We agree that language adapts to the brain, but we note that language also has to adapt to brain-external constraints, such as those arising from properties of the cultural transmission medium. The hypothesis that Christiansen &amp; Chater (C&amp;C) raise in the target article not only has profound consequences for our understanding of language, but also for our understanding of the biological evolution of the language faculty

Ackley

Andrew D. M. Smith

Kenny Smith

Kirby

Simon Kirby

Smith, Kenny

Kirby, Simon

Smith, Andrew D M

Stirling Online Research Repository

on L1 acquisition, I argue that the authors’ elegant conceptualiz-ation and simulations of the logical problem of language evol-ution do not necessarily translate to the untidy developmentalfacts of language acquisition in the current linguistic environ-ment. Specifically, it may be premature on C&C’s part to advo-cate general-purpose cognitive mechanisms alone to explainchild language learning and the repertoire of rule types thatgoverns it.As a first step, terms such as “language-specific constraints”and “general-cognitive constraints” must be regarded withcaution. While domain specificity is often readily identified,domain generality is frequently a “moving target,” preciselybecause it is definable by degree. That is, we say that a mechan-ism is domain-specific so long as it only does what it evolved todo, or as long as it is only used for learning within its domain.But we can only say that a mechanism is more or less domain-general: It is more domain-general or neutral the more it gener-alizes to other tasks outside its domain. In principle, this effectmay not be problematic – after all, lots of phylogenic and onto-genic distinctions involve matters of degree. In synchronicterms, any general mechanisms of cognition do not dispensewith the specific ones; instead, the existence of general machin-ery presupposes the existence of functionally related specificmechanisms. When dealing with the countless complexities oflinguistic structure, Skinner’s box cannot afford to be empty: itmust at least contain a random assortment of various entities(paraphrasing Satterfield & Saleemi 2003). In other words, thebasis from which L1 development commences had better beminimally equipped to supply learners with knowledge of gram-matical functions, and Case systems, and so on, just in case chil-dren encounter these properties in their primary linguistic data.Second, C&C state thatif language is viewed as having been shaped by the brain, thenlanguage learning is by no means a standard problem of induc-tion . . . instead, the task is simply to give the same answer aseverybody else – because the structure of language will haveadapted to conform to this most “popular” guess. (sect. 8.1,para. 2)This view has several consequences in the developmental contextthat are not easy to explain. Consider the following cases: (1)Children in American English-speaking environments arewidely attested to omit subject pronouns in tensed clauses(e.g., Toys in there; Hyams 1986). (2) They also insert an extrawh-expression in long-distance questions: for example, “Whatdo you think what pigs eat?” (Crain & Thorton 1998). The struc-tures in question seem to be at odds with “everybody else” – forexample, with adult English, which contains no such features(although these are by no means “wild guesses,” since in theformer case [1], languages like Standard Spanish and Italianpattern somewhat in this way; and in the latter case [2], certainGerman dialects would be appropriate). However, it would becomputationally “easier” to simply have a zero or deleted Com-plementizer in this site, rather than the wh-word. These tokensbeg the question of why children should exhibit such tendenciesat all. Perhaps the task requires children to initially exert multipletypes of “biases” in order to obtain the maximal advantages of thegrammar (Gawlitzek-Maiwald & Tracy 2005; Roeper 1999;Saleemi 2002; Satterfield 1999a; 1999b; Yang 1999; 2002).On common ground with C&C, it is doubtful that a highlylanguage (domain)-specific Universal Grammar (UG) functionsas the sole machinery in the child’s task of language acquisition.However, this position need not exclude the possibility that child-ren pick which apparatuses they use, more-generalized or less-generalized tools, and to what degree, in a flexible and adaptivemanner. Keeping this postulation in mind, consider the criticalperiod in L1 acquisition. It has been successfully argued thatnot all aspects of language display critical period effects. Specifi-cally, the acquisition of lexical items, the concatenation of words,and the nuts and bolts of semantically based principles of wordorder seem immune to age-related “atrophy” of language acqui-sition (Hudson & Newport 1999; Jackendoff 2002; Sorace 2003).However, the capacity to acquire other parts of language inlate language learning, such as the inflectional system or realintricacies in phrase structure, appears to be largely dimini-shed (Lardiere 1998; 2000). These common L1 versus L2conditions become at once isolatable by viewing language acqui-sition as a multi-layered construction with distinct learningmechanisms.Ultimately, the solution to the logical problem of languageacquisition may reside in the possibility of possessing severalinitial knowledge states in which domain-general mechanismsinteract with domain-specific components designed to acquirethe most arbitrary and least systematic