Human “exceptionalism” is for many people an unquestioned assumption. For the religious, it is a God-given fact; for humanists, it is a celebration of our unique mental capacities. No other species has created music, art, literature, or built skyscrapers, or imagined going to the moon and figured out how to go there and how to get back. No other species has found treatments for common illnesses and fatal diseases. We are the only animals that use language to share inner experiences with one another.
Our unique features emerged through changes that made us different from our primate and other mammalian ancestors. The fact is, we continue to change over time. If our species survives long enough, future humans will be different from us, and perhaps new human species, with yet unimaginable capacities, will emerge.
Every species is, by definition, different. We care about our differences because they are ours. But from an evolutionary perspective across the long history of life, our traits are not better or more valuable than those possessed by any other organism.1 They are just different.
One of our purported differences is a source of much debate. And that, of course, concerns the nature of the human mind. To what extent do our mental states overlap with and diverge from those of other species? No one would ever confuse the body of another animal with that of a human. Even our closest primate relatives have bodies that are distinct from ours. Yet we freely attribute mental states similar to those we experience to other animals.
Charles Darwin struggled with this problem as he tried to reconcile his biological theory of evolution with his strong opinions about the mental life of animals. He claimed that there are “no fundamental differences between man and the higher mammals in terms of mental faculties”2 and viewed animal emotions as mental states comparable to those experienced by humans.3 His writings were peppered with free-wheeling comments about animal consciousness based, not on science, but on common sense and folk wisdom—that is, by assuming that what goes on in the mind of a human is similar to what is happening inside the head of other animals in similar situations.
Scientifically we don’t really know what, if anything, other animals experience.
During the Victorian era in which Darwin lived, anthropomorphism was rampant in the young science of animal behavior (in part because of Darwin’s influence), and also in popular culture—the novel Black Beauty, about a horse who narrated his mistreatment by humans, was a best-seller. Darwin’s ideas about the relation of animal bodies to ours was revolutionary, but he was lock-step with common wisdom when it came to animal mentation.4
When asked why he viewed animal behavior in terms of human experience, given that his more standard approach was to trace how humans are like other animals, Darwin responded by saying that it was “more cheerful,” and “less off-putting,” to think of the animals in human terms than to treat humans as having “beastial” qualities.5 Many have commented on Darwin’s short-comings in this area.6 For example, in a history of psychology, Fred Keller pointed out that “Darwin bestowed a mental life upon man’s cousins with a very open hand without the self-critical zeal that marked his biological endeavors.”7
Every scientist is also a layperson, and brings everyday assumptions into the lab. We study psychological processes because we have psychological experiences, and want to know more about them. But in order to understand psychological experiences scientifically we have to go beyond mere intuitions and analogies and do research to uncover how things actually work.
I was once at a dinner where a renowned physicist was present. He dismissed outright my contention that animal consciousness is a really difficult scientific problem, and that scientifically we don’t really know what, if anything, other animals experience. “Of course animals are conscious” he bellowed, and proceeded to talk at length about the behavior of his dog. Now suppose someone from another field told him that quantum physics can’t possibly be right because common sense suggests otherwise. He would certainly not give credence to such a challenge.
Our language is inherently anthropomorphic, and as a result our concepts and thoughts tend to lean in this direction as well. J. S. Kennedy, writing in The New Anthropomorphism, proposes that “Anthropomorphic thinking … is built into us … It is dinned into us culturally from earliest childhood. It has presumably also been ‘pre-programmed’ into our hereditary make-up by natural selection, perhaps because it proved to be useful for predicting and controlling the behavior of animals.”8
If Kennedy is right, we can’t help but be anthropomorphic. This is just part of human nature. Herbert Spencer Jennings, an early 20th-century comparative psychologist whose work on the behavior of single cell protozoa was greatly influenced by Darwin, gives a good example: “If Ameoba were a large animal, so as to come within the everyday experience of human beings, its behavior would at once call forth the attribution to it of states of pleasure and pain, of hunger, desire and the like.”9
Beyond a general tendency toward anthropomorphism, each scientist also comes to the lab with other personal biases and dispositions. The philosopher Bertrand Russell once noted, “All the animals that have been carefully observed have behaved so as to confirm the philosophy in which the observer believed before his observations began.”10
Mahzarin Banaji and Anthony Greenwald explain why it is difficult to guard against mental predisopostions.11 Human nature is such that our biases are not freely available to our conscious minds. And it’s hard to compensate for something you don’t know you have.
