AUTHOR: Hurford, James R. TITLE: The Origins of Meaning SUBTITLE: Language in the Light of Evolution 1 SERIES: Studies in the Evolution of Language PUBLISHER: Oxford University Press YEAR: 2007
Grover Hudson, Department of Linguistics and Germanic, Slavic, Asian and African Languages, Michigan State University
SUMMARY This very readable and satisfying book is an examination of ''pre-linguistic animal concepts and social lives'' which the author supposes ''take us to the brink of modern human language, when the species became for the first time language-ready'' (p. x). The argument, the evidence, and the style encourage the reader to give attention, read on, and look forward with interest to the promised continuation in the next volume. The wealth of studies presented and their informed, insightful, yet cautious interpretation provide probable insight into how and how readily language might have evolved out of animal prelanguage.
This is one of two volumes under under the title _Language in the Light of Evolution_, echoing, says Hurford, Dobzhansky's (1973) title ''Nothing in Biology Makes Sense Except in the Light of Evolution'' - that is, nothing in linguistics as well. The present book ''gives a picture of the semantic and pragmatic aspects of pre-human language-readiness'', and the second, titled _The Evolution of Linguistic Form_, will concern ''the final processes tipping us over the brink of language, the emergence of a shared lexicon and then of complex linguistic forms'' (p. x).
Hurford is well qualified for this ambitious project, having written books on semantics and the typology of number systems, and in recent years several articles anticipating chapters of this book. He is an adaptationist, in the contrast drawn by Chomsky (2006: 175-6) between the 'adaptationist' hypothesis of Darwin, in the words of Pinker (2003: 17) ''that the human language faculty is a complex biological adaptation that evolved by natural selection for communication in a knowledge-using, socially interdependent lifestyle'', and the 'saltationist' hypothesis of Wallace, nowadays often referenced to Chomsky, according to whom (2006: 176) ''the faculty of language'' more probably arose ''through some slight genetic event that brought a crucial innovation'' by which ''the brain was rewired, perhaps by some slight mutation, to provide the operation Merge'' (Chomsky, p. 184; hence, recursion). The former hypothesis, it might be assumed, rejects (perhaps ignores) the distinction claimed within the latter between broad and narrow faculties of language; see discussion by Heine and Kuteva (2007: 10-12), and Hurford's comment (p. xi-xii) that ''the study of language evolution has suffered in the past from insufficient acknowledgement of [the] rich multi-component nature of language...evident in studies which, while sometimes ambitiously labelled 'the evolution of language'... in fact just focus on one domain, such as... syntax (recursion).''
There is an ambiguity in the phrase ''evolution of language'', which has the senses 'appearance of language out of pre-language' and 'development or growth of language subsequent to origin', which arise from different traditions and different data, are pursued in quite different lines of research, and probably appeal to different audiences. The present book, concerned with the appearance sense (specifically the animal precursors of linguistic meaning) might be contrasted with another important 2007 book concerned with the development sense (specifically the development of grammatical morphology): Heine and Kuteva 2007.
The present book has two parts of five chapters each, Part I ''Meaning Before Communication'' and Part II ''Communication: What and Why?'' Hurford says that Part I can be considered to concern semantics and Part II pragmatics (xi). In fact Chapter 1 looks forward to both parts, and Chapter 10 looks back on and forward from both parts. Chapters 2-9 less 5 consist largely of presentation and interpretation of experimental studies on animal cognition or 'meanings', from which Hurford quotes liberally, and I will mention briefly a few of the studies from these chapters, as the best way to give a sense of each. Hurford apologizes for his liberal quoting, but he shouldn't; nothing is more exasperating than paraphrases found to be less accurate and insightful than the originals - and often no shorter!
