This commentary supports MacNeilage's dismissal of an evolutionary development from sign language to spoken language but presents evidence of a feature in sign language (echo phonology) that links iconic signs to abstract vocal syllables. These data provide an insight into possible mechanism by which iconic manual gestures accompanied by vocalisation could have provided a route for the evolution of spoken language with its characteristically arbitrary form–meaning relationship.

This commentary deals with the relation between human language and nonverbal signals used by nonhuman primates. It suggests that human language could have developed through the interaction of procedural learning with a preexisting system for socio-affective communication. The introduction of “content” into existing “frames” requires a neurobiologically plausible learning mechanism.

We describe a possible link between coordinated lateralised group behaviour serving species survival in lower vertebrates and a striking lateralisation phenomenon found in human social behaviour: the universal preference for cradling a young infant on the left side. Our exploration offers a different perspective on the role of cerebral asymmetry for the survival of both the individual and the species.

Evidence from studies of the processing of topographic and classifier constructions in sign language sentences provides a model of how a mental scene description can be represented linguistically, but it also raises questions about how this can be related to spatial linguistic descriptions in spoken languages and their processing. This in turn provides insights into models of the evolution of language.

Although gestures have surface similarities with language, there are significant organisational and neurolinguistic differences that argue against the evolutionary connection proposed by Corballis. Dominance for language and handedness may be related to a basic specialisation of the left cerebral hemisphere for target-directed behaviour and sequential processing, with the right side specialised for holistic-environmental monitoring and spatial processing.