Profoundly Intellectually Disabled Humans and the Great Apes: A Comparison
In PAOLA CAVALIERI & PETER SINGER (eds.), The Great Ape Project
New York: St. Martin's Griffin, 1993, pp. 159-172
Equality and Intellectually Disabled People
If we make a serious effort to understand the idea of equality we find that even in our modern, enlightened world some consequences of this principle are overlooked. In this chapter I argue that the development of this idea, which did not reach intellectually disabled people until the early 1970s (when two declarations of the United Nations were passed) is still not complete. I shall try to show that opposition to discrimination against intellectually disabled people is based on principles that lead to opposition to discrimination against other sentient beings who are also unable to defend their own interests.
The history of this idea of equality can be seen as a story of the development of the moral requirement to give up unjustified forms of discrimination. The great variety of living beings on our planet has given rise to many possible forms of discrimination by beings who could take advantage of these differences. Article 2 of the 1948 United Nations Declaration of Human Rights refers to a number of past forms of discrimination. It rejects 'distinctions of any kind, such as race, colour, sex, language, religion, political or other opinion, national or social origin, property, birth or other status'. Although it cannot be denied that all over the world people violate the idea of equality, we cannot ignore the progress of this idea. As evidence of this, one could point to recently passed German regulations regarding the appointment of women to public offices, or to the most recent developments in South Africa in which the policy of apartheid has finally been abandoned.
The idea of equality is constantly being refined. One hundred and fifty years ago, Harriet Taylor Mill described the essence of this idea in an article about the enfranchisement of women: 'It is an acknowledged dictate of justice to make no degrading distinctions without necessity. In all things the presumption ought to be on the side of equality.' In the second part of the present century the idea of equality gained another important victory on behalf of a so far neglected minority. This victory was also significant for its practical consequences. In contrast to women or racial minorities, this minority is not always able to stand up for its rights. The fourth congress of the International League of Societies for Persons with Mental Handicap (ILSMH) met in October 1968 in Jerusalem and agreed to a 'Declaration on the General and Special Rights of Mentally Retarded Persons'. Representatives from thirty-four countries participated in this decision. The declaration was taken up, discussed and finally accepted by the United Nations. The General Assembly unanimously accepted Resolution No. 2856 (XXVI): 'Declaration on the Rights of Mentally Retarded Persons'. Article 1 expresses the principal basis of the declaration, namely that 'the mentally retarded person has . . . the same rights as other human beings'. Articles 2 to 7 state rights to medical care and educational training, to live in one's own family and to participate in community living. They assert a right to protection against exploitation and disrespectful treatment. Where restrictions of these rights might be necessary, the last article insists on legal safeguards against any kind of abuse. Five years later, these rights for intellectually disabled people were strengthened and supplemented by another UN Declaration: the 'Declaration on the Rights of Disabled Persons'.
These international efforts command worldwide respect. They were accompanied by national exertions in the same direction. In the United States and many other Western countries attempts have been made to remove social conditions that impede the application of the idea of equality to the intellectually disabled. The pioneers of this movement to end discrimination came mainly from Scandinavia. By the early 1960s the Dane Bank-Mikkelsen and the Swede Nirje had gained considerable notice in politics and special education because of their insistence on arranging the living conditions of people with mental disabilities in as normal a way as possible. In the United States, the champion of integration Wolf Wolfensberger took up this idea and discussed it in many articles. This internationally established principle of normalisation is in some way used as a normative test in special education as well as in social politics in order to assess the living conditions of mentally disabled citizens.
With the support of the United Nations Declarations, the move to bring people with mental disabilities into the community of equals gained more and more success. For more than twenty years there has been a trend towards deinstitutionalisation. The aim is to break up the large institutions for mentally disabled people. Living in the community has become part of a whole process of social integration, which is being extended to all aspects of social life. This includes school education, too. Article 2 of the Declaration on the Rights of Mentally Retarded Persons asserts a right to 'such education, training, rehabilitation and guidance as will enable [the mentally retarded person] to develop his ability and maximum potential'. This right is already being realised in several countries. In Germany, teachers for special schools are trained at universities. That means that pedagogical staff must be qualified at a high level in order to give students with mental disabilities a good education and the optimum preparation for an independent and pleasant life in their community.