Chapter 1 ''Let's Agree on Terms'', provides method and assumptions. Hurford says ''we can identify behaviour in animals similar enough to the human behaviour that prompts us to say that humans possess concepts, so it is natural to say that these animals possess concepts too'' (1). He approvingly quotes Fitch (2005) regarding the ''rich cognitive abilities of non-human primates'' which show them as ''having quite complex minds, particularly in the social realm, but lacking a communicative mechanism capable of expressing most of this mental activity''(2). ''Rudimentary concepts, ideas, and thoughts (or something very like them), about things, events, and situations in the world,'' Hurford believes (5-6), ''can reasonably be said to exist in animals' minds, event though they may not ever be publicly expressed in language, or indeed in any kind of communication whatsoever,'' a ''thesis diametrically opposed'' to Wittgenstein's ''The limits of my language mean the limits of my world'', which Hurford says ''would imply that a languageless creature has no world.''
Hurford subscribes to the view ''that the relationship of meaning between language and the world is indirect, and is mediated by the mind, which is host to such things as concepts, ideas, and thoughts'' (5). The opposite view he attributes ''especially [to] formal semantics, which is embarrassed to speculate about what might go on inside people's heads.'' For the 'materialist' argument, perhaps instead of formal semanticists see Dennett (1991).
Chapter 2, ''Animals Approach Human Cognition'', argues that animals have concepts including that of animacy, 'transitive inference' (A>B, B>C so A>C), and the distinction of declarative vs. imperative. Hurford asserts that ''any claim of resemblance between an animal concept and a human concept is based on their apparent extensions in the world'' (20), so he reasonably doubts the claim of Wittgenstein that ''if a lion could talk, we could not understand him'' (21). Lions would certainly talk about our shared world. Even pigeons appear to conceive of pictures as belonging to 'schools', categorizing ''Cezanne and Renoir as Monet school'', and ''paintings by Braque and Matisse as... Picasso school'' (23). Signing chimpanzees famously use abstract and symbolic (arbitrary) signs to categorize things as 'same' and 'different' (26), and the celebrated parrot Alex 12 of 15 times correctly answers the question ''What's same?'' to a list of objects on a tray having color, size, shape differences, and ''What color / shape?''
These Hurford apparently considers to be 'pre-concepts', because ''concepts should be stimulus free..., not completely involuntary or reflexive or automatic'' (29). Furthermore, ''many of these results... describe what animals can do, if pushed'', having not yet ''started to move along the road to language''. It isn't hard to believe that tamarins have the pre-concept 'animate', evidenced in their reactions to ''four different kinds of object in a novel location after the object had moved (or been moved) out of sight...[O]nly one type, the animate ones, such as live frogs and mice, evoked no apparent surprise (as measured by looking time) when they appeared in a novel location'' (42).
''The vervet 'leopard' alarm call is the conjunction of both _There is a leopard nearby_ (the declarative or indicative aspect) and _Run up a tree_ (the procedural or imperative aspect)'' (61), and Hurford appears to argue that this is related to ''the distinction in public communication between declarative and imperative acts, and the sentence-types conventionally associated with them in the languages of the world has...ancient roots in the co-involvement (in varying proportions) of sensory and motor components in primitive proto-concepts'' (64). Mirror-neurons, by which ''the brain of an observing animal [is] in the same kind of partly similar state to that of the observed animal'', suggest to Hurford ''the beginnings of the kind of empathy required in communication at the level of human language'' (61).
Chapter 3, ''A New Kind of Memory Evolves'', argues for ''the faint beginnings'' in some animals of ''an ability to store two kinds of information, semantic and episodic'' (87). ''Episodic memory comes onstream after the beginnings of language in normal children. But it also seems that having a language is not a prerequisite''; Helen Keller, at least, had memories of her pre-linguistic life (69). A chimpanzee led a person to places where it had seen food hidden days earlier, and gorillas similarly, at least 24 hours later (72). Rats return, after ''a little while'', to where they broke off search for food in a maze, and know which arms of the maze they have already searched. The more arms to the maze, the better their memory: they seem to have not just retrospective but prospective memory, having no need to remember so well if the maze is simple (77).
