and many exhibit Curiosity" (Darwin, 1981(1), 42) he aimed to show that there existed an overlap between the most highly evolved animals, and the least developed human beings. Thus, Darwin found much to praise in animals and much to condemn in humans. He was at pains to discredit the belief, most famously articulated by Rousseau, that the life of natural man was noble. In fact, claimed Darwin, "the greatest intemperance with savages is no reproach. Their utter licentiousness, not to mention unnatural crimes, is something astounding" (Darwin, 1981(1), 96). Moreover, "most savages are utterly indifferent to the sufferings of strangers, or even delight in witnessing them…Some savages take a horrid pleasure in cruelty to animals and humanity with them is an unknown virtue" (94). While they might show kindness to one another they seldom extended it to strangers. According to Darwin the admonition to "never, never trust an Indian" was justified (95). At the same time, Darwin praised social animals that provided services to one another and appeared to demonstrate love. He narrated tales of animal heroism including that of a monkey who rescued a zoo keeper from an attack by a much larger and stronger animal, and a baboon who rescued an infant from a threatening pack of dogs. Darwin lauded dogs for their sense of "conscience", their loyalty and self-command and suggested that they had more self-awareness than some non-Europeans: Can we feel sure that an old dog with an excellent memory and some power of imagination, as shewn (sic) by his dreams, never reflects on his past pleasures in the chase? And this would be a form of self-consciousness. On the other hand… how little can the hard-worked wife of a degraded Australian savage, who uses hardly any abstract words and cannot count above four exert her self-consciousness or reflect on the nature of her own existence. (Darwin, 1981(1), 62) If non-Europeans came off badly in The Descent, those with intellectual disabilities came off worse. In order to make his point, Darwin sought to link them with an animal essence outside (and below) the boundary of humanity. While this portrait would ultimately serve to draw a great deal of attention to the condition of people with intellectual disabilities, it ensured that the attention would be focused on their putative differences from others rather than their commonalities. Darwin was not the first to suggest that the study of intellectual disabilities might be a key to the study of human descent. In 1864, the radically anti-clerical German anthropologist Carl Vogt had argued that "when the normal form leaves us in the lurch as regards our investigations, we have a right to avail ourselves of abnormal forms, where we may reap a rich harvest...microcephali and born idiots present as perfect a series from man to the ape as may be wished for" (Vogt 1864, 194-195). Multiple citations to Vogt's work on idiots and savages are found in The Descent. Three years before publication of The Descent, J. P. Lesley (1868) developed Vogt's contention that evidence of human evolution need not rest on the discovery of tribes of ape/men, since "developmentally arrested" people, in all societies, made the case: Individuals scattered all over the world, through all the human races, with low foreheads, small brains, long arms, thin legs, projecting, tusk-like teeth, suppressed noses, and other marks of arrested development; to say nothing of millions of idiots and cretins produced by the same arrest in every generation of mankind, sustain the argument. (120) Following this logic, Darwin used the existence of intellectual disability to support the theory of human evolution in four ways. In The Descent "idiots" were presented as: (1) an intermediate rung on the evolutionary ladder connecting humans and primates; (2) exemplars of the inevitable waste and loss produced by natural selection acting upon variability; (3) the floor of a scale representing the "lowest", most unfit variety of any species when individuals were rank ordered by intelligence; and (4) atavistic reversions to extinct forms whose study would reveal the characteristics of earlier stages of human evolution.