Though there is no reason to be content with the present situation, the conceptual and actual progress made over the last thirty years in applying the idea of equality in favour of people with mental disabilities cannot be denied.
The Search for the Humanum
During the 1960s and 1970s more and more special schools for people with mental disabilities were founded. The students had to meet certain minimal requirements. The first official guidelines for those schools in Nordrhein-Westfalen, one of the provinces of West Germany, contain the following criteria for entrance.
(a) a mental and psychological standard of development, that allows for the recognition of objects and enables the disabled to manipulate objects in a purposeful way and spend several minutes in appropriate activities;
(b) the ability to understand simple verbal or gestural information;
(c) the ability to learn social competence.
After school education is finished, so the official guidelines noted, the students should be able to take over 'tasks in the household, kitchen and garden', to have an appropriate 'contact with animals', to use knowledge in 'health care and domestic care of the sick', to 'handle tools and machines' and possess some 'industrial skills'. Regarding this group of people, there seemed to be hardly any problems in justifying educational training. On the one hand, of course, one cannot equate the standard of schools for people with mental disabilities with standards of other state schools. But on the other hand, the educational goals involve skills and abilities, which are not of the kind to evoke serious opposition from those who have little or no contact with people with mental disabilities. The people concerned are adolescents or adults who are mentally disabled and therefore impaired in other aspects of their personality, but who will, when educated, be able to be independent in much of their everyday lives. To apply Article 1 of the UN Declaration of Human Rights in this case seems straightforward: 'All human beings are born free and equal in dignity and rights. They are endowed with reason and conscience and should act towards one another in a spirit of brotherhood.'
To found schools for people with mental disabilities and thereby give expression to our social concern for these members of society was only a first step. The conviction increased that mental disability is never a reason for withdrawing the right to an education in school. This position had consequences. If it is agreed that a mental disability cannot be a reason to deny a member of society the right to education in school, the criteria for entrance cited above can no longer be accepted. Instead it seemed obvious that the idea of equality demanded the inclusion of all students of school age regardless of their degree of mental disability. Hence the criteria of entrance cited above were dropped from the second official guidelines for schools for people with mental disabilities, drawn up in 1980. Shortly before, a ministerial prescription had ordered the admission of profoundly mentally disabled people, whose educational integration in school had not previously been planned.
In the relevant literature, those students are often described as not developing beyond the abilities of an infant of a few months old. The new official guidelines of Nordrhein-Westfalen, which were developed with the assistance of experts in the field of special education, express the view that even this low level will not be reached by every student:
Learning behaviour is characterised by impairment of the reception, preparation and storing of information and of the mode of expression. The variety of learning behaviour may range from:
- as yet, no observable interest in learning, even concerning vital needs, to an interest in learning regarding vital needs . . .
- as yet, no recognisable ability to respond to personal expressions and reactions, to the ability to respond to situations and objects . . .
— as yet, no perceptible reactions to feelings and stimuli, to a mainly action-oriented learning . . .
- as yet, no observable communication, to a reduced ability of receiving, processing and expressing verbal information.
There are a lot of other deviations, such as:
- little developed ability to co-ordinate sensorial impressions and adequate movements and behaviour . . .
— missing or reduced ability to react to persons and situations or to distance oneself from them.
Against the background of these characterisations it is worth looking again at Article 1 of the Declaration of Human Rights: 'All human beings are born free and equal in dignity and rights. They are endowed with reason and conscience and should act toward one another in a spirit of brotherhood.'
