Animal Consciousness

First published Sat Dec 23, 1995; substantive revision Wed Oct 13, 2010

There are many reasons for philosophical interest in nonhuman animal (hereafter “animal”) consciousness. First, if philosophy often begins with questions about the place of humans in nature, one way humans have attempted to locate themselves is by comparison and contrast with those things in nature most similar to themselves, i.e., other animals. Second, the problem of determining whether animals are conscious stretches the limits of knowledge and scientific methodology (beyond breaking point, according to some). Third, the question of whether animals are conscious beings or “mere automata”, as Cartesians would have it, is of considerable moral significance given the dependence of modern societies on mass farming and the use of animals for biomedical research. Fourth, while theories of consciousness are frequently developed without special regard to questions about animal consciousness, the plausibility of such theories has sometimes been assessed against the results of their application to animal consciousness.

Questions about animal consciousness are just one corner of a more general set of questions about animal cognition and mind. The so-called “cognitive revolution” that took place during the latter half of the 20th century has led to many innovative experiments by comparative psychologists and ethologists probing the cognitive capacities of animals. The philosophical issues surrounding the interpretation of experiments to investigate perception, learning, categorization, memory, spatial cognition, numerosity, communication, language, social cognition, theory of mind, causal reasoning, and metacognition in animals are discussed in the entry on animal cognition. Despite all this work, the topic of consciousness per se in animals has remained controversial, even taboo, among scientists, even while it remains a matter of common sense to most people that many other animals do have conscious experiences.

  • 1. Concepts of Consciousness
  • 2. Historical Background
  • 3. Basic Philosophical Questions: Epistemological and Ontological
  • 4. Applying Philosophical Theories
  • 4.1 Varieties of dualism
  • 4.2 Physicalist accounts
  • 4.3 Neurofunctional accounts
  • 4.4 Representationalist accounts
  • 4.5 Higher-order theories
  • 4.6 Limits of philosophical theories
  • 5. Arguments Against Animal Consciousness
  • 5.1 Dissimilarity arguments
  • 5.2 Similarity arguments
  • 5.3 Arguments from the absence of self-consciousness
  • 5.4 Methodological arguments
  • 6. Arguments For Animal Consciousness
  • 6.1 Similarity arguments
  • 6.2 Inference to the best explanation
  • 6.3 Interpretivism
  • 7. Current Scientific Investigations
  • 7.1 Animal pain and suffering
  • 7.2 Animal emotions
  • 7.3 Perceptual phenomenology
  • 7.4 Self-consciousness and metacognition
  • 7.5 Evolution of consciousness
  • 8. Summary
  • Bibliography
  • Other Internet Resources
  • Related Entries

1. Concepts of Consciousness

In discussions of animal consciousness there is no clearly agreed upon sense in which the term “consciousness” is used. Having origins in folk psychology, “consciousness” has a multitude of uses that may not be resolvable into a single, coherent concept (Wilkes 1984). Nevertheless, several useful distinctions among different notions of consciousness have been made, and with the help of these distinctions it is possible to gain some clarity on the important questions that remain about animal consciousness.

Two ordinary senses of consciousness which are not in dispute when applied to animals are the sense of consciousness involved when a creature is awake rather than asleep[1], or in a coma, and the sense of consciousness implicated in the basic ability of organisms to perceive and thereby respond to selected features of their environments, thus making them conscious or aware of those features. Consciousness in both these senses is identifiable in organisms belonging to a wide variety of taxonomic groups (see, e.g., Mather 2008).

A third, more technical notion of consciousness, access consciousness, has been introduced by Block (1995) to capture the sense in which mental representations may be poised for use in rational control of action or speech. This “dispositional” account of access consciousness — the idea that the representational content is available for other systems to use — is amended by Block (2005) to include an occurrent aspect in which the content is “broadcast” in a “global workspace” (Baars 1997) which is then available for higher cognitive processing tasks such as categorization, reasoning, planning, and voluntary direction of attention. Block believes that many animals possess access consciousness (speech is not a requirement). Indeed, some of the neurological evidence cited by Block (2005) in support of the global workspace is derived from monkeys. But clearly an author such as Descartes, who, we will see, denied speech, language, and rationality to animals, would also deny access consciousness to them. Those who follow Davidson (1975) in denying intentional states to animals would likely concur.

