Evolution of the Central Mechanisms of Oral Speech

Abstract

The communicative system is most developed in social animals and represents a determinative factor in human evolution. Here we address the possible evolutionary ways of the emergence and formation of speech functions. Specifically, we discuss the possibility of the formation of voluntary voice control at the early stages of Homo evolution on the anatomo-physiological basis of the gesture control system. The possible morphofunctional basis for the evolutionary emergence of speech is considered. The structure and connectivity of different regions of the cerebral cortex (temporal, inferior, parietal) are compared in humans and monkeys. Anatomy of the auditory cortex is well known to be relatively alike in different primate species, likewise are the pathways that link the auditory cortex with the associative areas of the anterior temporal cortex and the ventrolateral prefrontal cortex (human homologs of these structures form the ventral speech stream). At the same time, the pathways that link the auditory cortex with the ventral premotor and inferior motor cortex and make up in humans the dorsal speech stream are poorly developed in monkeys. The underdevelopment of this speech stream accounts for communication in monkeys based on gestural speech, because the morphological basis for voluntarily regulated vocalization and articulation has not yet formed during their evolution. The emergence of a sophisticated communication system based on oral speech may have been possible due to a gradual accumulation of evolutionary changes in speech-related and some other brain structures and, most importantly, a complication of connectivity between them. The evolution of speech is discussed in terms of its close association with tool use and labor activity.