Intermediate Rung on the Evolutionary Ladder In assigning to "idiots" a place between the "lowest" human races and apes, Darwin and others used them — along with a racial hierarchy — to link animals and humans. Vogt's observations were crucial in this regard. He had examined the physique of "idiots" and claimed to have discovered that, "the arms seem disproportionately long, the legs short and weak ...We need only place the skulls of the Negro, chimpanzee and idiot side by side, to show that the idiot holds in every respect an intermediate place between them" (Vogt 1864, 197-198). Darwin cited Vogt as authority for his passage in the 1874 (second edition) of The Descent that idiots are strong and remarkably active, continually gambolling and jumping about, and making grimaces. They often ascend stairs on all fours; are curiously fond of climbing up furniture or trees...Idiots also resemble the lower animals in some other respects; thus several cases are recorded of their carefully smelling every mouthful of food before eating it. One idiot is described as often using his mouth in aid of his hands while hunting for lice. They are often filthy in their habits, and have no sense of decency; and several cases have been published of their bodies being remarkably hairy. (1874, 40-41) The claim that idiots sometimes walked on all fours is significant because Darwin believed that bi-pedalism was unique to humanity and, in developmental history, the point at which human development took a divergent path from animal evolution (Landau, 1991). Going on all fours made the intellectually disabled more animal than human. In the same vein, Vogt (1864) had argued that the idiot who has remained stationary in a primary stage, stands nearer to the ape than to his progenitor. The distance which his brain has to pass to perfect human development is greater than the distance it has passed from the simian stage (170) In contrast, Richard Owens had argued, in 1835, that the skull of a person with intellectual disabilities was human in every way. According to Owen these were not developmentally arrested primates, but incompletely developed human beings (Desmond, 1989). Owens, it will be recalled, was a prominent opponent of the theory of evolution and in the late nineteenth century Darwin and followers had reason to define disability differently.

Profligate Nature's Waste At the heart of the theory of natural selection was the idea that life was a competitive struggle that resulted in the wholesale destruction of the unfit, losers in the struggle to survive. Darwin believed that humans competed against one another rather than against animals. The existence of persons with intellectual disabilities provided for him a contemporary example of the process by which the weak were culled from a population to strengthen the strong. The idiot became an exemplar of the organism marked by selection for extinction. If left alone, as nature's waste or "elimination", they would swiftly perish: "With savages, the weak in body or mind are soon eliminated; and those that survive commonly exhibit a vigorous state of health" Darwin, 1871(1), 168). On the other hand, Darwin argued, societies that support the weak do at their own risk: We civilized men…do our utmost to check the process of elimination; we build asylums for the imbecile, the maimed, and the sick…Thus the weak members of civilized societies propagate their kind. No one who has attended to the breeding of domestic animals will doubt that this must be highly injurious to the race of man. It is surprising how soon a want of care, or care wrongly directed, leads to the degeneration of a domestic race; but excepting in the case of man himself, hardly any one is so ignorant as to allow his worst animals to breed" (168). Nonetheless, Darwin believed societies should tolerate the survival of the weak because compassion was one of humanity's finest and most developed qualities. At the same time he hoped, but doubted, that "the weaker and inferior members of society" (I, 169) might refrain from marrying and bearing offspring as often as the strong. In this regard, he cited the work of his cousin Francis Galton, Hereditary Genius (1965), which had recently introduced the concept of eugenics. Darwin (1874) cautioned that if society did not "prevent the reckless, the vicious and otherwise inferior members of society from increasing at a quicker rate than the better class of men, the nation will retrograde, as has too often occurred in the history of the world" (159). Yet Darwin's views in this area were complex. In 1877 he did not lend his support to the two publishers of a pamphlet on birth control who were being tried in London for obscenity. They hoped Darwin would lend scientific support to their cause since his work had broached the topic of limiting procreation. However, Darwin refused to testify in their favor and threatened to denounce them if he was subjected to a subpoena. Moreover, he announced that he was opposed to any "artificial means of preventing conception" (quoted in Desmond and Morris, 1994, 627). Nonetheless, Darwin's view that it would be to humanity's benefit to discourage the reproduction of the less intelligent had lasting influence. By 1900 experts agreed that total institutionalization was the necessary treatment for the "feebleminded." When the eugenics movement reached high crest after 1910 doctors and psychologists working in the area of intellectual disabilities became committed to eliminating the condition through involuntary sterilization and custodial isolation (Kevles, 1985; Trent, 1994).

