My work cited

On this page I describe how my work with the signing apes has been cited and quoted in publications by others.

My work discussed in a fascinating book on the origins of human language

In 2008 MIT Press published Michael Tomasello’s book Origins of Human Communication, which was based on lectures that Tomasello gave in Paris in 2006. The book is a fascinating account of how human language may have evolved out of ape gestures. Based on the latest scientific knowledge on the use of gestures by apes and language development in human children, Tomasello makes a quite plausible and elegant argument that human language has had its origins in great ape gestural communication. This is because ape vocalizations are not learned. The vocalizations are used inflexibly, tied to the emotions that give rise to them. Great ape gestures, however, show much more flexibility and the use of gestures is learned during development. Great apes also use their gestures intentionally, they wait for a response from their conspecifics and will repeat or adjust the gestures if there has been no response. Though Tomasello has of course no clear-cut story of how exactly human language may have evolved, the argument for a gestural origin is solid, given these differences between great ape vocalizations and gestures. Tomasello divides great ape gestures into attention-getters and intention-movements. A gesture such as a mother asking her child to climb on her back, is an example of an intention movement: the movement of the gesture shows the intention that the mother wants to take place. The use of gestures by great apes is, however, limited to making requests to and demanding actions from others. In contrast, human communication includes motives for helping and sharing, which results in three basic motives of human communication: requesting (requesting help), informing (offering information) and sharing emotions and attitudes (bonding). These motives have come about because unlike nonhuman great apes, who have a comprehension of individual intentionality only (they know what the goals are of separate individuals), humans have skills for what is called shared intentionality: human individuals have a common conceptual ground, they have shared goals and attention and communicate with cooperative motives. These skills and motives arose in a context of mutualistic collaborative activities. Originally starting with pointing and using iconic gestures (pantomiming), humans experienced a “drift to the arbitrary,” eventually resulting in the linguistic conventions that we now know. Even grammar thus originated in human cooperative communication, because the human motives for informing and sharing needed the possibility to communicate about events displaced in time and space and to share further information about events and people that can only be expressed by certain aspects of grammar. mark the particular roles of participants and to relate events to one another as in stories and narratives. Grammatical constructions would have come about by a conventionalization process and there would thus be no need to infer a universal grammar such as Chomsky proposed: grammar is learned, not innate. The fact that grammar is part of every human language is because it is functional and necessary for our particularly human way of cooperative communication, not because grammatical rules are hard-wired in our brains.

I know this is a very short summary of Tomasello’s argument for the gestural origin of human language, so I advise you to read the book in order to understand his full argument. The book is written in a very clear and convincing style and is understandable for most lay persons with some academic background.

Chapter 6 is about the possible evolution of grammar and it is here that Tomasello gives ample space to discussing my work with the signing chimpanzees. He mentions that there has been a controversy about the lack of grammatical structure in the use of signs or lexigrams by the great apes in the language projects, because of a lack of systematic and quantitative data. My work with Washoe and the other signing chimpanzees has been exactly that: a large systematic analysis of the way the chimpanzees use their signs. My study is then presented by Tomasello on a par with the study of Sue Savage-Rumbaugh and Patricia Greenfield (published in 1990) of the way the bonobo Kanzi used his lexigrams.Both studies are the only ones in ape language research that systematically analyzed the videotaped behaviour of these ape subjects. Tomasello discusses the results of my study in several pages, presenting my conclusions on the communicative intentions or functions of the apes’ signed utterances and the lack of grammatical structure in the sequences of signs that the chimpanzees produced. He presents the only ordering that I found in the apes’ sign combinations: the chimps used object and action signs first, and a point (to the requested object or to the human) and signs that functioned as wild cards (pleasing the human) last. He quotes my 2005 conclusion in the Journal of Comparative Psychology:

“The object and action signs are produced first because these are the more important or salient signs of the (usually request) utterances, specifying what is requested. The request markers THAT/THERE/YOU/GOOD/HURRY are produced last because they are less important (not specifying what is requested) and function to add emphasis or to spur the human into action.” I feel great my work is being discussed in this great book and I’m grateful my hard work is now of use in theories and conclusions about ape communication and the evolution of human language.”

Michael Tomasello (1950) is a psychologist who originally worked at Emory University, Atlanta (where he did a lot of research on the apes at the Yerkes National Primate Research Center). Since 1998 he is professor at theDepartment of Developmental and Comparative Psychology of the Max Planck Institute for Evolutionary Anthropology (of which he is co-director) at Leipzig University, Germany. His research staff continues to do important studies on all four great ape species’ communicative behaviour and social cognition. The Koninklijke Nederlandse Akademie van Wetenschappen (Royal Dutch Academy of Sciences) has rewarded him the2010 Dr. A.H. Heineken Prize for Cognitive Science.