The fact is that research on animal behavior pretty much has to start from an anthropomorphic stance. We study things that matter to us. As a result, research on animal behavior often involves stimuli that induce significant experiences in people—stimuli that make us feel fear, pain, or pleasure. Some scientists, including esteemed ones, suggest, like Darwin, that because such stimuli make us feel a certain way, if an animal responds similarly, it must feel what we do. For example, the primatologist Frans de Waal expressed this sentiment when he wrote, “If closely related species act the same, the underlying mental processes are probably the same.”12 And Jane Goodall states, as a matter of fact, that “animals feel pleasure and sadness, excitement and resentment, depression, fear and pain.”13 She “knows” what animals experience because she has seen signifiers of these emotions in their behavior. But if all we had to do to link conscious states like feelings to behavior was to observe behavior, we wouldn’t need arduous scientific research. Mere observation is not sufficient.
We can’t help but be anthropomorphic. This is just part of human nature.
Perhaps such comments reflect an attempt to counter previously prevalent behaviorist views of animals as mindless stimulus-response machines controlled by past conditioning. But few if any psychologists today think of behavior simply being due to conditioning. The human mind, for example, is now commonly thought of as encompassing conscious and non-conscious aspects. And much of what we humans do as we make our way through daily life is believed to be controlled by the so-called “cognitive unconscious.”14 While some cognitively processed information makes its way into the conscious mind, most does not.15
The late consciousness researcher Larry Weiskrantz presciently noted, given that consciousness is not always necessary for human perception and behavior, evidence that animals produce appropriate behavioral responses to visual stimuli does not qualify as evidence that they are conscious of what they are seeing.16 The fact that some, but not all, of our cognitive mechanisms are shared with other animals, means that the choice is not between whether complex animal behavior is due to conditioning or consciousness. Non-conscious cognition is an intermediate source of behavioral control, and consciousness should not be assumed to underlie behavior, even complex behavior, unless non-conscious processes can be ruled out.17
Many find it hard to imagine that these kinds of behaviors can be carried out non-consciously in animals since we humans are usually conscious when we do such things ourselves. But the scientific question in an experiment on humans or animals is not whether the organism has the capacity for consciousness in some general sense, but whether consciousness specifically accounts for the behavior that was studied. If this is not tested, the statement that consciousness was involved is not warranted scientifically.
The philosophical “problem of other minds”18 is sometimes used to justify the conclusion that, since we only have access to our own mind, we don’t really know what is on the minds of other humans. Therefore, the argument goes, claims about animal consciousness are just as justified as claims about human consciousness. But this is not the case.19
In human research, methods are available for distinguishing conscious control of behavior from non-conscious control. For example, visual stimuli can be presented in such a way as to allow or prevent conscious awareness (consciousness is prevented by briefly flashing the stimulus and following it with a longer-lasting stimulus that “masks” the first one).20 In such studies, humans cannot verbally report on the identity of the stimulus (they deny seeing anything). Nevertheless, non-verbal behavioral responses (pointing or pressing buttons) or changes in physiological responses (sweating, pupil dilation, or heart rate) can indicate that the stimulus was meaningfully processed. Because verbal responses (in the sense of a sincere, intentional report, as opposed to an automatically elicited exclamation) can only be given about things that one is aware of, verbal report is the gold standard in human consciousness research.21
The fact that animals can only respond nonverbally means there is no contrasting class of response that can be used to distinguish conscious from non-conscious processes. Elegant studies show that findings based on non-verbal responses in research on episodic memory, mental time travel, theory of mind, and subjective self-awareness in animals typically do not qualify as compelling evidence for conscious control of behavior. Such results are better accounted in “leaner” terms; that is, by non-conscious control processes.22 This does not mean that the animals lacked conscious awareness. It simply means that the results of the studies in question do not support the involvement of consciousness in the control of the behavior tested.
Jane Goodall “knows” what animals experience because she has seen signifiers in their behavior. But mere observation is not sufficient.
Some situations in life are best viewed through a scientific lens, and others not. Alexandra Horowitz has examined people’s intuitions about their pets, and has shown that the conscious thoughts and feelings they attributed to their furry friends are typically not scientifically justified, as the pet’s behaviors are more accurately accounted for by cognitive processes that do not require consciousness.23 This does not mean that people should adopt a different, more scientific, approach to their pets. Both people and pets benefit from treating pets as if they have thoughts and feelings, regardless of what science has, or has not, shown.
