Pdf/133/1/29/1828756/001152604772746675.Pdf by Guest on 25 September 2021

Daniel John Povinelli

Behind the ape’s appearance: escaping anthropocentrism

in the study of other minds Downloaded from http://direct.mit.edu/daed/article-pdf/133/1/29/1828756/001152604772746675.pdf by guest on 25 September 2021

Look at Megan. Not just at her distinc- dedicated his life to studying these tively chimpanzee features–her accen- remarkable animals–entertain the pos- tuated brow ridge, her prognathic face, sibility that their minds are, in profound her coarse black hair–but at the totality respects, radically different from our of her being: her darting eyes, her slow, own? How can I challenge the received studied movements, the gestures she wisdom of Darwin–con½rmed by my makes as her companion, Jadine, passes own initial impressions–that the mental nearby. Can there be any doubt that be- life of a chimpanzee is best compared to hind certain obvious differences in her that of a human child? appearance resides a mind nearly identi- Actually, it’s easy: I have learned to cal to our own? Indeed, is it even possi- have more respect for them than that. ble to spend an afternoon with her and I have come to see that we distort their not come to this conclusion? Upon re- true nature by conceiving of their minds flection, you will probably acknowledge as smaller, duller, less talkative versions that her mind is not identical to ours. of our own. Casting aside these insidious “But surely it’s not qualitatively differ- assumptions has been dif½cult, but it has ent, either,” you will still insist. “I mean, allowed me to see more clearly that the it’s obvious from watching her that we human mind is not the gold standard share the same kind of mind.” against which other minds must be Faced with the overwhelming similari- judged. For me it has also illuminated ty in the spontaneous, everyday behavior the possibility of creating a science that of humans and chimpanzees, how can is less contaminated by our deeply an- someone like me–someone who has thropocentric intuitions about the nature of other minds. Daniel John Povinelli is Louisiana Board of Re- gents Endowed Professor of Science at the Univer- The best available estimates suggest sity of Louisiana at Lafayette, and director of the that humans and chimpanzees originat- Cognitive Evolution Group and the Center for ed from a common ancestor about ½ve Child Studies. His latest book is “Folk Physics for or six million years ago.1 This is reflected Apes: The Chimpanzee’s Theory of How the 1 Galina V. Galzko and Masatoshi Nei, “Esti- World Works” (2000). mation of Divergence Times for Major Lineages of Primate Species,” Molecular Biology and Evolu- © 2004 by the American Academy of Arts tion 20 (2003): 424–434. & Sciences

Dædalus Winter 2004 29 Daniel John in estimates of our genetic similarity: we that our minds were 75 percent chim- Povinelli share, on average, about 98.6 percent of panzee? on learning our total nucleotide sequence in com- No, such coarse genetic comparisons mon. This statistic seems impressive. will hardly suf½ce to help us understand After all, such biological af½nity would the complex similarities and differences appear to be the ½nal nail in the cof½n that exist between the mental lives of of the notion that there could be any humans and chimpanzees. However, radical mental differences between in a climate where certain highly visible them and us: if chimpanzees and experts have radically anthropomor- 3 humans share 98.6 percent of their phized chimpanzees, such statistics are Downloaded from http://direct.mit.edu/daed/article-pdf/133/1/29/1828756/001152604772746675.pdf by guest on 25 September 2021 genetic material, then doesn’t it follow heralded as establishing once and for all that there ought to be an extraordinarily that chimpanzees are, at the very least, high degree of mental similarity as well? mentally equivalent to two- or three- This idea has been paraded so frequently year-old human children, and should through the introductory paragraphs of therefore be granted human rights.4 both scholarly journal articles and the A few obvious biological facts may be popular press alike that it has come to worth noting here. To begin, it was the constitute a melody of sorts; an anthem human lineage, not the chimpanzee one, that if not sung raises doubts as to one’s that underwent radical changes after our allegiance to the cause of defending the respective geneologies began to diverge chimpanzee’s dignity. from their common ancestor. Since this But what does this 98.6 percent statis- split, humans have resculpted their bod- tic really mean? It should be of immedi- ies from head to toe–quite literally, in ate interest that it is almost invariably fact; as our lineage became bipedal, misreported. We do not share 98.6 per- the pelvis, the knee, and the foot were cent of our genes in common with chim- all drastically reshaped, with modi½ca- panzees; we share 98.6 percent of our tions in the hand (including new mus- nucleotide sequence. A single nucle- cles) soon following. To top it all off, otide difference in a string of four hun- we ultimately tripled the size of our dred may code for a different allele. brain, with disproportionate increases Furthermore, as the geneticist Jonathan probably occurring in the seat of higher Marks has pointed out in lucid detail, cognitive function, the prefrontal cortex. the 98.6 percent statistic has so little Oh yes, and at some point during all of grounding in the average mind that con- this (no one knows exactly when), natu- fronts it, as to render it essentially mean- ral language–perhaps the most notice- ingless.2 We might, after all, share 50 percent of our nucleotide sequences in 3 For examples, see Sue Savage-Rumbaugh, common with bananas and broccoli. Kanzi: The Ape at the Brink of the Human Mind But what on earth does it mean to say (New York: John Wiley & Sons, 1994); Jane Goodall, Through a Window (Boston: Houghton that we are 50 percent the same as a Mifflin, 1990); Roger Fouts, Next of Kin (New vegetable? I don’t know about you, but York: William Morrow and Co., 1997). I doubt my mind is 50 percent identical to that of the garden pea. And so what 4 Steven M. Wise, Rattling the Cage: Toward Le- would it mean, exactly, if we discovered gal Rights for Animals (Cambridge, Mass.: Per- seus Books, 2000); Paola Cavalieri and Peter 2 Jonathan Marks, What It Means to Be 98% Singer, eds., The Great Ape Project: Equality Be- Chimpanzee (Berkeley: University of California yond Humanity (New York: St. Martin’s Press, Press, 2002). 1993).

