Wilkins & Wakefield assign importance to motor systems but skip from anatomy to cognitive structure with little attention to behavior. Organisms, no matter how sophisticated, that do not behave in accord with what they know will fall by the evolutionary wayside. Facts about behavior can supplement the authors' theory, whose hierarchical structures can accommodate an evolutionary scenario in which a million years or more of functionally varied utterances mainly limited to single words is followed by an explosion of linguistic diversity (...) with the development in the last 50,000 years or so of syntactically organized multiple word utterances. (shrink)

Preadaptation for language is an unnecessary assumption because intermediate stages of linguistic ability are possible and adaptive. Language could have evolved through gradual selection from structures exhibiting few features associated with modern structures. Without physical evidence pertaining to language ability in prehabilis hominids, it remains possible that selective pressures for language use preceded and necessitated modern neurolinguistic structures.

Despite some sound basic assumptions, Wilkins & Wakefield portray a Homo habilis too linguistically sophisticated to fit in with the subsequent fossil record and thereby lose a reasoned explanation for human innovativeness. They err, too, in accepting a single-level model of conceptual structure and in deriving initial linguistic units from calls, a process far more dubious than the derivation of home-sign from naive gesture.

According to a “selective” (as opposed to “instructive”) model of human language capacity, people come to know more than they experience. The discrepancy between experience and eventual capacity (the “poverty of the stimulus”) is bridged by genetically provided information. Hence any hypothesis about the linguistic genotype (or “Universal Grammar,” UG) has consequences for what experience is needed and what form people's mature capacities (or “grammars”) will take. This BBS target article discusses the “trigger experience,” that is, the experience that actually (...) affects a child's linguistic development. It is argued that this must be a subset of a child's total linguistic experience and hence that much of what a child hears has no consequence for the form of the eventual grammar. UG filters experience and provides an upper bound on what constitutes the triggering experience. This filtering effect can often be seen in the way linguistic capacity can change between generations. Children only need access to robust structures of minimal (“degree-0”) complexity. Everything can be learned from simple, unembedded “domains” (a grammatical concept involved in defining an expression's logical form). Children do not need access to more complex structures. (shrink)

Wilkins & Wakefield's identification of anatomical features in the Koobi Fora endocast, which may be thought to carry some functional significance in relation to organization for language, raises fundamental problems of method: attention is drawn to some limitations of the evidence, of endocasts and of the neuroanatomical map used to interpret them.

The syntactic structures of natural languages reflect conceptual categories more directly than they reflect communicative categories. This fact supports the main premise of the target article, namely, that the most important event in language evolution was the development of a hierarchical conceptual structure.

Wilkins & Wakefield's intriguing model of language evolution is deficient in evidence of human uniqueness in metaphorical matching, amodal representation, reference, conceptual structure, hierarchical organization, linguistic comprehension, sign use, laterality, and handedness. Primates show communicative reference, laterality, and handedness, and apes in particular show hierarchical organization, conceptual structure, cross-modal abilities, sign use, and displaced reference.

Inferences made from endocasts of fossil skulls cannot provide information on the function of particular neocortical areas or the subcortical pathways to prefrontal cortex that form part of the neural substrate for speech, syntax, and certain aspects of cognition. The neural bases of syntax cannot be disassociated from “communication.” Manual motor control was probably a preadaptive factor in the evolution of humansyntactic ability, but neurophysiological data on living humans show that speech motor control and syntax are more closely linked. The (...) evolution of fully modern speech occurred fairly recently; thoughHomo habilismay have had some degree of speech and syntactic ability, it was not fully modern. Stone tools are uncertain indices of language or cognition. (shrink)

ProbablyHomo habilisis two species not one; similarly for Pan troglodytes. Although amenable to training, in naturePan paniscusmay be a “specialized insular dwarf.” Language is uniquely human, but symbolic behavior and intelligence are widespread among animals with little respect for phylogenetic closeness toHomo sapiens.

Representation must be prior to communication in evolution. Wilkins & Wakefield's target article gives the impression that communicative pressures play a secondary role. We suggest that their evolutionary precursor is compatible with protolanguage rather than language itself. The difference between these two communicative systems should not be underestimated: only the former can be trivially reappropriated from a representational system.

