This book presents a unique range of interdisciplinary work on questions of language development and evolution. It makes visible the significant contribution which meaning-oriented linguistics is making to debates about the origins of language - from the perspective of language evolution in the species (viewed as the evolution of "meaning potential") as well as language development in the child (viewed as "learning how to mean"). As well as linguistics in the systemic functional, or Hallidayan, tradition, the book offers contributions from primatology, psychiatry, sociology and education. What the authors share is a view of language as a social semiotic system. By seeing language in this way, and drawing on actual language corpora, the authors are able to address major questions of deep social significance, including: * the roles grammar in the emergence of consciousness, from protolanguage to higher order consciousness * the dynamics of language variation, including semantic variation, in children's development * children's learning in and about a second language * the significance of different ways of talking about language for school literacy development * understanding borderline personality disorder from the perspective of language development