30 Dædalus Winter 2004 able of human adaptations–emerged as brains–of humans and chimpanzees. Behind well. So, exactly how similar are the brains the ape’s appearance In contrast, chimpanzees have proba- of humans and chimpanzees? After all, bly changed relatively little from the if we knew that, couldn’t we directly ad- common ancestor they shared with us dress the question of their mental sim- about ½ve million years ago. Indeed, ilarity? Well, it would be a start, any- of all of the members of the great ape/ how. Unfortunately, comparisons of the human group who shared a common brains of humans and apes have tradi- ancestor about ½fteen million years ago, tionally been limited to gross considera-

none, indeed, has diverged as much as tions such as size and surface features Downloaded from http://direct.mit.edu/daed/article-pdf/133/1/29/1828756/001152604772746675.pdf by guest on 25 September 2021 humans. A simple thought experiment (such as lobes and sulcus patterns). may help to put this point into perspec- Remarkably, the details of the internal tive: line up all of the species in ques- organization of human and great ape tion–gorillas, orangutans, chimpan- brain systems and structures have been zees, bonobos, humans–and one of largely ignored, in part because it’s so them immediately stands out. Guess dif½cult to study these brains, but also which one? because most neuroscientists have fre- In fact, the more we compare humans quently assumed that despite great dif- and chimpanzees, the more the differ- ferences in size, all mammalian brains ences are becoming apparent. Even ge- are organized pretty much the same. neticists are starting to catch up with Fortunately, even this is beginning the reality of these differences. New re- to change. For example, Todd Preuss, search has shown that rough similarity working at the University of Louisiana, in our nucleotide sequences obscures recently made a startling discovery the fact that the same genes may have while comparing the brains of humans dramatically different activity levels in and chimpanzees. Turning his attention the two species. So even where humans away from the frontal lobes, his previous and chimpanzees share genes in com- area of research, Preuss decided to take mon, it turns out that there are what can a look at the primary visual cortex (V1), only be described as major differences in the area of the cerebral cortex that is the gene expression–that is, whether, when, ½rst way station into the processing of and for how long genes are actually visual information. The organization of working to produce the proteins for this area of the brain has been assumed which they code.5 This is the real stuff to be nearly identical across primates. of genetic comparison, and it casts our But there, in the middle of V1, Preuss crude genetic similarity to the garden and his colleagues uncovered a distinc- pea in a wholly different light. tively human specialization–a kind of What makes these differences in gene neural architecture not found even in expression signi½cant is that they ulti- chimpanzees.6 Preuss speculates that mately manifest themselves as differ- this specialization involves modi½ca- ences in the bodies–including the tions of the pathways related to spatial vision and motion processing. But, re- 5 Wolfgang Enard et al., “Intra- and Inter- speci½c Variation in Primate Gene Expression gardless of what it is for, it suggests that Patterns,” Science 296 (2002): 341–343; Mario Cáceres et al., “Elevated Gene Expression Lev- 6 Todd M. Preuss et al., “Distinctive Compart- els Distinguish Human from Non-Human Pri- mental Organization of Human Primary Visual mate Brains,” Proceedings of the National Acade- Cortex,” Proceedings of the National Academy of my of Sciences 100 (2003): 13030–13035. Sciences 96 (1999): 11601–11606.

Dædalus Winter 2004 31 Daniel John we need to rethink brain evolution in a opposed to, “How does thinking differ Povinelli on way that’s consistent with neo-Darwin- across species?” (the latter being a learning ian theory: similarity and difference decidedly more evolutionarily minded among species as comfortable bedfel- question). lows; a state of affairs accomplished by Assuming that chimpanzees and other weaving in new systems and structures species have mental states (a point I take alongside the old. “If we ½nd such differ- for granted), it seems to me that a more ences in the middle of the primary visual productive question to ask is, “What are cortex,” Preuss recently remarked to me, their mental states about?” Or, put an-

