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.

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.

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.

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.

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.

The precise manner in which language serves its communicative function suggests that natural selection, rather than exaptation or reappropriation, played the major role in its evolution. Natural selection is more readily invoked, I suggest, if it is assumed that language originated as a system of manual gestures, and later switched to an oral mode.

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.

In the present study, using event-related functional magnetic resonance imaging, we investigated a group of participants on a grammaticality classification task after they had been exposed to well-formed consonant strings generated from an artificial regular grammar. We used an implicit acquisition paradigm in which the participants were exposed to positive examples. The objective of this studywas to investigate whether brain regions related to language processing overlap with the brain regions activated by the grammaticality classification task used in the present study. (...) Recent meta-analyses of functional neuroimaging studies indicate that syntactic processing is related to the left inferior frontal gyrus (Brodmann's areas 44 and 45) or Broca's region. In the present study, we observed that artificial grammaticality violations activated Broca's region in all participants. This observation lends some support to the suggestions that artificial grammar learning represents a model for investigating aspects of language learning in infants [TICS 4 (2000) 178] and adults [Proceedings of the National Academy of Sciences of United States of America 99 (2002) 529]. (shrink)

Several claims made by Wilkins & Wakefield require qualification. First, the proposed delineation of the parietal-occipital-temporal junction (POT) is overly restrictive. Second, focusing exclusively on the evolutionary importance of manual manipulation oversimplifies interacting evolutionary preconditions for language. Finally, Wilkins and Wakefield's perspective adheres to a homocentric, formal, linguistic definition of language instead of viewing language as a multimodal sensory enhancement system unique to each species.

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.

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.

This commentary criticizes Wilkins & Wakefield's thesis that the neurological precursors of language provide a cognitive Rubicon to linguistically divide human from nonhuman primates. A causal model of their theory is presented, followed by a discussion of the relationship between brain expansion and tool use, Broca's area and the parietaloccipital-temporal junction (POT).

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.

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.

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)

This commentary confronts one of the central tenets advanced in Wilkins & Wakefield's target article: By adopting a very narrow perspective on language, the authors have effectively limited discussion of earlier linguistic capabilities thought to be at least facilitative of, if not prerequisite to language defined as a An alternative conceptualization for describing semiogenesis is offered.

If POT (parieto-occipital-temporal junction) reorganization came earlier in australopithecines than in Homo, it is likely that the selective pressures were different, and not necessarily directed toward language. The brain endocast evidence for the POT in A. afarensis is actually better than it is for early Homo.

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.

Wilkins and Wakefield's hypothesis that language is fundamentally a cognitive rather than cominunicational adaptation is reasonable, but there are flaws in their anatomical and fossil evidence. Their analysis of reorganization also needs clarification. Finally, the origin of language ability must have occurred with australopithecine rather than habiline adaptations on entry into the novel hominid adaptive zone.

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.

The species-specific organizational property of speech is a continual mouth open-close alternation, the two phases of which are subject to continual articulatory modulation. The cycle constitutes the syllable, and the open and closed phases are segments framescontent displays that are prominent in many nonhuman primates. The new role of Broca's area and its surround in human vocal communication may have derived from its evolutionary history as the main cortical center for the control of ingestive processes. The frame and content components (...) of speech may have subsequently evolved separate realizations within two general purpose primate motor control systems: (1) a motivation-related medial system, including anterior cingulate cortex and the supplementary motor area, for self-generated behavior, formerly responsible for ancestral vocalization control and now also responsible for frames, and (2) a lateral system, including Broca's area and surround, and Wernicke's area, specialized for response to external input (and therefore the emergent vocal learning capacity) and more responsible for content. (shrink)