Floor of a Scale Darwin and his circle viewed intelligence as the most crucial element in human selection. This led to an interest in how individuals within and between species compared on this attribute. Remarkably, Darwin presented human intellectual disability as the floor of a scale to represent the lowest state of any species. The first edition of The Descent included the remarkable claim that "we may trace a perfect gradation from the mind of an utter idiot, lower than that of the lowest animal, to the mind of a Newton" (Darwin, 1981(1), 106, emphasis added). That Darwin, who had studied barnacles and worms, could claim that any human being might be less intelligent than "the lowest animal", illustrates how low the standing of persons with intellectual disabilities had fallen in the light of evolution theory. Given Darwin's well deserved reputation for thorough analysis of data and cautious presentation of conclusions, the statement is a rare example of hyperbole. In the second edition of The Descent Darwin modulated the statement to "lower than that of an animal low in the scale" (Darwin, 1874, 143). Reversion to an Ancestral Form Darwin did much to stimulate scientific interest in the field of intellectual disabilities by stating that persons with the condition could be studied as regressions or atavisms to earlier stages of human development. As noted, the strategy was aimed at critics who found support for human evolution lacking. If persons with intellectual disabilities were living fossils they could provide a window on the human past. Darwin (1981) explained that "whenever a structure is arrested in its development, but still continues growing until it closely resembles a corresponding structure in some lower and adult member of the same group, we may in one sense consider it a case of reversion. The lower members in a group give us some idea how the common progenitor of the group was probably constructed" (I, 122). In the Descent's second edition Darwin (1874) added the claim that "idiots are often very hairy, and they are apt to revert in other characters to a lower animal type" (687). Since primates have more hair than humans, idiots' supposedly hirsute state was explained as a reversion. Darwin stated that "the early progenitors of man were no doubt once covered with hair, both sexes having beards" (1871, I, 206). He also believed that the structure of the brain in persons with microcephaly was a reversion (Darwin, 1871). In this fashion, Darwin and other evolutionists, recast persons with intellectual disabilities into a class whose animal essence placed them outside the human pale. Their usefulness as evolutionary evidence was illustrated by the teaching props that Darwin's protégé, Georges Romanes, used in an 1878 talk on the evolution of intelligence to the British Association for the Advancement of Science. The London Times reported that he displayed "savages, young children, idiots, and uneducated deaf-mutes" to show that "man and brute have much more in common intellectually, and perhaps, even, than is dreamt of" (quoted in Desmond and Moore, 1994, 633). The sensational presentation made a powerful impact on the audience which accorded Romanes the ultimate honor at a scientific meeting, a standing ovation. Afterward, Darwin, in jest, wrote to Romanes that "Frank [Darwin's son] says you ought to keep an idiot, a deaf mute, a monkey, and a baby in your house" (633). Other scientists elaborated the link between animals and intellectual disabilities. Soon after the publication of The Descent, Henry Maudsley (1873) described an "animal type of brain in idiocy" which appeared together with "remarkable animal traits and instincts "(47). He claimed there was an "ape-faced idiot" in Scotland who "grins, chatters, and screams like a monkey" (48). More incredibly, he described a woman with intellectual disabilities whose appearance and behavior resembled that of a goose. According to Maudsley, the lower part of her face resembled a bill and her neck was so long and elastic that she could turn around with it and touch her back. The angles of her shoulder-blades stood out and when she moved her arms they appeared to be rudimentary wings. The lower part of her face had "a somewhat bill-like appearance" (50). The woman cackled like a goose, showed anger by flapping her arms, loved the bath, but "screeched" (51) when removed from the water. Darwin cited Maudsley's descriptions of "various strange animal-like traits in idiots" in his 1872 work The Expression of the Emotions in Man and Animals as evidence of their "brute nature" (Darwin, 1965, 244). In the same work, Darwin included another secondary report of an "epileptic idiot" with a fearsome, animal like disposition and appearance: When anyone touches his toys, he slowly raised his head from its habitual downward position, and fixes his eyes on the offender, with a tardy yet angry scowl. If the annoyance be repeated he draws back his thick lips and reveals a prominent row of hideous fangs (large canines being especially noticeable) and then makes a quick and cruel clutch with his open hand at the offending person. (243) When Darwin focused his attention on the expression of emotions in humans and animals he included reports on idiots because he believed that, being at a lower stage of development, they were more passionate and therefore easier to study than normal adults whose emotional displays were less frequent and intense. After declaring that "with idiots laughter is the most prevalent and frequent of all the emotional expressions" (Darwin, 1965, 197), Darwin distinguished between those who laughed frequently but senselessly, those whose "stereotyped smile" and frequent laughter was an expression of a persistently joyous state, and those who were "morose" and never laughed. In these extreme characterizations idiots were either flooded with emotion or completely without it. If "born idiotic" they cried, but if cretins they did not (Darwin, 1965, 155).