Contra Wilkins & Wakefield, we argue that an evolutionarily inspired approach to language must consider different facets of language (i.e., more than syntax and semantics), and must explore the possibility of nonhuman precursors. Several examples are discussed, illustrating the power of the comparative approach in illuminating our understanding of language evolution.

Wilkins & Wakefield suggest that changes in the hominid brain made it uniquely “preadaptive” for language, yet no precursor functions served as adaptive substrates to the emergence of language. We present contrary evidence that the ability to discriminate and process rapid and complex auditory information is a cross-species function subserving communication processes including, but not limited to, human speech perception. We suggest that auditory temporal processing served as an evolutionary precursor to speech processing and consequent language development in humans.

Hominid-like morphology in habiline cranial endocasts does not necessarily imply the presence of language capacity. The cortical zone in question is not associated exclusively with language in humans, and its emergence in habilines might indicate the evolution of other cognitive functions special to humans that were preconditions for the later evolution of language.

This response clarifies the nature of reappropriation and the definition of language. It explicates the relationship between neural systems and language and between homology and evolutionary gradualism. Through a review of ape capacities in the realms of language and tool use, it distinguishes human language acquisition from nonhuman learning. Finally, it suggests the appropriate sorts of evidence on which to base further evolutionary arguments relevant to the origins of language.

This target article presents a plausible evolutionary scenario for the emergence of the neural preconditions for language in the hominid lineage. In pleistocene primate lineages there was a paired evolutionary expansion of frontal and parietal neocortex (through certain well-documented adaptive changes associated with manipulative behaviors) resulting, in ancestral hominids, in an incipient Broca's region and in a configurationally unique junction of the parietal, occipital, and temporal lobes of the brain (the POT). On our view, the development of the POT in (...) our ancestors resulted in the neuroanatomical substrate consistent with the ability for representations in modality-neutral association cortex and, as a result of structure-imposing interaction with Broca's area, the hierarchically structured Evidence from paleoneurology and comparative primate neuroanatomy is used to argue that Homo habilis (2.5–2 million years ago) was the first hominid to have the appropriate gross neuroanatomical configuration to support conceptual structure. We thus suggest that the neural preconditions for language are met in H. habilis. Finally, we advocate a theory of language acquisition that uses conceptual structure as input to the learning procedures, thus bridging the gap between it and language. (shrink)

Wilkins & Wakefield are clearly right to separate linguistic capacity from communicative ability, if only because other animal species have one without the other. But I question the abruptness of the demarcation they make between a period when hominids evolved enriched conceptual representation for other reasons entirely, and a subsequent later stage when language use became an adaptation.

Understanding how conceptual structures inform stone tool production and use would help us resolve the issue of a pongid-hominid dichotomy in brain organisation and cognitive ability. Evidence from ideational apraxia suggests that the planning of linguistic and manipulative behaviours is not colocalized in homologous circuits. An alternative account in terms of the evolutionary expansion of the whole prefrontal-premotor area may be more plausible.

Many people have argued that the evolution of the human language faculty cannot be explained by Darwinian natural selection. Chomsky and Gould have suggested that language may have evolved as the by-product of selection for other abilities or as a consequence of as-yet unknown laws of growth and form. Others have argued that a biological specialization for grammar is incompatible with every tenet of Darwinian theory – that it shows no genetic variation, could not exist in any intermediate forms, confers (...) no selective advantage, and would require more evolutionary time and genomic space than is available. We examine these arguments and show that they depend on inaccurate assumptions about biology or language or both. Evolutionary theory offers clear criteria for when a trait should be attributed to natural selection: complex design for some function, and the absence of alternative processes capable of explaining such complexity. Human language meets these criteria: Grammar is a complex mechanism tailored to the transmission of propositional structures through a serial interface. Autonomous and arbitrary grammatical phenomena have been offered as counterexamples to the position that language is an adaptation, but this reasoning is unsound: Communication protocols depend on arbitrary conventions that are adaptive as long as they are shared. Consequently, language acquisition in the child should systematically differ from language evolution in the species, and attempts to analogize them are misleading. Reviewing other arguments and data, we conclude that there is every reason to believe that a specialization for grammar evolved by a conventional neo-Darwinian process. (shrink)