There are two remaining senses of consciousness that cause controversy when applied to animals: phenomenal consciousness and self-consciousness.

Phenomenal consciousness refers to the qualitative, subjective, experiential, or phenomenological aspects of conscious experience, sometimes identified with qualia. (In this article I also use the term “sentience” to refer to phenomenal consciousness.) To contemplate animal consciousness in this sense is to consider the possibility that, in Nagel's (1974) phrase, there might be “something it is like” to be a member of another species. Nagel disputes our capacity to know, imagine, or describe in scientific (objective) terms what it is like to be a bat, but he assumes that there is something it is like. There are those, however, who would challenge this assumption directly. Others would less directly challenge the possibility of scientifically investigating its truth. Nevertheless, there is broad commonsense agreement that phenomenal consciousness is more likely in mammals and birds than it is in invertebrates, such as insects, crustaceans or molluscs (with the possible exception of some cephalopods), while reptiles, amphibians, and fish constitute an enormous grey area for most scientists and philosophers. However, some researchers are even willing to attribute a minimal form of experiential consciousness to organisms that are phylogenetically very remote from humans and that have just a few neurons (Ginsburg & Jablonka 2007a).

Self-consciousness refers to an organism's capacity for second-order representation of the organism's own mental states. Because of its second-order character (“thought about thought”) the capacity for self consciousness is closely related to questions about “theory of mind” in nonhuman animals — whether any animals are capable of attributing mental states to others. Questions about self-consciousness and theory of mind in animals are a matter of active scientific controversy, with the most attention focused on chimpanzees and to a more limited extent on the other great apes. As attested by this controversy (and unlike questions about animal sentience) questions about self-consciousness in animals are commonly regarded as tractable by empirical means.

The remainder of this article deals primarily with the attribution of consciousness in its phenomenal sense to animals, although there will be some discussion of access consciousness, self-consciousness and theory of mind in animals, especially where these have been related theoretically to phenomenal consciousness — as, for instance, in Carruthers' (1998a,b, 2000) argument that theory of mind is required for phenomenal consciousness. (For more discussion of self awareness and metacognition see the section on theory of mind and metacognition in the Encyclopedia's entry on Animal Cognition.)

2. Historical Background

Questions about animal consciousness in the Western tradition have their roots in ancient discussions about the nature of human beings, as filtered through the “modern” philosophy of Descartes. It would be anachronistic to read modern ideas about consciousness back into the ancient literature. Nevertheless, because consciousness is sometimes thought to be a uniquely human mental phenomenon, it is important to understand the origins of the idea that humans are qualitatively (and “qualia-tatively”) different from animals.

Aristotle asserted that only humans had rational souls, while the locomotive souls shared by all animals, human and nonhuman, endowed animals with instincts suited to their successful reproduction and survival. Sorabji (1993) argues that the denial of reason to animals created a crisis for Greek thought, requiring a “wholesale reanalysis” (p. 7) of the nature of mental capacities, and a revision in thinking about “man and his place in nature above the animals” (ibid.). The argument about what is reasoning, and whether animals display it, remains with us 25 centuries later, as evidenced by the volume Rational Animals? (Hurley & Nudds 2006). The Great Chain of Being derived from early Christian interpretation of Aristotle's scale of nature (Lovejoy 1936) provides another Aristotelian influence on the debate about animal minds.

Two millennia after Aristotle, Descartes' mechanistic philosophy introduced the idea of a reflex to explain the behavior of nonhuman animals. Although his conception of animals treated them as reflex-driven machines, with no intellectual capacities, it is important to recognize that he took mechanistic explanation to be perfectly adequate for explaining sensation and perception — aspects of animal behavior that are nowadays often associated with consciousness. He drew the line only at rational thought and understanding. Given the Aristotelian division between instinct and reason and the Cartesian distinction between mechanical reflex and rational thought, it's tempting to map the one distinction onto the other. Nevertheless, Crowley & Allen (2008) argue that it would be a mistake to assimilate the two. First, a number of authors before and after Darwin have believed that conscious experience can accompany instinctive and reflexive actions. Second, the dependence of phenomenal consciousness on rational, self-reflective thought is a strong and highly doubted claim (although it has current defenders, discussed below).