“just imagine what we’re going to ½nd other way, “What kinds of concepts do Downloaded from http://direct.mit.edu/daed/article-pdf/133/1/29/1828756/001152604772746675.pdf by guest on 25 September 2021 when we start looking elsewhere.” they have at their disposal?” It would Some may be surprised (or even stand to reason that the mental states of afraid) to learn of such differences be- chimpanzees, ½rst and foremost, must tween humans and our nearest living rel- be concerned with the things most rele- atives. After several decades of being fed vant to their natural ecology–remem- a diet heavy on exaggerated claims of the bering the location of fruit trees, keeping degree of mental continuity between hu- an eye out for predators, and keeping mans and apes, many scientists and lay- track of the alpha male, for instance. persons alike now ½nd it dif½cult to con- And so surely chimpanzees form confront the existence of radical differences. cepts about concrete things–things like But then, in retrospect, how viable was trees, facial expressions, threat vocaliza- the idea of seamless mental continuity in tions, leopards, and the like. But what the ½rst place? After all, it tended to por- about more abstract concepts? Con- tray chimpanzees as watered-down hu- cepts like ghosts, gravity, and God? mans, not-quite-½nished children. De- Admittedly, to use the term ‘concept’ spite the fact that aspects of this notion as loosely as I have will require the indul- can be traced straight to Darwin, it is an gence of certain scholars. But perhaps evolutionarily dubious proposition, to some progress can be made by noting say the least. that every concept is at least somewhat abstract if it extends beyond a particular If there are substantial differences be- example. For instance, if one has a no- tween the mental abilities of humans tion of an apple that is not limited to a and chimpanzees, in what areas are they single instance of that apple, then one likely to exist? Over the past couple of has made a generalization, and thus a thousand years, many potential rubicons kind of abstraction. Given that it has separating human and animal thinking been known for decades or more that have been proposed. Some of these have chimpanzees and many other species been particularly unhelpful, such as the form such abstractions,8 this cannot be radical behaviorists’ forgettable proposi- a de½ning feature of human thinking. tion that animals don’t ‘think’ at all (of course, these behaviorists were even 8 Suzette L. Astley and Edward A. Wasserman, skeptical about the existence of human “Object Concepts: Behavioral Research with Animals and Young Children,” in William T. thought!). And, unfortunately, in the O’Donohue, ed., Learning and Behavior Therapy popular imagination the question still (Boston: Allyn and Bacon, 1997), 440–463; appears to be, “Can animals think?”7 as Tom R. Zentall, “The Case for a Cognitive Approach to Animal Learning and Behavior,” 7 Eugene Linden, “Can Animals Think?” Time, Behavioural Processes 54 (2001): 65–78. 22 March 1993.

32 Dædalus Winter 2004 At the risk of oversimpli½cation, let about observable things; but, at the Behind the ape’s me instead propose a distinction be- same time, are radically different, in that appearance tween concepts that refer to objects humans form additional concepts about and events that can be directly observed inherently unobservable things.9 (that is, things that can be detected by Now, I realize that most people would the unaided senses), versus hypothetical not be surprised if it were established entities and processes (things that are beyond doubt that chimpanzees lack a classically unobservable). Thus, I wish concept of God. But what about other, to separately consider all concepts that seemingly more prosaic concepts that

refer to theoretical things: all the things infest our way of thinking about the Downloaded from http://direct.mit.edu/daed/article-pdf/133/1/29/1828756/001152604772746675.pdf by guest on 25 September 2021 that are not directly registered by the world? Consider the way in which we senses, but are merely posited to exist think about the social realm. In interact- on the basis of things we can observe. ing with each other (and with animals, Such concepts permeate our common- for that matter), we use a dual system sense way of thinking: we explain phys- of representation: we understand other ical events on the basis of things like beings both as part of the observable ‘forces’ (supernatural or otherwise) world (they engage in particular move- that we have never actually witnessed, ments of their hands and feet, and and account for the behavior of other their lips form particular contortions as humans on the basis of mental states sounds emerge from their mouths), and we have never seen (e.g., their beliefs, as entities with mental properties–un- desires, and emotions). These concepts observable attributes like emotions, in- serve as the bedrock for some of our tentions, desires, and beliefs. most fundamental explanations for why The proposal is that, in contrast to the world works the way it does. humans, chimpanzees rely strictly upon Meanwhile, we can directly contrast observable features of others to forge these sorts of concepts with ones that their social concepts. If correct, it would are derived from things that can be di- mean that chimpanzees do not realize rectly observed: apples and oranges, that there is more to others than their trees, flashes of lightning, facial expres- movements, facial expressions, and hab- sions–even the raising of a hand or the its of behavior. They would not under- sound of a train whistle blowing in the stand that other beings are repositories distance. Concepts about these things of private, internal experience. They share at least one property in common: would not appreciate that in addition they are all derived from the world of to things that go on in the observable macroscopic entities with which the pri- world, there are forever hidden things mary senses directly interact. Without that go on in the private life of the mind. additional justi½cation, I am therefore It would mean that chimpanzees do not asserting a distinction between con- reason about what others think, believe, cepts that refer to observable objects and feel–precisely because they do not and events, and ones that refer to strict- form such concepts in the ½rst place. ly hypothetical ones. 9 This discussion extends several previous o, here’s a proposal: the mental lives descriptions of this hypothesis, for example, S my article with Jesse Bering and Steve Giam- of humans and chimpanzees are similar, brone, “Toward a Science of Other Minds: in that both species form innumerable Escaping the Argument by Analogy,” Cognitive (and in many cases, identical) concepts Science 24 (2000): 509–541.