knowledge of the targetgrammar. States that stabilize over several progressive stagescould then emerge, with the help of additional domain-generallearning mechanisms, which handle increasingly more systema-tic principles of the grammar. In sum, each transitional statemay be shaped by the myriad effects of learning, or, more appro-priately, of acquisition, which can be viewed as the combina-tion of experience and internally determined processes suchas maturation, learning mechanisms, and language-specificcomputations.The brain plus the cultural transmissionmechanism determine the nature of languagedoi:10.1017/S0140525X08005244Kenny Smitha, Simon Kirbyb, and Andrew D. M. SmithbaCognition and Communication Research Centre, Division of Psychology,Northumbria University, Newcastle-upon-Tyne, NE1 8ST, United Kingdom;bLanguage Evolution and Computation Research Unit, School of Philosophy,Psychology and Language Sciences, University of Edinburgh, Edinburgh,EH8 9LL, United Kingdom.kenny.smith@northumbria.ac.ukhttp://drkennysmith.googlepages.com/simon@ling.ed.ac.ukhttp://www.lel.ed.ac.uk/~simon/andrew@ling.ed.ac.ukhttp://www.lel.ed.ac.uk/~andrew/Abstract: We agree that language adapts to the brain, but we note thatlanguage also has to adapt to brain-external constraints, such as thosearising from properties of the cultural transmission medium. Thehypothesis that Christiansen & Chater (C&C) raise in the target articlenot only has profound consequences for our understanding oflanguage, but also for our understanding of the biological evolution ofthe language faculty.Christiansen & Chater (C&C) provide a thought-provokingaccount of language as a cultural adaptation to the minds oflanguage learners: Language evolves through repeated culturaltransmission, adapting to multiple pressures impinging upon itslearning, representation, and use. This strikes us as a powerfulexplanatory framework, and we hope the target article will stimu-late more work fleshing out the precise relationship between con-straints on language arising from the brain and features oflinguistic structure.In fact, we believe that there are two respects in which thetarget article actually understates the full implications of thishypothesis. First, C&C focus on language as an adaptation tolanguage learners’ brains – but language must also adapt to con-straints external to the human mind. Second, in discussing theiraccount’s implications for understanding biological evolution,C&C point out the “moving target” problem – but there are atleast two further issues with the interaction of cultural and bio-logical evolution they do not recognize. Taken together, thesecompletely change the viability of accounts based on the adaptiveCommentary/Christiansen & Chater: Language as shaped by the brainBEHAVIORAL AND BRAIN SCIENCES (2008) 31:5 533evolution of a strongly constraining, domain-specific biologicalfaculty for language.Although there are, of course, fundamental differencesbetween the account offered by C&C and the UniversalGrammar (UG) account they contrast it with, it is useful never-theless to focus on a point of similarity: Both argue that languageis how it is because the mind forces it to be so (the crucial differ-ence being the extent to which the relevant mental componentsare domain-specific or domain-general, and who does the fittingto what). Both postulate a good fit between observed propertiesof language and properties of the human mind: if we see somelinguistic property in the world, we can reasonably infer that itreflects a property of our minds.We have previously demonstrated, however (Kirby 1999;Kirby et al. 2004), that mental properties cannot simply beread off from language universals, because the cultural processmediating between aspects of the mind and features of languagedistorts the underlying biases of human learners. For example,culture can amplify weak biases to give strong universal effects.This means that cultural transmission can obscure underlyingdifferences in mental structure: for example, strong universaltendencies towards regularity can result from various levels ofpreference for regularity in individual learners, and (in extremecases) the same observed distribution of languages can resultfrom learners with widely differing strengths of preference forregularity (Kirby et al. 2007).This suggests that, while we can probably get an idea of thegeneral flavour of the human mind from observable linguisticproperties, making specific inferences is more risky. To drawappropriate conclusions from a given distribution of languages,we must understand the rather opaque relationship betweenmental properties and linguistic properties resulting from cul-tural transmission.Furthermore, not all pressures acting on language during itstransmission are mental: language is not only well adapted toits users’ brains, but also to its medium of transmission. Compu-tational modelling work highlights the importance of the learningbottleneck: learners must infer the structure of an infinitely largelanguage from a finite subset. This bottleneck introduces apressure for generalisation to which language must adapt, forexample, by becoming compositional (Kirby 2001; Smith et al.2003a). Importantly, the bottleneck is not a property of languagelearners’ brains, but rather of the medium through whichlanguage is transmitted, namely, a finite dataset. Linguistic prop-erties that are eminently learnable (and therefore well adapted tothe brain) may be