Chapter 4, ''Animals Form Proto-propositions'', argues ''that non-human animals are capable of representing propositions, which do respect a separation between logical predicate and argument'', and that deictic reference is rudimentarily present in pointing. Hurford argues that ''humans and a range of animals'' have ''strikingly similar basic (i.e. non-linguistic) numerical abilities'', with a ''primitive limit of about four'' (91-2) (reducing by 3 Miller's (1956) ''magical number 7'').
Animal prelinguistic propositions are said to be based on two aspects of the visual system, in which the 'where-stream', dorsal pathway, ''takes signals from the retina, via several intermediate stations, to posterior parietal cortex, where motor responses are triggered directing saccades...or head-turning'', which brings an object into focal vision. ''Now the 'what stream', ventral pathway, kicks in. Information from the retina is also routed, by the ventral stream, to the infero-termporal cortex and beyond, where it is acted upon by the kinds of classificatory mechanisms'' (100). ''An animal seeing a lizard on a rock globally perceives an 'on-ness situation'... ON or some other appropriate translation, is a one-place predicate applying to the whole situation or scene, and...the rock and the lizard can be expressed by individual (one-place) properties of each'' (105). Local attention converts scenes received in global attention into one-place predicate-object relations.
Chapter 5, ''Towards Human Semantics'' develops formalities of the argument for animal propositions, simplified from those of formal semantics, so that BRUTUS(x) & CAESAR(y) & STAB(x,y) is [STAB [PATIENT CAESAR] [AGENT BRUTUS] ] (147); i.e, variables such as x and y and orderedness of variables (vs. roles as predicates) are thought unnecessary or obtuse, for us as well as animals. (Hurford has boxes for the square brackets used here.) Regarding the hypothetical animal scene [THREE [COW] [COW] [COW] ], Hurford says ''the two-level outer/inner distinction, corresponding to objects in a scene'', is ''the only iconic aspect of this notation'' - but the repetition of COW is also iconic.
''Animals' mental representations of scenes and events are rooted in perception. It follows that concepts that are not rather directly based on perception (or proprioception) will have no terms for them'', for example definite/indefinite, active/passive (154), and nominal/verbal expression; no difference between objects and events (158), or between subjects and predicates (162); x destroyed y = x's destruction of y, and MARY(x) & SCRATCH(x) is just [MARY SCRATCH]. With the simplified notation, ''evolutionary continuity between non-humans and humans becomes easier to envisage'' (164).
Part 2, ''Communication: What and Why?'' concerns the interpersonal bases of animal prelinguistic meaning, i.e., 'pragmatics' (in contrast to 'semantics' of Part 1). The argument is that animal societies had to evolve trust, and reason to believe that talk would be worthwhile; as such, talk was selective. Hurford notes that both Part I ''exploring prior representational systems in relation to human semantics, and [Part II] exploring the communicative abilities of animals'' (177), give support, respectively, to the Chomskian notion of language as a representational system, and the tradition of language as communication.
Chapter 6, ''Communication by Dyadic Acts'', is about 'non-referring' utterances, involving only a sender and receiver. ''A form of communication exists because the producer of the signal normally gets some benefit from it. So we should look for precursors of human-to-human communication in behaviours that benefit the signaler'' (168), and such ''communicative acts are made of the same stuff as non-communicative acts'', for example a cough, ''to get attention'', but which also just clears the throat. Such speech is pure 'act', lacking truth value: _hello_ 'greeting', _bye_ 'leave taking', _hey_ 'attention getting', etc. Interestingly, some of these English words may lack vowels (_hmm_ 'doubt'), and have clicks (_tsk tsk_) (171). Hurford supposes that ''the first communicative acts between remote ancestors of modern humans were of such purely illocutionary variety'' (175), although these are of marginal importance in languages today.
''Signals that are distinctive of social subgroups within a breeding species must be passed on through learning... chimpanzees may actively modify pant hoots to be different from their neighbors'' (181). A 'signature call' expressing 'Here I am' might be learned, or just have individual characteristics, like human laughter, but ''it is probable that uniquely complex human language could not have evolved without the social ritualized doing-things-to-each-other scaffolding found in many other social species, including our nearest relatives, the primates'' (185). Of 42 species surveyed, that ''with both the largest typical group size (125) and the largest vocal repertoire (38 calls) was the bonobos'' (188).