It is sometimes argued that an anthropomorphic stance toward animal consciousness should be adopted on moral grounds, and scientific evidence should be used to determine which animals deserve moral consideration. But Marian Dawkins eloquently argued that tying the moral issue to the science of animal consciousness weakens rather than strengthens the moral argument, because the question of which animals, other than humans, are conscious, and in which ways, is difficult to determine scientifically. Quoting Thomas Huxley, she notes: “Do not pretend that conclusions are certain that are not demonstrated or demonstrable.” The ethical treatment of animals is an important and complex topic with consequential implications for social norms, including norms about research. But the ethical issues should not be conflated with what counts as criteria for scientifically demonstrating consciousness. These are not the same kinds of questions.
Nick Humphrey, a scientist who turned into a philosopher, once made a rather strange suggestion, given his earlier career: “Away with critical standards, tight measurements and definitions. If an anthropomorphic explanation feels right, try it, and see; if it doesn’t feel right, try it anyway.”24 But standards, measurements, and definitions are not optional. They are what elevate science above commonsense intuitions.
Some use the term “anthropodeniers” for those who suggest caution in making claims about conscious states in animals.25 Are they drawing a comparison with distinctly anti-science “climate-change deniers”? This would be odd, given that the so-called “anthropodeniers” are the ones demanding more rigorous scientific standards. But skeptical researchers, myself included, are not denying the existence of animal consciousness. Instead, we are simply urging that the standard scientific practice of clearly distinguishing data collected in an experiment from the researchers speculations about what that data might mean, be adhered to in studies of animal consciousness.
Some of the problems that can result from confusing conscious and nonconscious control of behavior are illustrated by examples from my own area of research on how the brain detects and responds to danger. It has long been believed that the conscious experience of fear arises out of the brain region called the amygdala. This region is part of our mammalian legacy,26 and it has been assumed, since Darwin, that animals and humans have similar emotions because we have inherited the emotional aspects of our brain from them.27 The amygdala fear center idea thus fits not only with folk wisdom and common sense, but also a venerable scientific legacy. It is so natural and plausible that it has gone unquestioned, and has come to be seen as an established scientific fact, and even as dogma.
But there is a problem. Just because, in the presence of danger (a snake or mugger), a human typically consciously feels fear and also freezes or flees, does not mean that the experience of fear caused the behavior. Correlation does equal causation.
An alternative view that I,28 and other like-minded scientists,29 adhere to is that the conscious experience of fear is not a product of the amygdala circuits that control body responses when in danger. The amygdala is indeed responsible for the responses, but it is not responsible for the conscious experience of fear itself. Its job in situations of danger is to detect and respond to threats, not to make fear. Although amygdala activation does not produce fear, consequences of amygdala activity in the brain and body nevertheless impact the experience of fear, making it more intense and prolonging it in time.30
If the fear center idea is not correct, how does fear itself arise? Considerable evidence suggests that human conscious experiences, possibly even of emotions like fear,31 are assembled by cognitive circuits involving the prefrontal cortex.32 For example, when people can report on what a visual stimulus is, visual cortex and lateral areas of prefrontal cortex are both active. But when the stimuli are masked, and not reportable, only the visual cortex is active. Lateral prefrontal cortex is of interest because the cognitive processes underlying working memory depend on this region, and the information we are conscious of at any one moment is thought to be the information represented in working memory.
Lateral prefrontal areas implicated in consciousness in humans are also found in the great apes and monkeys, but do not exist in other mammals and non-mammalian vertebrate species.33 Yet, the human prefrontal cortex has cellular, molecular, and genetic properties not present in primates, including other apes. In addition, the human prefrontal cortex has circuits within its frontal pole region that do not exist in any other animal.34
The frontal pole is especially important for several reasons. Given that its main connections are with “higher-order” areas involved in conceptual processing and memory, it is believed to represent an especially high level of conceptual processing in the human brain.35 Studies have also specifically implicated the frontal pole in subjective awareness,36 and in conceptual awareness of one’s self as a central component of an experience.37
The neural mechanisms existing in each species determine what kind of cognitive capacities they possess. The unique features of human prefrontal cortex may well contribute to obvious differences in cognitive capabilities between humans and other animals.38 Mechanisms present in other animals may endow them with their own kinds of experiences. But without the mechanisms we have they are unlikely to have the kinds of experiences we do.