Dædalus Winter 2004 33 Daniel John Before we get too much further, let of ‘seeing’ (unobservable feature). So, Povinelli on me be honest: I recognize that this pro- the proposal isn’t that chimpanzees use learning posal has troubling implications. For one system and humans use another; one thing, if chimpanzees do not reason both species are purported to rely upon about unobservable entities, then we concepts about the observable proper- would frequently need distinctly differ- ties of others. Instead, the proposal is ent explanations for human and chim- that chimpanzees don’t form additional panzee behavior–even in situations concepts about the unobservable proper- where the behavior looks almost identi- ties of other beings (or the world in gen-

cal. Mind you, we would not need com- eral, for that matter). Downloaded from http://direct.mit.edu/daed/article-pdf/133/1/29/1828756/001152604772746675.pdf by guest on 25 September 2021 pletely different explanations, just ones So, at face value, the proposal I have that are distinctive enough to capture made is worrying. In interpreting what the proposed difference. Nonetheless, would appear to be the exact same be- each time we witnessed a chimpanzee haviors in humans and chimpanzees in engage in a complex social behavior that different ways, I seem to be applying a resembles our own, we would have to double standard. believe that, unlike us, the chimpanzee But is this implication really problem- has only one conceptual system for en- atic, or does it just seem problematic coding and reasoning about what is hap- because it runs counter to some of our pening: a system that invokes concepts most deeply engrained–but fundamen- derived from observable features of the tally flawed–ways of thinking? world. Thus, when chimpanzees deceive each other (which they do regularly), Assume, for a moment, that you have they would never be trying to manipu- traveled back in time to a point when late what others believe, nor what oth- there were no chimpanzees on this plan- ers can see or hear, for constructs like et–and no humans, either. Imagine fur- ‘believing,’ ‘seeing,’ and ‘hearing’ are ther that you have come face to face with already deeply psychological. No, in members of the last common ancestor deciding what to do, the chimpanzee of humans and chimpanzees. Let’s stipu- would be thinking and reasoning solely late that these organisms are intelligent, about the abstracted statistical regulari- thinking creatures who deftly attend to ties that exist among certain events and and learn about the regularities that un- the behaviors, postures, and head move- fold in the world around them. But let ments (for example) of others–what we us also stipulate that they do not reason have called ‘behavioral abstractions.’10 about unobservable things; they have I should note that humans, too, rely no ideas about the ‘mind,’ no notion of heavily upon behavioral abstractions in ‘causation.’ their day-to-day interactions. We must As you return to your time machine be doing so: otherwise upon what basis and speed forward, you will observe new could we attribute additional, psycho- lineages spring to life from this common logical states to others? First, we recog- ancestor. Numerous ape-like species will nize the turn of the head and the direc- emerge, then disappear. As you approach tion of the eyes (observable features), the present day, you will even witness then we ascribe the internal experience the evolutionary birth of modern orang- 10 Daniel J. Povinelli and Jennifer Vonk, utans, chimpanzees, and gorillas. But “Chimpanzee Minds: Suspiciously Human?” amid all of this your attention will be Trends in Cognitive Science 7 (2003): 157–160. drawn to one particular offshoot of this

34 Dædalus Winter 2004 process, a peculiar genealogy that buds Now, is it really troubling to invoke a Behind the ape’s off numerous descendent species. This different explanation for what on the appearance particular lineage has evolved an eye- surface seem to be identical units of catching trick: it habitually stands up- behavior in humans and chimpanzees? right; it walks bipedally. And some of If the scenario I have outlined above is its descendants build upon this trick, correct, then the answer must be, no. capitalizing upon the new opportunities After all, for any given ability that hu- it offers. For reasons that we may never mans and chimpanzees share in com- fully know, tool use and manufacture in- mon, the two species would share a