The ''gestural repertoire and communicative dynamics'' of rhesus and pigtail macaques ''are generally consistent with the characteristics of their social organization''; the rhesus are ''despotic and nepotistic'', lacking ''complex patterns of affiliative communication and bonding'', whereas pigtail macaques have ''intense affiliation and bonding patterns'' which ''appear to have coevolved with complex dynamics of intragroup cooperation and with considerable social tolerance'' (190). When rhesus and stumptail macaques share living space in captivity, the rhesus acquire the ''reconciliation behaviour'' of the stumptails (190, footnote). ''In their sexual arrangements, humans most closely resemble bonobos... The fluidity of bonobo society means that there is a relatively high amount of interpersonal communication, including a lot of communication around sex acts'' (194).
Mating pattern, however, may be inherited: ''Alteration of a single gene transforms a vole of a naturally promiscuous species into a monogamously inclined vole'' (192). Required are ''conditions that seem most likely to have given rise to the group-wide reciprocal social purposes for which humans use language...: large group size, relatively egalitarian individualistic social structure, and a long period of infant or child dependency'' (197), the latter providing opportunity for learning.
''The instinct to imitate is shared by humans and chimpanzees, but humans have developed it further. It is also evident that latent imitative dispositions in chimpanzees are drawn out more readily in captivity than in the wild'' (201). ''Chimpanzees who had discovered their own method of solving a practical problem'' subsequently followed the method of their companions. ''Chimpanzees, sensibly enough, can't see as much point as children in pure imitation for its own sake, with no immediate reward... The energy used in imitation by [human] infants is a kind of long-term investment, or, in an alternative metaphor, the price of an entry ticket into a game played with arbitrary symbols'' (203).
Chapter 7, ''Going Triadic: Precursors of Reference'', examines gaze-following as first evidence of the empathy which makes communication possible, and pointing as the first evidence of a 'triadic' sign, which involves something other than sender and receiver. It seems that all great apes follow the gaze of others (205). Pointing, however, while ''commonplace in captive chimpanzees'' is ''virtually absent in wild chimpanzees'' (212), suggesting readiness for, if not the practice of, referential expression. Hurford supposes the difference in captivity is owed to their being out of the food-and-sex-competitive environment of the wild; ''as they register in the wild who is dominant and who is subordinate, they register in captivity which humans are considerate towards them and which are not, and adjust their behaviour accordingly'', for example using requests, as in 96% of Kanzi's signings (217). Dogs are well up on chimpanzees in this regard, being ''more skillful than great apes at a number of tasks in which they must read human communicative signals indicating the location of hidden food'' (218). In humans, ''a link between pointing and speech development appears evident... [T]he age of onset of pointing and its frequency at 12 months predicts the amount of speech in production at 15 months and also at 24 months'' (220-1).
Hurford discusses game-theoretic evidence that evolution of human(istic) communication presupposes a degree of altruism, presence of which enables ''home-reared apes to act somewhat cooperatively with their human keepers, in this environment where cooperation [vs. competition] is the norm'' (223).
The growl of a leopard heard 5 minutes after the leopard call of the Diana monkey produces a lesser response in members of the species than such growl heard after an eagle alarm; that is, the alarm call produces not just a momentary instinctive response, but is held in memory (227). There is evidence of learning: with maturity, vervets get better both at sending and receiving alarm calls; as youngsters, they overgive the alarm, for non-predators e.g. warthogs, and their response to the calls is ''more generalized''. They give the calls less often when alone, but presence of conspecifics could be ''part of the complex of stimuli to which an innate automatic alarm-calling mechanism responds'' (230-1).
