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

Response/Locke & Bogin: <strong>Language</strong> <strong>and</strong> <strong>life</strong> <strong>history</strong>wolves, birds, squirrels, frogs, apes, monkeys, <strong>and</strong> othernonlinguistic species that are addressed in The Evolutionof Communication. What, then, is language? Chomskyresponds that it is “a system for expressing thought”(Chomsky 2002a, p. 76). This, he says, makes language“quite different” from the signaling systems of animals.Fair enough, but the expression of thought is whatpeople have in mind when they say that language isused to communicate. It is virtually the dictionarydefinition.In the target article, we discussed Hauser et al.’s (2002)distinction between broad <strong>and</strong> narrow conceptions of thefaculty of language. Bickerton suggests that we misinterpretthis distinction “as licensing the subsuming ofstructural <strong>and</strong> pragmatic elements under a singleumbrella” while evincing no awareness of the argumentsthat we actually made for the “single umbrella.” In thetarget article, we sampled evidence from development,evolution, <strong>and</strong> genetics. The messages from these fieldsconverge upon a single conclusion: the capacity forspeech is intimately related to other levels of language.Developmentally, it is evident that infants who have difficultywith word learning are likely to have problems lateron with grammar or pragmatics, even if their lexicaldifficulties abate. Evolutionarily, it is evident, on logicalgrounds, that grammar <strong>and</strong> other areas of language mustbe related. For if some observable behavior increasedfitness at sexual maturity, then developmental precursorswould have been incidentally reinforced – developmentbeing continuous – by virtue of facilitative relationshipsof the sort that have been documented in contemporaryhumans. In behavioral <strong>and</strong> molecular genetics, analysesof individuals with problems at multiple levels of languagehave revealed stronger or more consistent effects inthe areas of phonetics <strong>and</strong> phonology, effects that implya vocal influence in the development of all areas oflanguage.The commentary by Bickerton was not the only one toraise connections between language <strong>and</strong> thought. Oneother, that of Van Herwegen & Karmiloff-Smith,points out that we do not say whether it is language thatmakes humans intelligent. These commentators claimthat the uniqueness of humans depends on the ability“to re-represent their representations into an explicitformat, transportable from one domain of knowledge toanother one.” This may be true, but it has nothing to dowith our stated objective, or with any claims that wehave made.Johansson et al. suggest that by failing to deal with “patternedcontent” (something that also concerned Brightonet al., Gogate, <strong>and</strong> Powers) we do not actually explainlanguage. What we did do was identify <strong>life</strong> <strong>history</strong>changes that would have provided critical opportunitiesfor increased plasticity, flexibility, <strong>and</strong> innovation of relevantbehaviors. We also presented arguments for thereproductive advantages of vocal, articulate, <strong>and</strong> referentialbehaviors during different stages of <strong>life</strong> <strong>history</strong>, frominfancy to adolescence. We made no attempt to explaingrammar, though a <strong>life</strong> <strong>history</strong> approach such as ourscould well converge, at some point, with ongoing work onphonetic <strong>and</strong> phonological patterns (Locke 2000a;MacNeilage & Davis 2000; Ohala 2005; Studdert-Kennedy1998; 2005). It could also produce an account of vocalcomplexity that interfaces with syntax (see sect. R5).R3. Developmental contributions to the evolutionof languageIt was gratifying to receive comments on the role of developmentin evolution by several scholars who have inspiredour own thoughts in this area. Gardner congratulates usfor adopting a biological framework, <strong>and</strong> for achieving anaccount that is more credible <strong>and</strong> relevant than strictly linguisticformulations. Bjorklund & Grotuss commend usfor focusing on the role of childhood in evolution. Our ownvaluation of the young emphasized their creativity, in thecontexts of parental care <strong>and</strong> play. These commentatorscall attention to a possible extrafamilial contribution ofthe young: play groups in which words are combined innovel ways to form <strong>new</strong> words <strong>and</strong> rudimentary syntax.They also point to the unusual plasticity of the developingbrain, suggesting that this might have endowed the youngwith a responsiveness to environmental change surpassingthat of mature individuals. We see merit in both ideas, <strong>and</strong>also in their suggestion that language, <strong>and</strong> its antecedents,may have altered the contexts in which the young foundthemselves, exposing them to novel selection pressures.One change of context may have involved increases inthe size of working groups. In hominins, the ability tospeak may have facilitated <strong>new</strong> levels of organization,enabling increases in group size. This would haveincreased cooperation in some areas, such as predatordefense, while increasing within-group competition forphysical resources (Locke 2005), though a reverse-ordereffect has been argued in which larger groups encourageda transition from manual to vocal grooming <strong>and</strong> speech(Dunbar 1993). Larger groups would also have increasedsociosexual competition, as we suggested earlier, whichmay have affected males <strong>and</strong> females, <strong>and</strong> their uses ofvocal <strong>and</strong> verbal behavior, differently (see sect. R4).When Kuiper refers to “analytic decomposition” of anenlarging “phrasal” vocabulary, he is proposing that suchan act promoted the evolution of grammatical mechanisms.We agree, having argued in the past that in development,too, grammatical mechanisms are pressured intoaction by a burgeoning store of prosodic forms. In thesecond year of <strong>life</strong>, about half of infants’ distinct utterancesmay be of this sort (Lieven et al. 1992; Locke 1997). Manypersist in prosodic form, seemingly immune to segmentaldecomposition. We have proposed elsewhere that whenthis sort of material begins to overflow its memorialbanks, typically in the third year, it triggers activation ofa system that analyses entries into elements correspondingto linguistic units (Locke 1993; 1997). This leads to moreefficient storage <strong>and</strong> permits grammatical computation.Hence, it may be said that words <strong>and</strong> phrasal words notonly precede grammar, but provide its justification.Johansson et al. say that we fail to show why chimpanzeesdid not evolve language, but that “buried” in ouraccount “is the germ that may save” us. Fortunately,they were not forced to dig too deeply to find it. Thegerms – bipedalism, pelvic narrowing, <strong>and</strong> helplessness –were key components of our argument. We, like Johanssonet al., proposed increases in proximity, attention, <strong>and</strong> careas key ingredients in the evolution of language as well as itsdevelopment (Locke 1993).King <strong>and</strong> Cowley wish we had placed more emphasison interaction. We agree with Cowley that language,which is typically manifested as speech, is more often306 BEHAVIORAL AND BRAIN SCIENCES (2006) 29:3