Although the roots of careful observation and experimentation of the natural world go back to ancient times, studies of animal behavior remained largely anecdotal until long after the scientific revolution. In the intervening period, animals were, of course, widely used in pursuit of anatomical, physiological, and embryological questions, and vivisection was carried out by such luminaries as Galen. Whether or not Descartes himself practiced vivisection (his own words indicate that he did), the mechanists who followed him used Descartes' denial of reason and a soul to animals as a rationale for their belief that live animals felt nothing under their knives.

A few glimmers of experimental approaches to animal behavior can be seen in the late 18th century (e.g., Barrington 1773; White 1789), and soon thereafter Frédéric Cuvier worked from 1804 until his death in 1838 on the development of sexual and social behavior in captive mammals. By the mid 19th century Alfred Russel Wallace (1867) was arguing explicitly for an experimental approach to animal behavior, and Douglas Spalding's (1872) experiments on instinctual feeding behaviors in chicks were seminal. Still, the emergence of experimental approaches had very little to say about consciousness per se, though Spalding's work can be seen as a contribution to the discussion about instinct and reason.

In the same vein of instinct vs. reason, Darwin in the Origin of Species wrote, “It is a significant fact, that the more the habits of any particular animal are studied by a naturalist, the more he attributes to reason, and the less to unlearnt instinct” (1871, Book I, p.46). He devoted considerable attention in both the Origin and in the Descent of Man to animal behavior, with the obvious goal of demonstrating mental continuity among the species. To make his case, Darwin relied heavily on anecdotes provided by his correspondents — a project infamously pursued after Darwin's death by his protégé George Romanes (1882). Darwin also carried out experiments and was a keen observer, however. In his final work he describes experiments on the flexibility of earthworm behavior in manipulating leaves, which he took to show considerable intelligence (Darwin 1881; see also Crist 2002).

The idea of behavioral flexibility is central to discussions of animal mind and consciousness. Descartes' conception of animals as automata seems to make phenomenal consciousness superfluous at best — a connection whose philosophical development was traced by T.H. Huxley (1874). Huxley reported a series of experiments on a frog, showing very similar reflexive behavior even when its spinal cord had been severed, or large portions of its brain removed. He argued that without a brain, the frog could not be conscious, but since it could still do the same sort of things that it could do before, there is no need to assume consciousness even in the presence of the entire brain, going on to argue that consciousness is superfluous. (The argument is somewhat curious since it seems to show too much by making the brain itself superfluous to the frog's behavior!)

Still, for those (including Huxley) who became quickly convinced of the correctness of Darwin's theory of evolution, understanding and defending mental continuity between humans and animals loomed large. In his Principles of Psychology (1890), William James promoted the idea of differing intensities of conscious experience across the animal kingdom, an idea that was echoed by the leading British psychologist of his day, Conwy Lloyd Morgan in his 1894 textbook An Introduction to Comparative Psychology. Morgan had been very skeptical and critical of the anecdotal approach favored by Darwin and Romanes, but he came around to the Darwinian point of view about mental continuity if not about methodology. To address the methodological deficit he introduced his “double inductive” method for understanding the mental states of animals (Morgan 1894). The double induction consisted of inductive inferences based on observation of animal behavior combined with introspective knowledge of our own minds. At the same time, to counteract the anthropomorphic bias in the double inductive method, Lloyd Morgan introduced a principle now known as Morgan's canon: “in no case may we interpret an action as the outcome of the exercise of a higher psychical faculty, if it can be interpreted as the outcome of the exercise of one which stands lower in the psychological scale.” (Lloyd Morgan 1894, p.53).