crease exponentially, language emerges, common set of psychological structures, Downloaded from http://direct.mit.edu/daed/article-pdf/133/1/29/1828756/001152604772746675.pdf by guest on 25 September 2021 brain size triples, and, as more time which, at the same time, humans would passes, human material and social cul- augment by relying upon a system or ture begins to accrete upon the shoul- systems unique to our species. The resid- ders of the lineage’s last surviving mem- ual effect of this would manifest itself in ber: Homo sapiens sapiens. Now, imagine numerous ways: some subtle (such as that as part of this process, this lineage tightly constrained changes in the de- evolved new conceptual structures (in- tails of things to which our visual sys- timately connected to the evolution of tems attend), others more profound language) that allow them to reason (such as the creation of cultural artifacts about things that cannot be observed: like the issue of Dædalus in which you mental states, physical forces, spiritual are now reading these words). deities. I have stipulated all of this so we can So much for theory. What about the confront the following question: If evo- empirical evidence; does it support the lution proceeded in this quite plausible proposal I have just offered? Although it manner, then how would we expect the will not surprise you to learn that I think spontaneous, everyday behavior of hu- it does, I have not always been of this mans to compare to that of chimpan- opinion; I used to believe that any dif- zees? The answer, I think, is that things ferences between humans and chim- would look pretty much the way they do panzees would have to be trivial. But now. After all, humans would not have the results of over two hundred studies abandoned the important, ancestral psy- that we have conducted during the past chological structures for keeping track ½fteen years have slowly changed my of other individuals within their groups, mind. Combined with ½ndings from nor jettisoned their systems for noticing other laboratories, this evidence has that something very different happens forced me to seriously confront the pos- when Joe turns his head toward so-and- sibility that chimpanzees do not reason so, just depending on whether or not his about inherently unobservable phenom- hair is standing on end. No, in evolving a ena. new psychological system for reasoning Let me briefly illustrate this evidence about hypothetical, internal mental with three simple examples: one from states, humans would not have (indeed, the social domain, one from the domain could not have!) abandoned the ancient of physics, and one from the domain of systems for reasoning about observable numerical reasoning. behavior. The new system by de½nition First, what does the experimental evi- would depend upon the presence of old- dence suggest about whether chimpan- er ones. zees reason about mental states? Al-

Dædalus Winter 2004 35 Daniel John though the opinions of experts differ would approach a familiar playmate or Povinelli on (and have swung back and forth over the caretaker to request a food treat using learning past several years), I believe that at pres- their species-typical begging gesture. ent there is no direct evidence that chim- Simple enough. But on the crucial test panzees conceive of mental states, and trials, the chimpanzees were confronted considerable evidence that they do not. with two individuals, only one of whom As an example, consider the well-studied could see them. For example, in one question of whether chimpanzees rea- condition, one caretaker had a blindfold son about the internal, visual experi- covering her mouth, whereas the other

ences of others, that is, of whether had a blindfold covering her eyes. The Downloaded from http://direct.mit.edu/daed/article-pdf/133/1/29/1828756/001152604772746675.pdf by guest on 25 September 2021 they know anything about ‘seeing.’ question was to whom would the chim- To begin, no one doubts that chimpanzee gesture. panzees respond to, reason about, and Not surprisingly, in our trials with hu- form concepts related to the movements man children, even two-year-olds ges- of the head, face, and eyes of others; tured to whoever had the blindfold over these are aspects of behavior that can be her mouth (versus the eyes), probably readily witnessed.11 But what about the because they could represent her inner, idea that another being ‘sees’ things, psychological state (“She can see me!”). that others are loci of unobservable, In striking contrast, our chimpanzees visual experiences? did nothing of the kind. Indeed, in nu- Over the past ten years we have con- merous studies, our chimpanzees gave ducted dozens of studies of juvenile, ad- virtually no indication that they could olescent, and adult chimpanzees to ex- understand ‘seeing’ as an internal expe- plore this question. Perhaps the most rience of others. straightforward of these studies in- With enough trials of any given condi- volved examining how chimpanzees tion the chimpanzees were able to learn understand circumstances under which to select whoever was able to see them; others obviously can or cannot see after enough trials of not being handed a them.12 In these studies, chimpanzees banana when gesturing to someone with were exposed to a routine in which they a bucket over her head, the chimpanzees ½gured out to gesture to the other per- 11 See Daniel J. Povinelli and Timothy J. Eddy, son. Did this mean that they had ½nally “Chimpanzees: Joint Visual Attention,” Psycho- discerned what we were asking them? In logical Science 7 (1996): 129–135; Shoji Itakura, “An Exploratory Study of Gaze-Monitoring in numerous transfer tests in which we pit- Nonhuman Primates,” Japanese Psychological Re- ted the idea that the chimpanzees were search 38 (1996): 174–180; Michael Tomasello, learning about the observable cues (i.e., Brian Hare, and Josep Call, “Five Primate Spe- frontal posture, presence of the face or cies Follow the Visual Gaze of Conspeci½cs,” eyes) against the possibility that on the Animal Behaviour 58 (1998): 769–777. basis of such cues they were reasoning 12 Our laboratory’s empirical research of about who could ‘see’ them, the chim- chimpanzees’ understanding of ‘seeing’ has panzees consistently insisted (through been summarized in my article, “The Minds their behavior) that they were reasoning of Humans and Apes are Different Outcomes about observable features, not internal of an Evolutionary Experiment,” in Susan M. mental states, to guide their choices. Fitzpatrick and John T. Bruer, eds., Carving Our Destiny: Scienti½c Research Faces a New Millenni- In addition to what they learned in um (Washington, D.C.: National Academy of these tests, it also became apparent that Sciences and John Henry Press, 2001), 1–40. chimpanzees come pre-prepared, as it