Whereas it was plausible to apply this article to the first group of people with mental disabilities entering the special schools, one must have severe doubts about its application to the second group of more severely mentally disabled students. How can we accept that a student is gifted with 'reason and conscience', when that student does not respond to any stimuli in a perceptible way, is unable to take part in communication, and cannot react to other people or his or her surroundings at all? To a certain degree these doubts can be resisted. One may reply that, first of all, the results of an intensive education as well as integrated living conditions must be seen before one judges the capacities of a profoundly mentally disabled person. The official guidelines consider this aspect by talking about 'as yet' no perceptible responses or 'as yet' no perceptible participation in communication. Secondly, even if after many years of educational efforts under optimal living conditions there is still no change, one can always point to the general progress in knowledge which leads to a continuous improvement in our educational abilities. This reply is well-founded, but it is also one-sided. It is neither logically nor empirically defensible to consider only the limitations of educational programmes and not the limitations of students.
One cannot deny that a profoundly mentally disabled young man, let us say at the age of eighteen, may never exceed the minimal capacity of an infant, despite committed educational efforts and optimum social surroundings. To deny this would mean closing our eyes before an unpleasant reality and giving our wishes the status of pedagogical premise; which defy human experiences.
But it is not necessary to look at the lowest end of human capacity in order to analyse the moral dilemma which is associated with the inclusion of profoundly mentally disabled students among the clientele of special education. The fact that these adolescents seem to be missing — perhaps for all their lives — what we commonly consider characteristic human abilities has indeed evoked a lot of confusion in the field of special education, and especially in its ethical aspects. Faced with this new situation and confronted with the extremely minimal capacities of these human beings, we are forced to look again for what should be regarded henceforth as human, as the humanum.
In the context of a research project, Pfeffer tells of the impression of one of his colleagues who makes contact with a profoundly mentally disabled student for the first time:
Everything that makes a difference between humans and animals seems to be missing: abstract thinking and language as typical human attributes could be eliminated right away. What remains, then? . . . What is a human being, this measure of everything, if the profoundly mentally handicapped are humans too?
Profoundly Mentally Disabled Humans and Nonhuman Primates: A Comparison
For the first time in special education humans were compared to animals. Such comparisons were regarded as an especially convincing strategy for upholding a special moral status for humans among all other living beings, even in cases of profound mental disability. 'In biological anthropology', the well-known Dutch educationalist Stolk tells us, 'you try to find out this typical humanum by comparing humans to animals'. Parents of severely mentally disabled children also draw such comparisons, as an example from the same source demonstrates:
The parents of Johan show the photo album with their son. The photos of successive years indicate increasingly how serious the disability of their son is. Then the photos stop. The boy is now 14 years old, but there is no photo since he was 7. Those who know Johan don't ask why. His father says of him: 'You get more love from a pet.' After a long period of silence, he adds with bitterness: 'He lives like a plant, like a poorly blooming weed.' And after another long pause: 'But the crazy thing is, he always remains your child.'
From this example Stolk draws the following conclusion:
If we compare human beings to animals, the mentally disabled seem to lack those attributes which are commonly described as typically human. In some respects profoundly mentally disabled people even fail to bear comparison with animals.
What does 'in some respect' exactly mean? Andreas Froehlich is a special educationalist who has done a lot of research in the field of advancement of severely mentally disabled people. One of his most recent articles about communication with profoundly mentally disabled people starts with an attempt to state the existential meaning of communication. He notes that in medical guidelines on the limits of medical treatment for profoundly disabled newborns it is pointed out that the ability to communicate may become the ultimate measure of human individuality. Then he writes: 'Life and ability to communicate virtually go together, and thus this communication gets more and more importance for our human self-understanding.' Together with Ursula Haupt, a psychologist, he tries to develop a system of communication in which perception, emotions, cognition, movement, body experience and social experience all interact with each other and with communication. He emphasises the interdependences and influences of the separate areas on communication. Against the background of a profound mental disability, different aspects of communication were treated separately: visual and tactile, vibratory, smell and taste. Froehlich further differentiates the physical area into body contact, proximity, orientation, gaze, eyebrows, posture, facial expression and intonation. He also describes, from the viewpoint of educational advancement, the influence of feelings, cognition, and social and physical experiences.