Lloyd Morgan's Double Induction Method from his 1894 textbook

Even though the double inductive method is now mainly of historical interest, Morgan's canon lives on. Questions about quite what the canon means and how to justify it are active topics of historical and philosophical investigation (e.g., Burghardt 1985; Sober 1998, 2005; Radick 2000; Thomas 2001). The questions include what Lloyd Morgan means by ‘higher’ and ‘lower’, to what extent the principle can or should be justified by evolutionary considerations, and whether the canon collapses to a principle of parsimony, a version of Ockham's razor, or some general principles of empirical justification. Despite current uncertainty about what it really means, Morgan's canon, interpreted (or, perhaps, misinterpreted; Thomas 2001) as a strong parsimony principle, served a central rhetorical role for behavioristic psychologists, who sought to eliminate any hint of Cartesian dualism from comparative psychology.

Behaviorism dominated American psychology in the early part of the 20th century, beginning with Thorndike's (1911) experiments on animals learning by trial and error to escape from the “puzzle boxes” that he had constructed. But even Thorndike's famous “law of effect” refers to the animal's “satisfaction or discomfort” (1911, p.244). It was with the radical anti-mentalism of John B. Watson (1928) and B.F. Skinner (1953), both of whom strongly rejected any attempts to explain animal behavior in terms of unobservable mental states, that American psychology became the science of behavior rather than, as the dictionary would have it, the science of mind and behavior.

At the same time, things were progressing rather differently in Europe, where ethological approaches to animal behavior were more dominant. Ethology is part natural history with an emphasis on fieldwork and part experimental science conducted on captive animals, reflecting the different styles of its two seminal figures, Konrad Lorenz and Niko Tinbergen (see Burkhardt 2005). Initially, “innate” behaviors were the central focus of Lorenz's work. According to Lorenz, it is the investigation of innate behaviors in related species that puts the study of animal behavior on a par with other branches of evolutionary biology, and he demonstrated that it was possible to derive the phylogenetic relations among species by comparing their instinctive behavioral repertoires (Lorenz 1971a). In pursuing this direction, Lorenz and Tinbergen explicitly sought to distance ethology from the purposive, mentalistic, animal psychology of Bierens de Haan and the lack of biological concern they detected in American comparative psychology (see Brigandt 2005). Like Lloyd Morgan, the ethologists rejected Romanes anecdotal approach, but they also criticized Lloyd Morgan's subjectivist approach.

In the 1970s, Donald Griffin, who made his reputation taking careful physical measurements to prove that bats use echolocation, made a considerable splash with his plea for a return to questions about animal minds, especially animal consciousness. Griffin (1978) coined the term “cognitive ethology” to describe this research program. Fierce criticism of Griffin emerged both from psychologists and classically trained ethologists (Bekoff & Allen 1997). Griffin emphasized behavioral flexibility and versatility as the chief source of evidence for consciousness, which he defined as “the subjective state of feeling or thinking about objects and events” (Griffin & Speck 2004, p. 6). In seeing subjectivity, at least in simple forms, as a widespread phenomenon in the animal kingdom, Griffin's position also bears considerable resemblance to Lloyd Morgan's. Burghardt reports that “considerable discomfort with subjectivism” (Burghardt 1985, p. 907) arose during the Dahlem conference that Griffin convened in an early discipline-building exercise (Griffin 1981). Griffin's subjectivist position, and the suggestion that even insects such as honeybees are conscious, seemed to many scientists to represent a lamentable return to the anthropomorphic over-interpretation of anecdotes seen in Darwin and Romanes. This criticism may be partly unfair in that Griffin does not repeat the “friend-of-a-farmer” kinds of story collected by Romanes, but bases his interpretations on results from the more sophisticated scientific literature that had accumulated more than a century after Darwin (e.g., Giurfa et al. 2001). However, the charge of over-interpretation of those results may be harder to avoid. It is also important to note the role played by neurological evidence in his argument, when he concludes that the intensive search for neural correlates of consciousness has not revealed “any structure or process necessary for consciousness that is found only in human brains” (Griffin & Speck 2004). This view is widely although not universally shared by neuroscientists.