36 Dædalus Winter 2004 were, to make sense of certain postures. Of course, some have challenged this Behind the ape’s For instance, in our tests they immedi- conclusion, arguing that we need to turn appearance ately knew what to do when confronted up the microscope and develop more with someone facing them versus some- tests that will allow chimpanzees to ex- one facing away, and this ½nding has press their less well-developed under- been replicated in several other labora- standing of such concepts.14 So, for ex- tories.13 “But if they make that distinc- ample, researchers at Emory University tion,” you wonder, “then why do they recently conducted tests in which a perform so differently on the other dominant and a subordinate chimpan-

tests? Is it just because they’re con- zee were allowed to ½ght over food that Downloaded from http://direct.mit.edu/daed/article-pdf/133/1/29/1828756/001152604772746675.pdf by guest on 25 September 2021 fused? How are we to make sense of was positioned in an enclosure between such a puzzling pattern of ½ndings?” them.15 On the critical trials, two pieces Actually, these results are not puzzling of food were positioned equidistant at all if the ability to reason about men- from the animals. The catch was that tal states evolved in the manner that I one piece of food was placed behind an suggested earlier–that is, if humans opaque barrier so that only the subordi- wove a system for reasoning about men- nate could see it. The researchers report tal states into an existing system for rea- that when the subordinate was released soning about behavior. After all, if the into the enclosure, he or she tended to idea is correct, then chimpanzees may head for the food that was hidden from well be born predisposed to attend to the dominant’s view, suggesting, per- certain postures and behaviors related haps, that the subordinate was modeling to ‘seeing’–even though they know the visual experience of his or her domi- nothing at all about such mental states nant rival. per se–precisely because overt features But do such tests really help?16 Do of behavior are the tell-tale indicators of they reveal some weaker understanding the future behavior of others. But when such features are carefully teased apart 14 Michael Tomasello et al., “Chimpanzees Un- derstand Psychological States–The Question to probe for the presence of a mentalistic Is Which Ones and to What Extent,” Trends in construal of others, the chimpanzees Cognitive Science 7 (2003): 153–156, esp. 156. stare back blankly: this is not part of their biological endowment. Thus, if the 15 Brian Hare et al., “Chimpanzees Know evolutionary framework I have sketched What Conspeci½cs Do and Do Not See,” Ani- is correct, neither the chimpanzees nor mal Behaviour 59 (2000): 771–785; see also M. Rosalyn Karin-D’Arcy and Daniel J. Povinelli, the results are ‘confused’; that epithet “Do Chimpanzees Know What Each Other may fall squarely upon the shoulders of See? A Closer Look,” International Journal of we human experimenters and theorists Comparative Psychology 15 (2002): 21–54. who are so blinded by our own way of understanding the world that we are not 16 In a recent analysis of the diagnostic potential of these and other tests, Jennifer Vonk and readily open to the chimpanzee’s way of I (see footnote 10) argued that the logic of cur- viewing things. rent tests with chimpanzees (and other animals) cannot, in principle, provide evidence 13 For example, see Autumn B. Hostetter et al., that uniquely supports the notion that they are “Differential Use of Vocal and Gestural Com- reasoning about mental states (as opposed to munication by Chimpanzees (Pan troglodytes) in behavior alone), and we advocated a new par- Response to the Attentional Status of a Human adigm of tests that may have such diagnostic (Homo sapiens),” Journal of Comparative Psycholo- power. An alternative point of view is provided gy 115 (2001): 337–343. in the companion piece by Tomasello and col-

Dædalus Winter 2004 37 Daniel John of mental states in chimpanzees? These Table 1 Povinelli Theoretical causal constructs and their observ- on are precisely the situations in which learning chimpanzees will be evolutionarily able ‘ambassadors’ primed to use their abilities to form Theoretical Paired observable concepts about the actions of others to concept ‘ambassador’ guide their social behavior. So, for example, they can simply know to avoid food gravity downward object that is out in the open when a dominant trajectories animal is about to be released. “But transfer of force motion-contact-motion sequences still,” the skeptic within you asks, Downloaded from http://direct.mit.edu/daed/article-pdf/133/1/29/1828756/001152604772746675.pdf by guest on 25 September 2021 “that’s pretty smart, isn’t it? The chim- strength propensity for panzees would have to be paying atten- deformation tion to who’s behind the door, and what shape perceptual form that other individual is going to do when the door opens, right?” physical connection degree of contact Fair enough. But that, in the end, is weight muscle/tendon stretch the point: chimpanzees can be intelli- sensations gent, thinking creatures even if they do not possess a system for reasoning about psychological states like ‘seeing.’ A second example of the operation of If it turns out that this is a uniquely hu- what may be a uniquely human capacity man system, this should not detract to reason about unobservables comes from our sense of the evolved intelli- from comparisons of humans’ and gence of apes. By way of analogy, the chimpanzees’ commonsense under- fact that bats echolocate but humans standing of physics. Humans–even don’t, hardly constitutes an intellectual very young children–seem disposed to or evolutionary crisis. assume that there’s more to the physi- In the ½nal analysis, the best theory cal world than what meets the eye. For will be the one that explains both data example, when one ball collides with sets: the fact that chimpanzees reason another, stationary one, and the second about all the observable features of oth- speeds away, even quite young children ers that are associated with ‘seeing’– are insistent that the ½rst one caused and yet at the same time exhibit a strik- the second to move away. Indeed, as ing lack of knowledge when those fea- Michotte’s classic experiments revealed, tures are juxtaposed in a manner that this seems to be an automatic mental they have never witnessed before (i.e., process in adult humans.17 But what is blindfolds over eyes versus over the it, exactly, that humans believe causes the mouth). I submit that, at least for the movement of the second ball? As Hume time being, the evolutionary hypothesis noted long ago, they do not merely rec- I have described best meets this criteri- ognize that the objects touched; that’s on. just a re-description of the observed events.18 No, the ½rst one is seen as hav-

