The evolution of verbal behavior in children.

Introduction Complex language is one of the unique repertoires of the human species. Others include teaching and certain "types of imitation" (Premack, 2004), although these too may be pre-or co-requisites for certain functional uses of language. Over the last 40 years linguists have proposed theories and provided evidence related to their interpretation of the structure of language (Chomsky, 1959; Chomsky & Place, 2000, MacCorquodale, 1970; Pinker, 1999). Neuroscientists have identified neurological correlates associated with some aspects of language (Deacon, 1979, Holden, 2004). Behavior analysts have focused on the source of and controlling variables for the function of language as behavior per se (Catania, Mathews, & Shimoff, 1990; Greer & Ross, 2005; Michael, 1984; Skinner, 1957). More recently, scholars have come to view human language as a product of evolution; "Linguists and neuroscientists armed with new types of data are moving beyond the non-evolutionary paradigm once suggested by Noam Chomsky and tackling the origins of speech head-on." (Culotta & Brooks-Hanson, 2004, p. 1315). The current work focuses on the evolution of both the non-oral motor and oral components of speech (Deacon, 1997; Holden, 2004), although some arguments are characterized necessarily more by theory than data. Despite the evidence that primates and pigeons can be taught certa in features of verbal behavior (D. Premack & A. Premack; 2003; Savage-Rumbaugh, Rumbaugh, & Boysen, 1978; Epstein, Lanza, & Skinner, 1980), the speaker-as-own listener capability makes complex verbal behavior possible and may represent what is most unique about human verbal functions (Barnes-Holmes, Barnes-Holmes, & Cullinan, 2001; Lodhi & Greer, 1989; Horne & Lowe, 1996). Some suggest that oral communication evolved from clicking sounds to sounds of phonemes, and cite the extant clicking languages as evidence (Pennisi, 2004). It is likely that sign language and gesture predated both vocal forms; but it is the evolution of the spoken and auditory components of language that are seen as critical to the evolution of language. Some of these include changes in the anatomy of the jaw--Homo sapiens have more flexible jaw than did Neanderthals. Also, the location of the larynx relative to the trachea is different for Homo sapiens, and this anatomical feature made it possible for the humans to emit a wider range of speech sounds (Deacon, 1997). The combination of these anatomical changes, together with the identification of separate, but proximate, sites in the brain for speaking, listening, and imitation seem to be critical parts of what made spoken language possible (Deacon, 1997). The presence of these anatomical and physiological properties made it possible for the evolution of verbal functions through the process of cultural selection (Catania, 2001). The functional effects of speech sounds were acquired by the consequences provided within verbal communities. This latter focus is what constitutes the subject matter of verbal behavior. The new foci on language, as an evolved anatomical and physiological capacity, do not necessarily suggest the existence of a universal grammar; nor, in fact, does it eliminate the possibility of an evolved universal grammar, as some argue (Pinker, 1999). Some of the linguistic neuropsychological searches for an evolved universal grammar now follow the PET and MRI trails and focus on identifying blood flow associated with the speech and hearing centers in the brain (Holden, 2004). Interesting and as important as this work may be, little, if any, is devoted to the function of language as behavior per se. Nor is it concerned with the biological or cultural evolution of verbal function in our species or in the lifespan of the individual, although anthropological linguists point to functions as the initial source. Only the research associated with Skinner's (1957) theory of verbal behavior as behavior per se, and expansions of the theory by contemporary behavior analysts, provide the means for analyzing how cultural selection gave rise to the function of language (Greer, 2002; Greer & Ross, in press; Hayes, Barnes-Holmes, & Roche, 2000; Lowe, Horne, Harris, & Randle, 2002). …