It is not quite clear what Froehlich means when he says that he has found a 'preliminary possibility of describing complex human development'. If this is supposed to mean that his scheme is only applicable to human beings, it clashes with what we know about, for example, nonhuman primates. Jane Goodall's book The Chimpanzees of Gombe describes the results of twenty-five years of research on chimpanzees. In the sixth chapter, on communication, Goodall begins by describing how chimpanzees communicate feelings such as fear, stress, anger, pleasure and so on. Different ways of communication are analysed, including visual communication, tactile and auditory communication, olfactory communication, and various combinations of these.
It is revealing to see that every aspect of communication discussed in Froehlich's article on communication with severely mentally disabled people is also discussed in Goodall's chapter on the communication of chimpanzees. But that is not all. There is nothing that humans with the most serious intellectual disabilities can do or feel that chimpanzees or gorillas cannot; moreover, there is much that a chimpanzee or a gorilla can do that a profoundly mentally disabled human cannot do. This includes the characteristics generally regarded as distinctive of human beings. To show this, here are some examples relevant to language, intelligence and emotional life.
Like other educationalists in this field Froehlich points out that profoundly mentally disabled people have as little real linguistic competence as very young children. Compare this with Francine Patterson's descriptions of the abilities of two gorillas, Koko and Michael, in Chapter 6 of this book and elsewhere. Both Koko and Michael take the initiative in beginning conversations with humans. They use their vocabulary in creative and original combinations to describe their surroundings, their feelings, their wishes and their personal experiences. They understand spoken English and have been taught to read some written language. Patterson adds that dialogues with gorillas are like dialogues with small children and therefore in many cases special interpretations and completions are necessary. Jane Goodall's research mentioned above reports on many successful experiments teaching chimpanzees and other nonhuman primates to use symbolic means of communication. Allen and Beatrice Gardner taught Washoe to use American Sign Language, as described by Roger and Deborah Fouts in Chapter 4. At the age of 5 years, she understood 350 different symbols and she was able to use about 150 of them in an active way. She transfers signs from one context to another in a correct manner. Thus she learned the meaning of 'open' in connection with doors and used it correctly to refer to opening the refrigerator or other containers. The scientists Duane M. Rumbaugh and Timothy V. Gill found during their lessons with the chimpanzee Lana that she correctly uses stock sentences in various contexts. Like Francine Patterson they observed that Lana initiated conversations and invented new variations and combinations of known words. Lana even created new names for certain objects by freely combining learned signs.
Even without further examples and deep analysis it can be said that these apes show a linguistic competence that cannot be achieved by profoundly mentally disabled humans even after long and intensive training. At the end of their study with Lana, Rumbaugh and Gill also
mentioned the fundamental dependence of linguistic skills on intelligence: 'We believe that the success Lana has had so far in acquiring linguistic-type skills supports our view of language — that the foundations of language are to be found in the processes of intelligence.' What do we know about the higher cognitive abilities of chimpanzees and other nonhuman primates as revealed, not only in the use of language but also in solving other problems?
Research on the mental capacities of chimpanzees and gorillas reaches further back than investigations on severe mental disability in human beings, which has only recently become a topic of educational and psychological research. Most of the currently used intelligence tests are not suitable for profoundly mentally disabled people, because the tests demand a level that is simply too high for these people. But Patterson reports using the Stanford-Binet Children's Intelligence Test with Koko (her results were in the below-average human range). Patterson also refers to other tests she carried out with Koko, including tests of intelligence, of development and of language, such as the Cattel Infant Intelligence Scale, the Bayley Scales of Infant Development, the McCarthy Scales of Children's Abilities, etc. From the results she concludes that there may be much more happening in the minds of gorillas than we commonly suppose today. An experiment by Doehl, cited by Goodall, demonstrates the ability of Julia, a six-year-old chimpanzee, to calculate, in a deliberate manner, how to reach, by means of five separate steps, a box with a banana in it. In the experiment two series of five closed and transparent containers were put before Julia. One of the goal boxes was empty, the other contained a banana. To open the box containing the banana, Julia had to get a distinctively shaped key from another box. But this box was closed too and could only be opened with its own distinctive key. This key Julia had to take out from a third box, also locked and also requiring its own key. . . and so on. Working backwards from her desire to obtain the key for the last box with the banana, Julia was able to choose the right one of the initial two keys, lying in the first two open boxes.
