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).

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.

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.

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.

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.

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 fall short of solving the language origin puzzle because they underestimate the cognitive and linguistic capacities of great apes. A focus on ape capacities leads to the recognition of varied levels of cognition and language and to a gradualistic model of language emergence in which early hominid language skills exceed those of the apes but fall far short of those of modern humans or later fossil hominid groups.

Three issues are addressed in this commentary. (1) Wilkins & Wakefield are commended for placing the complex behavior they discuss within an evolutionary matrix. (2) They err on a number of points in regard to their treatment of this complex behavior. These involve (a) their emphasis on the evolution of conceptual structure rather than language, (b) their equation of meaning with reference, (c) their minimalist view of learning theory, and (d) their separation of the evolution of speech from that of (...) language. (3) They adopt a framework for neural preconditions that has been clearly discredited on both behavioral and neuroanatomical grounds. Finally, recent research involving modern neuroimaging techniques casts further doubt on the authors' postulated functions for the neural areas they discuss. (shrink)