Hurford describes the research of Boysen et al (1996), suggestive of the significance for language of the symbolicness (arbitrariness) of signs. Chimpanzees were ''successfully trained in the meanings of the symbols 1-6, so they knew that 2 signifies a smaller number than 6'' then ''were trained...to perform a counterintuitive task in which selection of a lower-valued of a presented pair of symbols resulted in being given a food reward proportional to the higher-valued symbol'': presented with '2' and '6', choose '2' and receive 6 pieces of food. They learned to choose the lower-valued numeral to receive the greater amount of food. If, instead, different numbers of pieces of food are presented, they fail utterly (238). As Hurford says (240), ''humans have evolved an ability to detach their overt physical responses to signals from direct action responding to the referents of the signals'', which recalls the more vivid words of Huxley (1977: 172): ''Human beings...thanks to language, are able to pursue one purpose or to act in relation to a principle or to an ideal over long periods of time. In a certain sense we can say that language is a device for permitting human beings to go on doing in cold blood the good and the evil which it is possible for animals to do only in hot blood, under the influence of passion.''
Hurford suggests that planning may have been selective, by ''a co-evolutionary feedback cycle between an enhancement of ability to plan for predator-avoidance and food-getting and a decrease in the immediacy of survival pressures'' (240); ''the quantitative dispositional differences (admittedly great) between humans and apes... can be accounted for by gradual change under pressure from social arrangements conducive to free exchange of information'' (242).
Ch. 8, ''Why Communicate? Squaring with Evolutionary Theory'', develops arguments for the social environment needed for language to arise. This is in addition to two cognitive needs already identified and thought satisfied in animals, if undeveloped: 'symbolic vocabulary' and 'deictic/symbolic integration' (using the vocabulary referentially, probably at first with pointing). The cognitive needs depend on the social, because they ''can only take off if the animals concerned are disposed to give each other information'' (242).
Grice's 1967 Principle of Cooperation and Sperber and Wilson's 1986 Relevance Theory contain the gist of what must have been needed, a sort of mind reading; and ''...figuring out the intentions of others is not a uniquely human attribute'' (253). A chimpanzee, for example, seeing another make a move towards food accelerates its own movement, and may copulate behind a rock to avoid being seen by a dominant male.
However, 86% of banana giving among wild chimpanzees was between mother and offspring (256), so the necessary altruism has to start among kin. In human murders, in fact, ''unrelated cohabitants are at dramatically higher risk than related cohabitants'', and ''universal kinship systems'', in which all members of a social group are or are thought to be kin, ''are widespread, especially among hunter-gatherers'' (262). Species that don't show a lot of cooperative behavior can acquire it: blue jays ''figured out very quickly what was to their own individual advantage'': to cooperate in key pressing, which yielded more food for both (273).
Sexual selection of communication (attracting better mates), as apparently in birdsong, doesn't seem relevant in the human context, where we acquire language as children, ''before...traits associated with sexual attraction come onstream'', though male voice lowering at puberty may argue otherwise (284); nor does recursion at all appear to be sexually selective (285), although it might once have been. While DNA is the 'replicator' in natural selection, the individual is its 'vehicle', and ''the social group is the survival vehicle of its individual members'' (295). Cooperative communication including altruism is reasonably a selective trait of social groups.
Altruism can evolve in ''groups of individuals living close and sharing observable traits identifying them as appropriate recipients of altruism'', e.g. dialect, a ''badge of group membership'', which can explain why dialects are acquired early to the (near) exclusion of late: to keep out imposters (301), which ''gets us close to a scenario of the co-evolution of cooperative/altruistic communication with the learned communicative code itself as a group identity tag.'' And to distance one group from another: thus the ''many different manifestations of language'' (302).
Chapter 9, ''Cooperation, Fair Play, and Trust in Primates'', ''examine[s] the extent to which behaviour reflecting any kind of social contract exists among primates'' (307), because ''a cohesive social group...could be a unit of selection'' (306). Hurford believes an ape has a rudimentary ''theory of mind'', having some notion that ''other creatures (usually conspecifics) go through the same mental processes as it does'' (307). In one experiment, a subordinate chimpanzee could see which one of two pieces of food a dominant chimpanzee could see. Released into the cage, it ''chose to go'' to that which the dominant could not see. ''Chimpanzees are better than capuchin monkeys'' in this circumstance (311). Zoo workers readily rate their chimpanzee charges in helpfulness (cooperativeness), among other personality characteristics, and Hurford says such ''variability, of course, is the fuel of natural selection'' (313).