While we do not scientifically know what, if anything, other animals actually experience, perhaps we can use scientific research to consider what they might be capable of, given what we know about consciousness and cognition in the human brain. But to do this, we may need a more subtle view of consciousness than the one-size-fits-all monolithic view typically called upon. In this regard, an insightful perspective by psychologist Endel Tuvling may be useful.39
Tulving distinguished between noetic and autonoetic consciousness. Noetic consciousness, he proposed, is the awareness of facts—this is food, that is dangerous, a potential mate is present. Autonoetic consciousness, on the other hand, he said, is the awareness that YOU are the one having the experience. The latter kind of awareness requires a sense of self in time. This is not simply the ability to make a decision that has an impact on future behavior. It instead involves the ability to engage in mental time travel—to envision yourself with a personal past and a hypothetical future (or futures). Tulving suggested that while other animals can engage in future oriented behaviors,40 and may have noetic experiences, only humans have autonoetic consciousness.41
These various ideas coalesce around the conclusion that the human ability for reflective self-awareness and mental time travel may bestow on us a distinct form of conscious experience, one in which our self is central. Not the self as an object (awareness of body states) but the self as a subject (this thought or feeling is mine). And unique features of the human prefrontal cortex may account for this.
Even if other primates lack autonoetic consciousness, they may nevertheless be capable of some form of noetic awareness made possible by those aspects of lateral prefrontal areas shared with humans. This would allow them to have complex knowledge, and perhaps conscious awareness, of stimuli and situations. If other mammals have some kind of conscious awareness, their lack of both lateral prefrontal areas and the frontal pole makes it likely it is a more primitive form, possibly a simpler kind of notetic awareness, or perhaps a non-cognitive form along the lines of a core consciousness related to body awareness, as proposed Antonio Damasio and Jaak Pankseep.42
The difficulty in scientifically measuring consciousness in animals means that we may never truly know for certain what goes on in their minds.43 But maybe this is not the most important question scientifically. Perhaps we should be more focused on cognitive and behavioral capacities that are clearly shared with, and measurable in, other animals. Some of these shared capacities have clearly contributed to the evolution of our kind of consciousness, and may make possible some form of awareness in other animals, even if the capacities they possess do not make them conscious in the way we are.
Joseph LeDoux is the author of The Deep History of Ourselves: The Four-Billion-Year Story of How We Got Our Brains. He is the Henry and Lucy Moses Professor of Science, and Professor of Neural Science, Psychology, Psychiatry, and Child and Adolescent Psychiatry at New York University, where he directs the Emotional Brain Institute. His books include Anxious, Synaptic Self, and The Emotional Brain.
From the book The Deep History of Ourselves by Joseph LeDoux, published by Viking, an imprint of Penguin Publishing Group, a division of Penguin Random House LLC. Copyright © 2019 by Joseph LeDoux.
Lead photo: Dmussman / Shutterstock
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18. Avramides, A, “Other Minds”, The Stanford Encyclopedia of Philosophy (Summer 2019 Edition), Edward N. Zalta (ed.), https://plato.stanford.edu/archives/sum2019/entries/other-minds/.
19. The “problem of other minds” is a hypothetical philosophical argument, not a scientifically based one. The fact is, as I argue below, no other animal has our kind of brain, especially our kind of prefrontal cortex, and the type of cognition it makes possible. And if the unique aspects of our brain and our cognition are key to our kind of consciousness, then our kind of consciousness should not simply be assumed to be present in other animals.
20. Studies of patients with blindsight have also offered insights into dissociations between conscious and nonconsciosu behavioral control. See Weiskrantz L (1997) Consciousness lost and found: A neuropsychological exploration. New York: Oxford University Press, and Lau HC, Passingham RE (2007) Unconscious activation of the cognitive control system in the human prefrontal cortex. J Neurosci 27:5805-5811.
21. For example, see Rosenthal D (2019) Consciousness and confidence. Neuropsychologia. 2019 May;128:255-265. But verbal reports are not without controversy. Sometimes experiences are fleeting and unreportable. Also, reports become less reliable over time, even over short time spans, since memory is dynamic—it changes by the mere passage of time, or by the accumulation of new experiences. Moreover, people often lack accurate introspective insights into the motivations for why they did what they did. People can be dishonest, especially about personal questions (i.e. about the use of recreational drugs or sexual habits). But, in an experiment, where there is not reason to be deceitful, verbal reports are actually fairly reliable indicators of what a subject is experiencing, as people tend to know what they are conscious of, especially if probed in the moment.