Cited in an article that advocates neuroscientific research with great apes.

Todd M. Preuss. (2006). Who’s afraid of Homo sapiens? Journal of Biomedical Discovery and Collaboration, 1, 17. Click here for the article itself.

Dr. Todd Preuss is associate research professor at the Division of Neuroscience of Emory University’s Yerkes National Primate Research Center in Atlanta. He carries out fundamental research on the structure and evolution of the primate cerebral cortex. He compares the anatomy of cortical layers and areas in humans, chimpanzees and monkeys. In this article Preuss discusses the recent attempts to stop doing experiments with great apes. He argues that chimpanzees and other great apes should still be available for (non-invasive) research, in order to obtain a better understanding of the species-specific features of the human brain. My article in the Journal of Comparative Psychology gets cited when he talks about how comparative research with humans and apes has changed through the years: “Popular culture today takes it as given that apes share with humans the capacity for language. Students of language, however, have for the most part drawn the opposite lesson from the ape-language project, concluding that apes demonstrate little productive language capacity, even after intensive training, and that language is a human specialization (e.g., [5-12]).” The references cited here include my article, together with work by Steven Pinker, Seidenberg and Petitto, Terry Deacon, Philip Lieberman, Michael Tomasello, and Joel Wallman’s 1992 book Aping language.

It is true that my research with the signing chimpanzees has shown that the apes’ signing behaviour cannot be considered linguistic and I claim that language is species-specific for humans only. However, and this is what I feared when I obtained my results, my conclusion about the absence of language in nonhuman apes should not lead to the idea that it is therefore morally justified to treat nonhuman apes different from humans, simply because of this difference. In the Epilogue of my dissertation I discuss the moral implications of my findings. Instead of interpreting my data as a justification for using great apes in research, I argue that we should still treat all sentient animals equally. This is because only sentience or phenomenal consciousness is the necessary condition for inherent value and therefore for equal treatment, and not a more complex cognitive capacity such as language (see also my 1997 chapter in Animal consciousness and animal ethics). I have to admit that Preuss does not use my work here to advocate a moral difference in treatment between humans and nonhumans, and only refers to it to show the changes in thought of comparative researchers. However, it is interesting that my work is cited in an article that argues for the continuing use of great apes in biomedical research.

Preuss makes claims in the article that are morally objectionable. He says that we need more comparative studies of the brain, for example by using neuroimagining techniques. Claiming that this is an ethically acceptable way of studying the brain in humans, he says that we could use those new techniques in nonhuman apes as well. Though I’m unfamiliar with these techniques, such research with apes will always include keeping the apes in captivity, and probably restraining them in some form or other. This is not “ethically acceptable”, because it robs the ape subjects of their individual freedom.

Another technique Preuss suggests is to do histological studies using brain tissue obtained postmortem. Again, moral questions can be posed here. With humans, we have the possibility of informed consent: the humans whose brains will be analyzed will have given consent before their death to use their brains for research. Furthermore, where will the ape brains come from? I have yet to see a chimpanzee carrying a donor card that specifies that his or her body can be used for science after death. I presume that Preuss is suggesting we carry out such brain research with apes that have died in biomedical labs or zoos. Which confronts us then again with the captivity issue. If keeping apes in captivity is morally objectionable, then so is using their brains after death.

Comparative genomics is another form of research that Preuss would like to see done, and this could be done by “employ[ing] any of the growing array of non-invasive, non-terminal techniques (biochemical, proteomic, imaging, behavioral) we have for comparing humans to other animals.” Again, the non-invasiveness and non-terminalness of such techniques leaves aside the moral problem of captivity.

Ending his article with the section Will there be chimpanzees to study? Preuss would like to see the moratorium on breeding captive chimpanzees lifted (imposed in the USA by the National Institutes of Health in 1997), so that science can continue the comparative studies that would be of great value in understanding the human brain. Especially with chimpanzees facing extinction, breeding for science should be allowed. From an egalitarian point of view, Preuss’s position here means that chimpanzees will be subject to further captivity, forced breeding and the intrusion of their freedom in comparative research. Rejecting such research because of these moral reasons means that we cannot improve our knowledge of the human brain in that way. However, with humans as scientific subjects we accept certain moral constraints, which also means that we can’t increase our knowledge in the same way as when we would allow ethically unacceptable scientific practices with humans (and I know of no scientists that advocate such practices because it would further our knowledge). Considering nonhuman animals as our moral equals means we similarly accept certain limits on the increase of our knowledge and our possibilities of fighting diseases.


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