17 Albert Michotte, The Perception of Causality leagues. However, I believe that this view dra- (New York: Basic Books, 1963). matically underestimates the representational power of a psychological system that forms 18 David Hume, Treatise of Human Nature, vols. concepts solely about the observable aspects 1–2, ed. A. D. Lindsay (London: Dent, 1739; of behavior. 1911).

38 Dædalus Winter 2004 ing transmitted something to the second question was whether, when confronted Behind the ape’s object, some kind of ‘force.’ But where is with two new options, they would select appearance this force? Can it be seen? No, it is a the- the one involving genuine physical con- oretical thing. nection as opposed to mere ‘contact.’ In an initial ½ve-year study of ‘chim- Consistent with our ½ndings in other panzee physics,’ we focused our apes’ tests, they did not. Instead, ‘perceptual attention on simple tool-using prob- contact’ seemed to be their operating lems.19 Given their natural expertise concept. The observable property of with tools, our goal was to teach them contact (of any type) was generally suf-

how to solve simple problems–tasks in- ½cient for them to think that a tool could Downloaded from http://direct.mit.edu/daed/article-pdf/133/1/29/1828756/001152604772746675.pdf by guest on 25 September 2021 volving pulling, pushing, poking, etc.– move another object. and then to use carefully designed transfer tests to assess their understanding of Finally, consider the chimpanzee’s nu- why the tool objects produced the effects merical understanding. Over the past they did. In this way, we attempted to decade or so, it has become apparent determine if they reason about things that many species share what Stanislas like gravity, transfer of force, weight, Dehaene has called a ‘number sense’– and physical connection, or merely form the ability to distinguish between larger concepts about spatio-temporal regular- and smaller quantities, even when the ities. To do so, we contrasted such con- quantities being compared occupy iden- cepts with their perceptual ‘ambassa- tical volumes.20 dors’ (see table 1), much in the same way In an attempt to explore the question that we had contrasted the unobservable of numerical reasoning in animals, sev- psychological state of ‘seeing’ against eral research laboratories have trained the observable behavioral regularities apes to match a speci½c quantity of that co-vary with ‘seeing.’ items (say, three jelly beans) with the To pick just one example: we explored appropriate Arabic numeral.21 That they in detail the chimpanzee’s understand- can accomplish this should not be the ing of physical connection–of the idea least bit surprising: humans and chim- that two objects are bound together panzees (and many other species) share through some unobservable interaction the ability to visually individuate ob- such as the force transmitted by the jects. After extensive training, further- mass of one object resting on another, more, the most apt of these pupils have or the frictional forces of one object gone on to exhibit some understanding against another; or conversely, the idea of ordinality (the idea that 5 represents a that simply because two objects are physically touching does not mean there 20 Stanislas Dehaene, The Number Sense (Ox- is any real form of ‘connection.’ We pre- ford: Oxford University Press, 1997). sented our chimpanzees with numerous 21 For this discussion, I rely heavily on the problems, but consider one test in which detailed results from Ai, a twenty-½ve-year-old we ½rst taught them to use a simple tool chimpanzee whose numerical abilities have to hook a ring in order to drag a platform been studied since she was ½ve by a team led by with a food treat on it toward them. Al- Tetsuro Matsuzawa in Kyoto, Japan. See Dora though they learned to do so, our real Biro and Tetsuro Matsuzawa, “Chimpanzee Numerical Competence: Cardinal and Ordinal Skills,” in Tetsuro Matsuzawa, ed., Primate Ori- 19 Daniel J. Povinelli, Folk Physics for Apes (Ox- gins of Human Cognition and Behavior (Tokyo: ford: Oxford University Press, 2000). Springer, 2001), 199–225.