disfavoured due to this transmission factor, orvice versa. Consequently, linguistic features represent a productof, or a compromise between, several pressures acting onlanguage transmission, some (but not all) of which reside in thehuman brain.There are therefore good practical reasons for taking culturalevolution seriously. However, cultural evolution is more thanjust a methodological hassle for cognitive scientists: the samearguments radically alter the plausibility of scenarios for the evol-ution of the language faculty. C&C point out one problem forbiological evolution, which arises from cultural transmission –evolution is chasing a moving target. We raise an additionalproblem: Given the opaque relationship between mental andlinguistic features, much of the human biological capacity forlanguage will be shielded (Ackley & Littman 1992) from evol-ution. For example, Kirby et al. (2007) show that the strengthof prior preferences for particular structures in languagearising from an individual’s biology may have no effect on thestrength of the resulting universals. Under this scenario, selectionis completely blind to the strength of the prior biases of indivi-duals and there is no selection for nativisation, nor for stronger,“more desirable” prior preferences for certain languages(Smith & Kirby 2008).Furthermore, cultural transmission may actually hinder theevolution of a priori functional domain-specific features of thelanguage faculty: Evolving biases for communicatively functionallanguages is problematic for culturally transmitted languages,because the biases of individual learners require a critical massof learners and a reasonable span of cultural time to make theiradvantageous properties felt (Smith 2004). Indeed, based onsuch models, we expect that practically the only scenario underwhich biological evolution will favour particular language-learn-ing predispositions is when those predispositions are domain-general, and selected for on account of their less problematic(acultural, non-linguistic) applications. While this is entirely con-sistent with C&C’s argument, we believe it also follows naturallyfrom taking cultural evolution seriously.So if evolving a functional domain-specific set of languagebiases is problematic, how can we best understand the evolutionof the human faculty for language? C&C force us to revisitthe human uniqueness of language from a comparative pers-pective, and (we suggest) pose a fascinating, important newchallenge for evolutionary biology: Which of their suggesteddomain-general pressures responsible for shaping languageare unique to humans, and what can this tell us about the evol-utionary origins of the species-unique trait of language? Arethere pre-adaptations for the cultural transmission of linguisticsystems (e.g., vocal learning capacity; intention-sharing ability)?If so, how much linguistic structure naturally falls out of thecultural transmission process once these pre-adaptations arein place?Case-marking systems evolve to be easyto learn and processdoi:10.1017/S0140525X08005256Maggie TallermanCentre for Research in Linguistics and Language Sciences (CRiLLS),Newcastle University, Newcastle upon Tyne, NE1 7RU, United Kingdom.maggie.tallerman@ncl.ac.ukhttp://www.ncl.ac.uk/elll/staff/profile/maggie.tallermanAbstract: Christiansen & Chater (C&C) suggest that language is itself anevolutionary system, and that natural languages “evolve” to be easy tolearn and process. The tight economy of the world’s case-markingsystems lends support to this hypothesis. Only two major case systemsoccur, cross-linguistically, and noun phrases are seldom overtly case-marked wherever zero-marking would be functionally practical.All languages employ some morphosyntactic means of dis-tinguishing the core noun phrase (NP) arguments within aclause. The two basic predicate types are intransitive and transi-tive verbs, giving three core grammatical functions: S indicatesintransitive subjects (The girl slept); A, “agent” of a transitiveverb (The girl saw a pig); and P, “patient” (The girl saw a pig).Some languages (e.g., Chinese, English) distinguish A and Pusing word order: thus, we know which mammal saw which,because A always precedes the verb and P follows.However, many languages employ case-marking to distinguishA and P, as in Latin:1a. Puella venit.girl.(NOM) come.PRES.3SG“The girl comes.”1b. Puella puer-um audit.girl.(NOM) boy-ACC hears.PRES.3SG“The girl hears the boy.”1c. Puella-m puer audit.girl-ACC boy.(NOM) hear.PRES.3SG“The boy hears the girl.”Commentary/Christiansen & Chater: Language as shaped by the brain534 BEHAVIORAL AND BRAIN SCIENCES (2008) 31:5

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The brain plus the cultural transmission mechanism determine the nature of language

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We agree that language adapts to the brain, but we note that language also has to adapt to brain-external constraints, such as those arising from properties of the cultural transmission medium. The hypothesis that Christiansen &amp; Chater (C&amp;C) raise in the target article not only has profound consequences for our understanding of language, but also for our understanding of the biological evolution of the language faculty.</p

Smith, Andrew D. M.

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The brain plus the cultural transmission mechanism determine the nature of language

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