22. Heyes C (2015) Animal mindreading: what’s the problem? Psychon Bull Rev 22:313-327; Heyes C (2016) Blackboxing: social learning strategies and cultural evolution. Philos Trans R Soc Lond B Biol Sci 371. PMC4843607; Penn DC, Holyoak KJ, Povinelli DJ (2008) Darwin’s mistake: explaining the discontinuity between human and nonhuman minds. Behav Brain Sci 31:109-130; discussion 130-178; Penn DC, Povinelli DJ (2007) Causal cognition in human and nonhuman animals: a comparative, critical review. Annu Rev Psychol 58:97-118; Shettleworth SJ (2009) The evolution of comparative cognition: is the snark still a boojum? Behav Processes 80:210-217; Shettleworth SJ (2010) Clever animals and killjoy explanations in comparative psychology. Trends Cogn Sci 14:477-481; Suddendorf T, Corballis MC (2007) The evolution of foresight: What is mental time travel, and is it unique to humans? Behav Brain Sci 30:299-313; discussion 313-251; Suddendorf T, Corballis MC (2010) Behavioural evidence for mental time travel in nonhuman animals. Behav Brain Res 215:292-298; Suddendorf T (2013) The Gap: The Science of What Separates Us from Other Animals. New York: Basic Books.
23. Horowitz A (2016) Being a Dog: Following the dog into a world of smell. New York: Scribner.
24. Humphrey, N. K. (1977). Review of Griffin’s The Question of Animal Awareness. Animal Behaviour, 25, 521-522.
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27. Damasio A, Carvalho GB (2013) The nature of feelings: evolutionary and neurobiological origins. Nat Rev Neurosci 14:143-152; Panksepp J, Biven L (2012) The Archaeology of Mind: Neuroevolutionary origins of human emotions. New York: W. W. Norton & Co.
28. LeDoux JE (1996) The Emotional Brain. New York: Simon and Schuster; LeDoux JE (2002) Synaptic Self: How our brains become who we are. New York: Viking; LeDoux J (2012) Rethinking the emotional brain. Neuron 73:653-676; LeDoux JE (2014) Coming to terms with fear. Proc Natl Acad Sci U S A 111:2871-2878; LeDoux JE (2015) Anxious: Using the brain to understand and treat fear and anxiety. New York: Viking; LeDoux JE (2017) Semantics, Surplus Meaning, and the Science of Fear. Trends Cogn Sci 21:303-306; LeDoux JE, Brown R (2017) A higher-order theory of emotional consciousness. Proc Natl Acad Sci U S A 114:E2016-E2025; LeDoux JE, Pine DS (2016) Using Neuroscience to Help Understand Fear and Anxiety: A Two-System Framework. Am J Psychiatry 173:1083-1093.
29. Barrett LF, Russell JA (eds.) (2015) The psychological construction of emotion. New York: Guilford Press; Barrett LF (2017) How emotions are made. New York: Houghton Mifflin Harcourt.
30. Not all scientists agree. Some view fear, not as an experience but as a set of physiological processes that trigger behavioral and physiological responses and also conscious. In this modern day version of behaviorism, conscious fear is not what “fear” is all about. It is just another response. See Fanselow MS, Pennington ZT (2017) The Danger of LeDoux and Pine’s Two-System Framework for Fear. Am J Psychiatry 174:1120-1121; Fanselow MS, Pennington ZT (2018) A return to the psychiatric dark ages with a two-system framework for fear. Behav Res Ther 100:24-29. PMC5794606.
31. LeDoux JE (2015) Anxious: Using the brain to understand and treat fear and anxiety. New York: Viking; LeDoux JE (2017) Semantics, Surplus Meaning, and the Science of Fear. Trends Cogn Sci 21:303-306; LeDoux JE, Brown R (2017) A higher-order theory of emotional consciousness. Proc Natl Acad Sci U S A 114:E2016-E2025; LeDoux JE, Pine DS (2016) Using Neuroscience to Help Understand Fear and Anxiety: A Two-System Framework. Am J Psychiatry 173:1083-1093.