Dædalus Winter 2004 39 Daniel John larger quantity than 4, for example). So, when confronted with a scrambled ar- Povinelli on isn’t this evidence that chimpanzees ray of the numerals 1 to 9, she has the learning have a solid grasp of the notion of the remarkable ability to select them in number? ascending order. Let us scratch the surface a bit, to look But what does it mean that under the at these ½ndings from the perspective I right training regime we can guide a have been advocating. First, do these chimpanzee like Ai into a performance chimpanzees possess a dual understand- that looks, in many but not all respects, ing of numbers–both as associates of like human counting? One possibility

real object sets and as inherently theo- is that a basic number sense–a system Downloaded from http://direct.mit.edu/daed/article-pdf/133/1/29/1828756/001152604772746675.pdf by guest on 25 September 2021 retical things–such that every succes- grounded to individual macroscopic sive number in the system is exactly ‘1’ objects–is widespread among animals, more than the previous number? The and that apes (and other animals) can training data even from Ai, the most use this ability (in concert with their mathematically educated of all chim- other cognitive skills) to ½gure out panzees, suggests that they do not. For ways to cope with the ‘rules’ that example, each time the next numeral humans establish in their tests. In con- was added into her training set, it took trast, the human system for counting (as her just as long to learn its association well as other mathematical ideas) could with the appropriate number of objects be seen as building upon these older sys- as it took with the previous numeral. In tems by reifying numbers as things in other words, there appeared to be little their own right–theoretical things. This evidence that Ai understood the symbols may seem like a subtle and unimportant as anything other than associates of the distinction for some tasks, but it may be object sets. Furthermore, even her dedi- one that leaves the ape mysti½ed when cated mentors suggest that she was not facing questions that treat numbers ‘counting’ at all: with quantities of up as things in their own right. to three or four objects, she performed As a striking example of the distinc- like humans, using an automatic process tion I have been trying to draw, consider (‘subitizing’) to make her judgments; zero, surely one of the purest examples but with larger quantities, instead of that exists of an inherently unobservable counting, it appears as if she was simply entity. If I am right, then zero ought to estimating ‘larger’ or ‘smaller.’ be virtually undetectable by the chim- What about ordinality? When ½rst panzee’s cognitive system. And indeed, tested for her understanding of the rela- the data seem to bear this out.22 For all tive ordering of numbers, Ai exhibited of her training, even Ai does not appear no evidence that this was part of her to have learned to understand zero in conceptual structure. That is, when pre- this sense. True, she (and other animals) sented with pairs of numbers, 1 versus 8, have quickly learned to pick the numeral for example, she did not seem to have 0 in response to the absence of objects any notion that the value of 1 is smaller (something easily explained by associa- than the value of 8–even though she had tive learning processes). But tests of or- been correctly matching these numerals to object sets for years! Of course, after 22 Dora Biro and Tetsuro Matsuzawa, “Use of Numerical Symbols by the Chimpanzee (Pan extended training, Ai did eventually ex- troglodytes): Cardinal, Ordinals, and the Intro- hibit evidence of this ability, and now, duction of Zero,” Animal Cognition 4 (2001): after more than ½fteen years of training, 193–199.

40 Dædalus Winter 2004 dinality involving zero (choosing wheth- And yet I cannot help but suspect that Behind the ape’s er 0 is greater or lesser than 6, for ex- many of you will react to what I have appearance ample) have consistently revealed what said with a feeling of dismay–perhaps I believe might be best described as the loss; a sense that if the possibility I have virtual absence of the concept. Although sketched here turns out to be correct, this training has gradually forced her then our world will be an even lonelier ‘understanding’ of zero into a position place than it was before. But for the further and further down the ‘number time being, at least, I ask you to stay this line,’ even to this day, after thousands of thought. After all, would it really be so

trials, Ai still reliably confuses 0 with 1 disappointing if our ½rst, uncontaminat- Downloaded from http://direct.mit.edu/daed/article-pdf/133/1/29/1828756/001152604772746675.pdf by guest on 25 September 2021 (and in some tasks, with 2 or 3 as well). ed glimpse into the mind of another However one wishes to interpret such species revealed a world strikingly dif- ½ndings, they are certainly not consis- ferent from our own; or all that surpris- tent with an understanding of the very ing if the price of admission into that essence of zero-ness.23 world were that we check some of our most familiar ways of thinking at the Our work together is done. To the door? No, to me, the idea that there may best of my ability I have laid out the case be profound psychological differences for believing that chimpanzees can be between humans and chimpanzees no bright, alert, intelligent, fully cognitive longer seems unsettling. On the con- creatures, and yet still have minds of trary, it’s the sort of possibility that has, their own. From this perspective, it on at least some occasions, emboldened may be our species that is the peculiar our species to reach out and discover one–unsatis½ed in merely knowing new worlds with open minds and hearts. what things happen, but continually driven to explain why they happen, as well. Armed with a natural language that makes referring to abstract things easy, we continually pry behind appearances, probing ever deeper into the causal structure of things. Indeed, some tests we have conducted suggest that chimpanzees may not seek ‘explanations’ at all.24

23 One might retort that the numeral 0 appeared quite late in human history. But here’s a thought experiment. Return to our imaginary time machine (see above) and travel back to those civilizations that predate the invention of the numeral 0. How dif½cult would it be to teach those adult humans the position occupied by the symbol for zero?

24 Daniel J. Povinelli and Sarah Dunphy-Lelii, “Do Chimpanzees Seek Explanations? Prelimi- nary Comparative Investigations,” Canadian Journal of Comparative Psychology 55 (2001): 187–195.

Dædalus Winter 2004 41