Many other observations by Goodall and her colleagues demonstrate that the mental capacities of nonhuman great apes are far above the level of profoundly mentally disabled humans. This is quite evident when we remember the cognitive abilities referred to in the guidelines mentioned in the previous section and compare them to the abilities of Julia, Lana, Koko, Michael or Washoe.
The scheme for communication devised by Andreas Froehlich and Ursula Haupt takes another important aspect into consideration: the realm of feelings or emotions. Emotions cannot be observed directly. Sometimes in special education they are treated as if they represent a substantial difference between humans and animals. However, as early as 1872, in his Expression of the Emotions in Man and Animals, Charles Darwin had shown by detailed observations that the expression of emotions in nonhuman primates is closely analogous to that in human beings. Often he describes in a subtle way how feelings of joy, pleasure, excitement, and also of pain, anger, disappointment and fright are expressed. The systematic observations of modern researchers such as Goodall refute any claims that there is something unique about humans with regard to their expression of feelings and emotions. These observations provide convincing evidence of a rich emotional life in nonhuman great apes. For example, fifteen different calls of the chimpanzees were recorded by sound-spectrograph-analysis. From this basis Goodall and her colleagues identified further variations over more than 50,000 hours of observation. By a controlled rating system they found a definite congruence in more than thirty discrete calls, expressing feelings of fear, confusion, sexual excitement, pleasure, social apprehension and so on. They report similar findings about the emotional meaning of different facial expressions, postures and movements for communication and interaction.
Perhaps these results are still not sufficiently well established. But there is no doubt that they give more definite grounds for accepting that chimpanzees have a rich emotional life than any comparable information about profoundly intellectually disabled people does for our belief in the richness of their emotional life. Statements and presumptions about the inner perspective of the profoundly intellectually disabled, and about their feelings and moods, are presently supported only by the subjective impressions of persons trying to build contacts with them. They often live lost in their own autistic world so that over a longer term, little can be found out about their inner lives, and we must resort to speculation. So, for example, in the context of a research project Pfeffer cited the following observations from his colleagues concerning a profoundly disabled student:
[She] had a really pretty face. . . . But in this sympathetic face there were hardly any changes that might give any indication of an interest in what happened around her. It was as if the girl was in a glass case in a corner of the classroom, cut off from her environment and alone with her body and herself. She showed no reaction to touch or noise, she seemed to see nobody and nothing.
Later on another colleague reported:
Pia was strange and inaccessible to me. I did not understand her and she did not make herself understood by me. The usual means of contacting strangers, the competence of verbal communication, were totally missing.
Even when it is realised that special training over a long period often leads to recognisable progress, the limits of education are not to be denied. Pointing to another student in his project, Pfeffer says:
Like all the other profoundly mentally disabled people Wolfi, too, has great difficulties in communicating . . . The human environment is especially unavailing for children with strong autistic traits to whom we can apparently make no contact.
Towards a Consistent Idea of Equality
Our considerations started with the statement that people with a mental disability have come late to the rights laid down in the Declaration of Human Rights of 1948. If they have completed training in special schools, many people with mental disabilities today will be able to lead an independent life in many respects. But in general, a protective environment and social services are necessary to enable them to live a satisfying life in their community. We then noted that special education encountered difficulties when at the end of the 1970s profoundly mentally disabled children were admitted into schools. The difficulties were not just in finding the best means of advancing the development of these children, but also over the moral justification of the rights to education claimed for them. Distinctively human qualities, easily recognisable in mildly and moderately mentally disabled people, could no longer provide a decisive moral basis for this right, because among profoundly mentally disabled people, such qualities are at best found only in a rudimentary form.
