Language and life history: A new perspective on the development ...

Commentary/Locke & Bogin: <strong>Language</strong> <strong>and</strong> <strong>life</strong> <strong>history</strong>1990). Pidgins are protolanguages used by people from differentlinguistic backgrounds who are brought together to live <strong>and</strong>work, whereas creoles are true languages. More convincing yetof children’s collective ability to invent language comes from ageneration of deaf Nicaraguans who had not been exposed to adeveloped language <strong>and</strong> who, prior to attending a <strong>new</strong> schoolfor the deaf, communicated using idiosyncratic home-signsystems. Shortly after arriving at the school, these home signersdeveloped a shared system of signs <strong>and</strong> grammatical devices.This shared system developed into a full-fledged sign languageafter several years <strong>and</strong> several cohorts of typically young, deafindividuals without the need for instructions or adult models(Senghas & Coppola 2001; Senghas et al. 2004).The emergence of <strong>new</strong> skills, such as language or its antecedents,in a group of individuals can place them in novel contexts<strong>and</strong> expose them to <strong>new</strong> selection pressures. This would surelyhave been the case with the emergence of language <strong>and</strong> itsunderlying symbolic abilities. We argue, as have others (e.g.,Gottlieb 2002; Lickliter & Schneider, in press; West-Eberhard2003), that the neural plasticity of infants <strong>and</strong> children <strong>and</strong>their behavioral <strong>and</strong> cognitive responses to novel environmentsprovide much of the stuff upon which natural selection works,<strong>and</strong> that this may have been especially important in recenthuman cognitive evolution (e.g., Bjorklund 2006). Such plasticitymay continue to afford the opportunity for phylogeneticchange in Homo sapiens. For instance, the Flynn effect, asteady rise in IQ (particularly fluid intelligence) over the pastcentury, may be due to accelerated cognitive development(Howard 2001), perhaps in response to an increasingly visualenvironment (see Neisser 1988). We do not believe that thehuman race is on the verge of a radical evolutionary change;but the neural plasticity evident in contemporary childrenin response to changing environments likely also characterizedour ancestors <strong>and</strong> contributed centrally to the emergenceof language <strong>and</strong> related sociocognitive abilities in ourforechildren.Reconciling vague <strong>and</strong> formal models oflanguage evolutionHenry Brighton, Rui Mata, <strong>and</strong> Andreas WilkeCenter for Adaptive Behavior <strong>and</strong> Cognition, Max Planck Institute for HumanDevelopment, 14195 Berlin, Germany.hbrighton@mpib-berlin.mpg.de http://www.ling.ed.ac.uk/henryb mata@mpib-berlin.mpg.de http://www-abc.mpibberlin.mpg.de/users/matawilke@mpib-berlin.mpg.dehttp://www-abc.mpib-berlin.mpg.de/users/wilkeAbstract: One way of dealing with the pro<strong>life</strong>ration of conjecturesthat accompany the diverse study of the evolution of language is todevelop precise <strong>and</strong> testable models which reveal otherwise latentimplications. We suggest how verbal theories of the role of individualdevelopment in language evolution can benefit from formal modeling,<strong>and</strong> vice versa.Research into the evolution of language is growing rapidly <strong>and</strong> itsstudy now cuts across several disciplines. Despite the diversesources of insight which make up this field of study, few woulddisagree that underst<strong>and</strong>ing how <strong>and</strong> why our species-specificlinguistic communication system came to be, requires a considerationof the interactions among three processes: biological evolution,linguistic evolution, <strong>and</strong> individual development (e.g.,Christiansen & Kirby 2003b). Consequently, we were pleasedto see Locke & Bogin’s (L&B’s) target article focus on oneoften-neglected component – individual development – <strong>and</strong> itsrelation to biological evolution. However, in order to underst<strong>and</strong>the implications of a theory of individual development <strong>and</strong> itsrelationship to the evolution of language, we must go beyondvague models whose implications are hard to gauge <strong>and</strong> movetowards more formal <strong>and</strong> testable models.Dominating the study of language evolution is the desire tounderst<strong>and</strong> the unique form of structural complexity we see inhuman language. In other words, we seek an explanation ofhow certain forms of complexity arise from an initial statewhere that complexity was lacking. As L&B discuss, language isa communication system used in many interesting <strong>and</strong> uniqueways. However, it is misleading to assume that by studying thecommunicative uses to which language is put we can gaininsight into why language is so structurally distinct from othercommunication systems. L&B emphasize that language is usedto support functions which contribute to an individuals’ reproductivesuccess. However, the degree to which the specific structureof language is required for such functioning is by no meansclear. First, although most organisms communicate, <strong>and</strong> thosethat do so effectively are likely to be at an advantage over thosethat do not, only one species has language. Second, one canimagine many c<strong>and</strong>idate communication systems that fulfillsuch requirements. Furthermore, language arguably does afairly bad job as a communication system (e.g., Chomsky et al.2002). In sum, the evolution of language cannot be explainedby its communicative function alone.To fully underst<strong>and</strong> language <strong>and</strong> its emergence we have tounderst<strong>and</strong> the interacting adaptive systems that have driven itsevolution. An important tool in this endeavor is the use offormal modeling, which allows us to explore the implications ofprecise <strong>and</strong> testable hypotheses. The growing interest in theevolution of language has been accompanied (some might sayspurred) by an upturn in mathematical <strong>and</strong> computationalmodels (e.g., Briscoe 2002; Cangelosi & Parisi 2001; Hurford1989; 2005; Kirby 2002; Nowak & Komarova 2001).We would like to highlight how formal approaches to studyingthe evolution of language can profit from further consideration ofthe process of individual development. First, development is acrucial step in determining the class of acquirable communicationsystems. The ontogenetic development of the cognitivemachinery responsible for processing languages may be tied tostages in the <strong>life</strong> course, <strong>and</strong> this developmental path is likelyto be crucial to underst<strong>and</strong>ing the structural characteristics oflanguage. For example, computational modeling of languageacquisition has shown the importance of considering howlanguage structure relates to cognitive systems <strong>and</strong> their development.Elman (1993) used neural network simulations to showhow networks can learn certain forms of linguistic structure ifmemory is started small <strong>and</strong> then gradually exp<strong>and</strong>ed. Thismirrors the development of short-term memory capacity inhumans <strong>and</strong> suggests that the mind may be tuned to develop inparticular ways to facilitate learning. Elman’s work demonstrateshow the maturational trajectory over an agent’s <strong>life</strong>time canimpact on what is <strong>and</strong> what is not ultimately acquirable. Furthermore,the particular form of inductive bias that defines thelanguage learner has a knock-on effect when we considerwhich kinds of structure can withst<strong>and</strong> repeated culturaltransmission (Brighton et al. 2005b; Smith 2004).Second, individual development is characterized not only bychanges in cognitive aspects but also in social aspects, such asthe structure of social networks. The social networks in which adeveloping individual is situated impacts on how language istransmitted between generations (e.g., Kerswill & Williams2000; Ragir 2002). If constraints on how language is transmittedfrom one generation to the next impact significantly onthe distribution of linguistic forms (e.g., statistical universals;for a discussion see Brighton et al. 2005a), then the socialnetworks through which language is transmitted are likely toplay a significant role (Smith & Hurford 2003). Hence, theimplications of changing social networks that L&B discusscould be explored by investigating how they impact, over acultural timescale, on the distribution of language’s structuralcharacteristics.282 BEHAVIORAL AND BRAIN SCIENCES (2006) 29:3