Charles Waring Darwin In spite of these and other negative associations there has been speculation among historians that the last of Darwin's ten children, Charles Waring, who died at about 19 months of age, was born with severe mental intellectual disability (Bizzo, 1992, Bowlby, 1990, Desmond & Moore, 1991, Keynes, 2001, Smith, 1999, White & Gribben, 1995). The evidence for this has been adduced from the circumstances of the child's birth — Emma Darwin was 48 when she gave birth in 1856 — and a passage from a letter written by older daughter Henrietta that stated that the poor little baby was born without its full share of intelligence. Both my father and mother were infinitely tender towards him, but, when he died in the summer of 1858, after their first sorrow, they could only feel thankful. He had never learnt to walk or talk. (Litchfield, 1915, 162) Keynes (2001) showed a picture of the baby to an unnamed pediatrician who stated that the child's features were consistent with Down syndrome. On the other hand, the author of the most definitive Darwin biography, Janet Browne (2002), concluded that there is no compelling evidence of the infant having a significant intellectual disability. She suggested that Charles Waring might have been "slightly" delayed as a result of exposure to mercury, a common ingredient in medicines of the time. According to Browne, Henrietta's description "probably underestimated both the love that Emma and Charles felt for him and his mental capacities" (37). The most complete and compelling description of baby Charles was penned by Darwin himself, shortly after the baby's death. This affectionate and loving tribute contains evidence for both views of the baby's mental status. While Darwin noted that the baby Charles "was small for his age & backward in walking & talking" he also labeled him "intelligent & observant" (Burkhardt and Smith, 1991, 521). The latter must be taken as more than casual testimony. Darwin's years of biological field work had made him an astute and analytic observer. Moreover, he was also a pioneer in the study of infant development, having begun, in 1839, a clinical notebook of his child Willy that anticipated Piaget's seminal work with his children in the next century (Keynes, 2001). Other observations of Darwin are suggestive of an intellectual disability, but ultimately inconclusive. Darwin did not provide evidence to refute Henrietta's much later claim that the baby never learned to walk or talk, but his failure to discuss these milestones may have been purely incidental. He was not aware that historians would, in the future, evaluate every word of his memorial for clues about his baby's status. On the other hand, the details he did provide suggested a baby younger than 19 months of age, who grimaced and made "nice little bubbling noises" (Burkhart and Smith, 521) but did not speak words or move from place to place on his own. Nevertheless, the memorial makes clear that Darwin considered his infant son fully human. His tender description is of a whole different order than his writing on intellectual disability in support of the theory of evolution. In this, Smith (1999) saw "a testament to the value of a child with mental retardation to his family" (505). While this may be so, it is unlikely that Darwin realized it. We have no evidence that Darwin ever made a connection between his last son's "backward" development and the animalistic "idiots" he described in The Descent.