In the normative discipline of special education this situation led directly to the comparison of humans and animals in order to conserve the superior moral status of humans among all feeling beings on the planet. Here appeared two incompatible facts: on the one hand it had to be recognised that the distinctive human qualities are virtually absent from people with profound mental disabilities. On the other hand there was a growth in our knowledge of the existence of so-called typical human characteristics, such as language, intelligence and emotions, in a high degree in other nonhuman living beings. As the previously mentioned research shows, these findings do not rest on any sentimental basis, but on a solid grounding of fact. Knowledge of the varied social life of nonhuman primates has recently become available to the German-speaking public in a number of popular scientific books.
Nevertheless, in special education the conviction that still predominates is one based on an idea of equality which proceeds from an image of a human being gifted with reason and conscience. Where it is recognised that those typical human qualities are really neither typically human nor present in all human beings, the idea of equality suffers a metamorphosis which contradicts its fundamental sense. Faced with this situation Stolk suggests 'that in giving an answer to the question of humanness we should not start from the differences between human beings but from what is common to them, regardless of their abilities and qualities'. He cites a proposal intended to reveal this humanness, this new humanum: 'Human is every being born from a human being.'
Anyone who interprets the idea of equality so as to find the criterion of equality only in membership of the species Homo sapiens can include profoundly mentally disabled people in the community of equals. It is done as Stolk describes, 'regardless of their abilities and qualities'. This interpretation is as psychologically strong as it is morally weak. For it prefers all and only members of that group who created this interpretation, discriminating without valid reason against all other living beings who are not members of this privileged community of equals.
The attempt to realise the idea of equality is made more difficult when those who are not members of the relevant moral community are unable to appeal against their exclusion. Not even the most intelligent chimpanzees can protest, either directly or through representatives drawn from their own kind, against the deprivation of liberty, against being used in painful medical experiments, against being killed for food, or against being exhibited in zoos and circuses. On the other hand, according to the Declaration of the United Nations, the profoundly mentally disabled human is protected from any kind of abuse and degradation, merely on the grounds of membership of the species Homo sapiens. Should the deeper sense of the idea of equality, on which human rights is based, demand that we provide for the interests and needs of humans but allow discrimination against the interests and needs of nonhuman beings? Wouldn't it be strange if the same idea contains the claim for equality and the permission for discrimination, too? Can this idea really involve sympathy and cruelty at the same time?
In this situation special education is at a moral crossroads. It could stay on its traditional path, content that the progress of the idea of equality finally has reached all its clientele. Now that it is well known, particularly in this discipline, that those typically human qualities can no longer provide a relevant moral foundation for the way in which we treat all human beings, the point of view could be taken, without any consideration of other consequences, that membership of the human species is enough. Perhaps this would happen without any deliberate desire, on the part of members of the discipline, to support the traditional view that in future (for example) painful medical experiments might be performed on beings like Julia but not on those like Pia, simply because Julia is a chimpanzee and Pia is a human being.
The discipline of special education for severely mentally disabled people could choose another way which makes possible a more thorough-going pursuit of the idea of equals. We have to realise that this discipline deals with research and the advancement of minimum needs which require respect even under circumstances in which typically human abilities are no longer found. It is precisely this discipline that has enough moral standing to point out that the fundamental sense of the idea of equality demands principled and equal respect for every need and every interest, no matter whether it is a need of a Julia or of a Pia. Of course it is not the task of special education to care about the destiny of those miserable apes, defencelessly vegetating in laboratories, often until they meet their brutal death. But the discipline offends against its own principles if its ethical disputes about justifying the educational requirements of profoundly mentally disabled humans are settled by the arbitrary exclusion of living beings who are sentient and defenceless, too, and whose only 'fault' is not to be a member of the species Homo sapiens.
The knowledge we have today about profoundly mentally disabled humans and nonhuman primates gives strong reason to revise the traditional interpretation of the idea of equality. The time has come to see the community of equals no longer as a closed society, but as an open one. The admission of nonhuman primates and the guarantee of certain fundamental rights in favour of all members of such a community, including profoundly mentally disabled humans, would be a first important step. These rights should include the right to life, the protection of individual liberty and the prohibition of torture.