32. Lau H, Rosenthal D (2011) Empirical support for higher-order theories of conscious awareness. Trends Cogn Sci 15:365-373; Odegaard B, Knight RT, Lau H (2017) Should a Few Null Findings Falsify Prefrontal Theories of Conscious Perception? J Neurosci 37:9593-9602. PMC5628405; Fleming SM, van der Putten EJ, Daw ND (2018) Neural mediators of changes of mind about perceptual decisions. Nat Neurosci 21:617-624. PMC5878683.LeDoux JE (2015) Anxious: Using the brain to understand and treat fear and anxiety. New York: Viking; LeDoux JE, Brown R (2017) A higher-order theory of emotional consciousness. Proc Natl Acad Sci U S A 114:E2016-E2025; Brown R, Lau H. and LeDoux JE (2019) Understanding the Higher-Order Theory of Consciousness. Trends Cogn. Sci. 23:754-768.
33. Preuss TM (2011) The human brain: rewired and running hot. Ann N Y Acad Sci 1225 Suppl 1:E182-191. PMC3103088; Preuss TM (2012) Human brain evolution: from gene discovery to phenotype discovery. Proc Natl Acad Sci U S A 109 Suppl 1:10709-10716. PMC3386880; Teffer K, Semendeferi K (2012) Human prefrontal cortex: evolution, development, and pathology. Prog Brain Res 195:191-218.
34. Koechlin E (2011) Frontal pole function: what is specifically human? Trends Cogn Sci 15:241; Semendeferi K, Teffer K, Buxhoeveden DP, Park MS, Bludau S, Amunts K, Travis K, Buckwalter J (2011) Spatial organization of neurons in the frontal pole sets humans apart from great apes. Cereb Cortex 21:1485-1497.
35. Koechlin E (2011) Frontal pole function: what is specifically human? Trends Cogn Sci 15:241; author reply 243.
36. Fleming SM, van der Putten EJ, Daw ND (2018) Neural mediators of changes of mind about perceptual decisions. Nat Neurosci 21:617-624. PMC5878683.
37. Silani, G. et al. (2008) Levels of emotional awareness and autism: an fMRI study. Soc. Neurosci. 3, 97–112.
38. Penn DC, Holyoak KJ, Povinelli DJ (2008) Darwin’s mistake: explaining the discontinuity between human and nonhuman minds. Behav Brain Sci 31:109-130; discussion 130-178; Penn DC, Povinelli DJ (2007) Causal cognition in human and nonhuman animals: a comparative, critical review. Annu Rev Psychol 58:97-118; Suddendorf T. (2018) The Gap: The Science of What Separates Us from Other Animals. New York: Basic Books; MacLean EL (2016) Unraveling the evolution of uniquely human cognition. Proc Natl Acad Sci U S A 113:6348-6354. PMC4988573.
39. Tulving E (2001) The origin of autonoesis in episodic memory. In: The Nature of Remembering: Essays in Honor of Robert G Crowder (Roediger, H. L. et al., eds), pp 17-34 Washington, D.C.: Am Psychol Assoc.
40. Clayton NS, Dickinson A (2010) Mental Time Travel: Can Animals Recall the Past and Plan for the Future? A2 – Breed, Michael D. In: Encyclopedia of Animal Behavior (Moore, J., ed), pp 438-442 Oxford: Academic Press; Raby CR, Clayton NS (2009) Prospective cognition in animals. Behav Processes 80:314-324; Beran MJ, Menzel CR, Parrish AE, Perdue BM, Sayers K, Smith JD, Washburn DA (2016) Primate cognition: attention, episodic memory, prospective memory, self-control, and metacognition as examples of cognitive control in nonhuman primates. Wiley Interdiscip Rev Cogn Sci 7:294-316. PMC5173379.
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42. Damasio A, Carvalho GB (2013) The nature of feelings: evolutionary and neurobiological origins. Nat Rev Neurosci 14:143-152; Panksepp J, Biven L (2012) The Archaeology of Mind: Neuroevolutionary origins of human emotions. New York: W. W. Norton & Co.
43. The philosopher Thomas Nagel famously pointed out that we can never know what the experience of animal is like (Nagel T (1974) What is it like to be a bat? Philosophical Review 83:4435-4450). But just because it’s difficult to demonstrate consciousness in animals does not mean that they lack minds. I don’t know of any serious scientist today who claims that mammals and birds lack minds, if by “mind” we mean the ability to think, plan, and remember. But that is different than the ability to be conscious of one’s own thoughts, plans, and memories. Still, the fact that mammals and birds do have minds does not mean that they have the kind of mind that humans have.