Evolutionary implications of vocal development in the first half-year of life

Vocal development, contextual flexibility, babbling The study of human infant vocal development has yielded new perspectives on how the capacity for speech is built, and has provided important suggestions about the paths that our hominid ancestors may have followed in evolution of speech. The research to be considered in this paper highlights a natural logic that characterizes the steps of vocal development in human infants. Important aspects of that natural logic appear to have applied to evolution of speech as well (see Oller & Griebel, 2005). The paper thus suggests a relation between ontogeny and phylogeny where, at least in key respects, both abide by a common logic pertaining to the possible ways that a powerful vocal communication system might be built. It has been argued previously that a critical first step in establishing a foundation for a speech capacity in primates is the evolution of a substantially higher degree of “contextual flexibility ” in vocalization (Oller, 2000; Oller & Griebel, 2005) than has been reported to occur in non-human primates (see Cheney & Seyfarth, 1999; Hauser, 1996). In general, non-human primates are seen to produce a small set of relatively stereotypical vocalizations each of which is relatively firml