Category Archives: Publications

New blog on veganism

A few weeks ago I have made a new blog, especially dedicated to veganism. I have been a vegan since I was 17. At that time I was already a vegetarian and feared I could never be vegan, because I enjoyed milk a lot. I then tried vegan substitutes for cows’ milk and found out that food could be just as good without any animal produce. Though being vegan can be good for your health, I am vegan because of moral reasons. I consider it most plausible that all nonhuman animals have some form of consciousness or sentience (“phenomenal consciousness” in the terminology of the British philosopher Ned Block), in the sense that they are able to experience states such as pleasure and pain. I then depart from a deontological egalitarian ethics, arguing that we should treat all animals with consciousness or sentience equally. Given the fact that humans can live perfectly healthy without animal produce, I believe that there are no sound arguments for consuming animals for their meat or dairy. For more information about my opinions on animal consciousness and animal ethics, I refer to my articles on my profile at

The new blog is called Esteban’s Vegan Side and will contain a discussion of the moral arguments for veganism. Most of all, though, I will publish tasty and delicious vegan recipes. There is still a lot of prejudice out there, considering vegan cooking to be bland and tasteless. I want to show instead that vegan cooking can be surprisingly tasty and good to the palate. I have cooked vegan food for many people who were not vegan, and they always comment how wonderfully surprised they are when they eat my vegan meals. The posts on this blog will be both in English and in Dutch.

I have already posted three recipes on my vegan blog. One for a Moroccan risotto, one for a Spanish gazpacho soup drink, and one for an Indian eggplant curry (Baingan Bartha). I have many more recipes to post. If you’re curious, take a look at my blog!


Filed under Animal Consciousness, Animal Ethics, Publications, Veganism/Vegetarianism

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 the Department 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 the 2010 Dr. A.H. Heineken Prize for Cognitive Science.

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My work cited in an article that advocates neuroscientific research with great apes

I am busy making a separate page on my blog to discuss how my work with the signing apes has been cited and quoted in publications by others. The first article of that page I discuss here in this post. It’s: 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 Dereck Bickerton, Steven Pinker, Marc Seidenberg and Laura 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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My articles on Animal Consciousness now online

Yesterday I scanned all my publications about animal consciousness and uploaded them to my profile on In the 1990s I published several articles on the subject together with my brother Titus Rivas. In these articles we advocate the analogy postulate as the way to assume subjective, phenomenal consciousness or sentience in at least all vertebrate animals. The analogy postulate looks at similarities between humans and other animals in behaviour and nervous system and from these similarities infers the existence of phenomenal consciousness, just as we do when we postulate sentience in other humans. The articles now online on and downloadable there include the 1991 Bewustzijn bij dieren [Consciousness  in animals] published in Antropologische Verkenningen and the 1992 The use of analogous reasoning for assessing discomfort in laboratory animals, published in Animal Welfare. I also uploaded a 2007 interview with me by Dr. Pouwel Slurink about my work with the signing apes in Filosofie. I wish you all lots of reading fun and again, let me know what you think about the articles!


Filed under Animal Consciousness, General, Publications

My chapter on Animal Ethics now online

In 1997 I edited a book about animal consciousness and animal ethics, together with my co-editors Marcel Dol, Kasanmoentalib, Susanne Lijmbach and Ruud van den Bos. We gave it the title Animal consciousness and animal ethics. Perspectives from the Netherlands, published by Van Gorcum in Assen, The Netherlands. In the book scientists and philosophers from The Netherlands wrote a chapter about the issues of animal consciousness and animal ethics. My own contribution was called Psychological complexity and animal ethics: Choosing between hierarchy and equality and discussed the positions in animal ethics of the famous philosophers Peter Singer, Tom Regan and Donald VanDeVeer. I ended up criticizing all of them actually, in that I argue for a view where only phenomal consciousness or sentience is the necessary condition for inherent value and therefore an egalitarianism for all sentient animals is called for. Equal treatment of all sentient animals in practical terms means we stop using nonhuman animals for food or for entertainment purposes such as circuses, stop experimenting on them and stop taking away their liberty such as in zoos.

Today I scanned the chapter from the book and uploaded it to my profile on, a great network site of academicians. You can read and download almost all my publications there. My dissertation, my articles in academic journals and several powerpoint presentations of lectures that I gave about my work with the signing chimpanzees. Click here to go directly to my chapter on animal ethics. Have fun reading and let me know what you think!

Addition from May 28, 2010: The whole book Animal Consciousness and Animal Ethics is now available as a Google Book. You can read it here, but not download it.

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Dissertation now published at Radboud University

Today my dissertation was included in the Radboud Repository, the electronic deposit of academic publications of the university library of Radboud University (Nijmegen University). This is the link to it, which you should also use when you want to refer to or cite and quote my dissertation of 2003:

When you click on the link you will come to this page:

Anyone interested in my work on signing chimpanzees can download the dissertation there directly, there is no subscription or anything needed.

To include my work in a reference list, the APA style reference would be like this:

Rivas, E. (2003). GIMME GIMME GIMME. The recent signing behaviour of         chimpanzees (Pan troglodytes) in interactions with longtime human companions. Retrieved from

Having been included in the Radboud Repository, my dissertation is now also included in PiCarta, the portal to the Dutch Union Catalogue and other databases.

I feel great and proud about all this! Finally my work is published and open for anyone to read. Years of hard work have reached fruition at last.

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Electronic version of my dissertation!

Today I’ve finished working on the electronic version of my dissertation GIMME GIMME GIMME. The recent signing behaviour of chimpanzees (Pan troglodytes) in interaction with longtime human companions, for which I got my doctoral degree in April 2003 from the University of Nijmegen (now called Radboud University). The dissertation has a complete overview of all the research that has been carried out with signing chimpanzees, including the famous Washoe, the first ape who was taught signs with which to communicate with humans. It also has the full details of my study of the signing chimpanzees at the Chimpanzee and Human Communication Institute (CHCI) of Central Washington University on their recent use of signs during the 1990s when they were in interaction with humans they had known for a long time.

The first chapter of GIMME GIMME GIMME discusses the history of the projects with signing chimpanzees. The second chapter then presents the various results of the projects with regards to signs, combinations of signs, discourse and conversational skills, the communicative intentions of the sign use, and the question whether the signing of chimpanzees should be interpreted as language or not. In the third chapter I discuss the problems of setup, method and interpretation of which sign language research with chimpanzees has suffered. In chapter 4 my study of the recent sign use of the famous signing chimpanzees is fully presented, with lots of tables and data. And with a surprising conclusion, given that I found that the signing behaviour of these chimpanzees could not be considered linguistic at all. Chapter 5 then includes the discussion of my findings, the question whether the chimpanzee signs can be interpreted as symbols or contioned responses, and the chimpanzee sign use is compared with the use of lexigrams by the famous bonobo Kanzi.

When I got my doctoral degree in 2003 I was unable to publish my dissertation because of the contractual constraints I had with the CHCI. When I was finally able to publish I contacted several scientific publishers to suggest a book based on my dissertation. For various reasons these publishers declined to publish it and meanwhile time moved on. So now I decided to wait no longer to get my work and these important results out into the open and for all to read. Click here to download my dissertation!

The dissertation is now in pdf format which means I can send it to the University of Nijmegen to have it posted with their electronic publications. This is an open site with access for everyone. Meanwhile I’m planning to write a popular-scientific book about my whole story with the signing apes. Stay tuned for more to come!

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