 Universal Declaration of Human Rights (Official Records of the third session of the General Assembly, Part 1,10 December 1948. United Nations, Palais de Chaillot, Paris, 1949), p. 72.
 H.T. Mill, 'Enfranchisement of women', in J. S. Mill and H. T. Mill, The Subjection of Women: Enfranchisement of Women (Virago, London, 1983), S. 9.
 Declaration on the Rights of Mentally Retarded Persons (Resolution adopted by the General Assembly during its twenty-sixth session, 20 December 1971. General Assembly Official Records Suppl. No. 29 (A/8429). United Nations, New York, 1972), p. 93.
 Declaration on the Rights of Disabled Persons (Resolution adopted by the General Assembly during its thirtieth session, 9 December 1975. General Assembly Official Records Suppl. No. 34 (A/10034). United Nations, New York, 1976).
 RichtlinienfurdieSchulefiirGeistigbehinderte(Sonderschule)inNordrhein-Westfalen (Schwann, Diisseldorf, 1973), p. 6.
 Ibid., p. 12.
 Aufnahme Schwerstbehinderter in Sonderschulen (Kulturminister des Landes Nordrhein-Westfalen v. 12.7.1978 - II A5.365/0 - 1831/78).
 Richtlinien und Hinweise fur den Unterricht. Forderung schwerst-behinderter Schiiler (Greven, Koln, 1985), pp. 6ff.
 J. M. Kauffman and J. Krouse, 'The cult of educability: searching for the substance of things hoped for; the evidence of things not seen', Analysis and Intervention in Developmental Disabilities, vol. 1 (1981), pp. 53-60.
 W. Pfeffer, Forderung schwer geistig Behinderter. Eine Grundlegung (Edition Bentheim, Wiirzburg, 1988), p. 128.
 J. Stolk, 'Geistig behindert mil dem Verlangen, auch jemand zu sein' in J. Stolk and M.J.A. Egberts (eds), Uber die Wtirde geistig behinderter Men-schen (Lebenshilfe Selbstverlag, Marburg, 1987), pp. 5—34.
 Ibid., p. 8.
 Ibid., p. 10.
 A. D. Froehlich, 'Ganzheitliche Kommunikationsforderung fur schwerer geistig behinderte Menschen', in A.D. Froehlich (ed.), Lernmoglichkeiten, 2nd edn (HVA Schindele, Heidelberg, 1989), pp. 17-44.
 Ibid., p. 17.
 Ibid., p. 19.
 J. Goodall, The Chimpanzees ofGombe. Patterns of Behavior (The Belknap Press of Harvard University Press, Cambridge, MA, 1986).
 F. Patterson, 'The mind of the gorilla: conversation and conservation', in K. Benirschke (ed.), Primates, the Road to Self-sustaining Populations (Springer, New York, Berlin, Heidelberg, 1986), pp. 933-47.
 D. M. Rumbaugh and T. V. Gill, 'Lana's acquisition of language skills', in D. M. Rumbaugh (ed.), Language Learning by a Chimpanzee. The Lana Project (Academic Press, New York, San Francisco, London, 1977), S. 191, pp. 165-92.
 J. Dohl, 'Uber die Fahigkeiten einer Schimpansin, Umwege mit selbstandigen Zwischenzielen zu iiberblicken', Zeitschrift fur Tierpsychologie, vol. 25 (1968) pp. 89-103.
 Pfeffer, Foerderung schwer geistig Behinderter, p. 111.
 Ibid., p. 115.
 Ibid., p. 126.
 D. Fossey, Gorillas im Nebel. Mein Leben mil den sanften Riesen (Kindler Miinchen, 1989); J. Goodall, Wilde Schimpansen. Verhaltensforschung am Gombe Strom (Rowohlt, Reinbek b., Hamburg, 1991); F. de Waal, Wilde Diplomaten. Versoehnung und Entspannungspolitik bet Affen und Men-schen (Hanser, Miinchen, Wien, 1991).
 Stolk, 'Geistig behindert mit dem Verlangen' p 14.
 Ibid., p. 15.