Hurford quotes Tomasello et al (2005) that ''it is almost unimaginable that two chimpanzees might spontaneously do something as simple as carry something together''; they lack ''shared intentionality'' (316). Group hunting by e.g. wolves and chimpanzees doesn't count; each animal just does its thing, with full context boundedness. Hurford wonders if ''a system of learned arbitrary symbols, such as humans use, [could] evolve in a community where the individuals were not disposed to participate in shared tasks, having tacitly divined the intentions of others'' (320).
Macaques, in fact, punish others who keep their food finds to themselves, and chimpanzees ''from a more stable and long-lasting social group were more tolerant of others receiving better rewards'' (323). Interesting new evidence concerns oxytocin, ''a neuro-peptide that plays a key role in social attachment and affiliation in non-human mammals''. Even in an investment game played by humans, intranasal administration of oxytocin ''causes a substantial increase'' in trusting behavior (327).
Chapter 10, ''Epilogue and Prologue'', expresses the conclusion that, in the wild, apes have ''quite a lot going on in their heads'', indeed ''rich mental lives''. Captivity and cooperative lives with humans brings out latent possibilities (333), all of which Hurford considers significantly explanatory of possibility for the appearance of language in humans, though of course mysteries remain, including ''why humans and not others.'' Volume 2 will concern ''the cascade of consequences'' which, ''as soon as the breakthrough was made for animals to communicate their thoughts relatively freely to others,... were selected, designed to make the transfer of information more effective, and allowing humans to enrich their mental representations by thinking about the representations themselves'' (333).
EVALUATION All this is admirably persuasive and thought provoking, and puzzling largely to the extent that it raises questions the answers to which may be hoped for in the forthcoming Volume 2. Perhaps in the present volume something of worth might have been said, at least anticipatorily, about the societal structures and cooperative activities of present-day and hypothetical early-human hunter-gatherer societies. Particularly the pre-agricultural knowledge of plants, in the discovering and preserving of facts about their use, seasonality, and location, all critical cultural knowledge, must have been a strong impetus to the use of propositional language.
Also, the apparent division of the two volumes into origin of meaning and origin of form perhaps separates actually inseparable meaning and form aspects of the sign, as insisted by Saussure and often since thought essential to the nature of the sign. Perhaps volume 2 on origin of form is going to connect or unify these, or show how one aspect or the other is original, or how the two coevolved but somehow independently.
Finally, some might question Hurford's utter commitment to mentalism, ''that the relationship of meaning between language and the world is indirect, and is mediated by the mind, which is host to such things as concepts, ideas and thoughts'' (5). Hurford argues that animals have minds (51, 308-9); but never questions the extent to which these must be attributed to humans.
In addition to these general remarks, I have two specific ones. First, Hurford describes pointing as ''largely'' indexical, with the qualification owed to ''the difficulty of imposing Peirce (1897/1955)'s trichotomy icon/index/symbol in a completely watertight way'' (225). In fact, Peirce's definition may be sufficient that pointing is exactly indexical: ''a sign which refers to the Object that it denotes by virtue of being really affected by that Object''. Non-rhetorical pointing is useless unless the object is REALLY pointed to. ''Deictic words such as _this_ and _here_ are, besides being indexical, also symbolic, having only arbitrary relationship to their meanings, and needing to be learned in each separate language'' (225). 'Indexical' here seems to mean 'demonstrative, pointing' - not the Peircean sense. _This_ and _here_, by the way, while entirely symbolic in usage (Peirce: ''denotes by virtue of a law''), have long been noted to have a seeming indexical aspect, perhaps from their origin, having in many languages high (in-pointing) vowels vs. low (away-pointing) vowels of their opposites (_that_, _there_); examples are many, e.g. Amharic [yih] 'this', [izzih] 'here' ([ya] 'that', [izzya] 'there'). The probable iconic/indexical raw origin of words was argued in Plato's Cratylus: ''That objects should be imitated in letters and syllables, and so find expression, may appear ridiculous,...but it cannot be avoided - There is no better principle to which we can look for the truth of first names. Deprived of this, we must have recourse to divine help, like the tragic poets'' (Salus 1969: 58). This may be important in the evolutionary appearance of language, for it means that we have no need to insist therein on the symbolicness of signs, as perhaps does Hurford (236). Arbitrariness will arise within few generations of imperfect imitation, or 'emulation' in Hurford's term (199). Even non-concrete meanings could originally have indexical aspects, and it seems reasonable that the vervet's leopard (bark), eagle (cough), and snake (chutter) calls would also have started out indexical.
Second, on at least one occasion, Hurford's interpretation of the evidence falls short of fully satisfactory. For example, bonobo chimpanzees and orangutans are said to stash tools needed for searches as much as 14 hours later, so ''some kind of representation of where the animal wants to be in the immediate future seems to be involved'' (77). But such result needs to be compared with that in which use of the tools was not expected; otherwise they are just associating the tools with food and acting accordingly. Also, evident surprise by a babboon on hearing a ''recording of a dominant babboon making a submissive noise'' is said (81) to ''demonstrate knowledge of a social fact, who-dominates-whom'', which needs to be contrasted with surprise at other simply odd events.
I noted only 11 typographical or form errors, none of which might confound a reader. Hurford's preference for writing e.g. ''Frege (1879)'s'' vs. ''Frege's (1879)'' is obviously deliberate if questionable.
REFERENCES Boysen, S. T., G. G. Berntson, M. B. Hannan, and J. T. Cacioppo. 1996. Quantity-based interference and symbolic representations in chimpanzees (Pan troglodytes). _Journal of Experimental Psychology: Animal Behavior Processes_ 22.1: 76-86.
Chomsky, Noam. 2006. _Language and Mind_, 3rd. ed. Cambridge: Cambridge University Press.
Dennett, Daniel. 1991. _Consciousness Explained_. Boston: Little, Brown.
Dobzhansky, Theodosius. 1973. _Nothing in biology makes sense except in the light of evolution_. The American Biology Teacher 35: 125-129.
Heine, Bernd and Tania Kuteva. 2007. _The Genesis of Grammar_. Oxford: Oxford University Press.
Huxley, Aldous. 1977. _The Human Situation: Lectures at Santa Barbara, 1959_. New York: Harper & Row.
Miller, George A. 1956. The magical number 7 plus or minus 2. _Psychological Review_ 63: 81-97.
Peirce, Charles S. 1955 [1897]. Logic as semiotic: the theory of signs. In _Philosophical Writings of Peirce_, Justus Buchler, ed., 98-119. New York: Dover.
Pinker, Steven. 2003. Language as an adaptation to the cognitive niche. In _Language Evolution_, Morton H. Christiansen and Simon Kirby, eds., 16-37. New York: Oxford University Press.
Salus, Peter, ed. 1969. _On Language: Plato to von Humboldt_. New York: Holt, Rinehart and Winston.
Tomasello, M. M. Carpenter, J. Call, T. Behne, and H. Moll. 2005. Understanding and sharing intentions: the origins of cultural cognition. _Behavioral and Brain Sciences_ 28: 675-735.
ABOUT THE REVIEWER Grover Hudson has taught phonology, historical linguistics, and Ethiopian linguistics incuding Amharic language at Michigan State University. He is author of a comparative historical dictionary of Highland East Cushitic languages, an introductory linguistics textbook, with Anbessa Teferra a recent book on Amharic, and numerous articles on phonology and Ethiopian linguistics, including recently on archaic traits in Ethiopian Semitic languages.
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