Vol 1 | 2007
Cornell Synapse
REVIEW The evolution of language in Homo sapiens Kevin K. Kumar
Cornell University, Department of Neurobiology and Behavior, Ithaca, NY 14853
The dawn of language in Homo sapiens is still uncharted territory in the scope of human evolution. Language, the audible, articulate, meaningful sound as produced by the action of the vocal organs, is a complex behavior displayed only in H. sapiens. The power of language is the primary basis of the complex society humans have created, serving as a means of human communication. This form of communication does not exist at the human level of complexity among other organisms, but evidences of similar evolution exist in other species. The role of FOX genes in humans and other vertebrates pinpoints a key moderator in development, and provides insight into this moderator’s evolutionary origin. The selection pressures which favored the evolution of language, likely also favored neural and motor facility growth. Unparalleled in evolutionary influence, language not only allowed a species to express basic observations of the physical world, but also what an individual thinks. The facility to speak imposes a great deal of demands on an organism’s anatomical structures. In order for one to vocalize, syntactic, semantic, phonological and pragmatic representations as well as motor and sensory systems must be coordinated (Fisher and Marcus 2006). The requirements for this level of coordination are stemmed in nervous system development, particularly the cerebral cortex. The cerebral cortex is the center of all language mediating functions. In addition to the focus in the cerebral cortex, language capacity is broadly distributed across cortical and subcortical circuits across the brain (Lieberman 2002). The great demand on the nervous system can be best appreciated through looking at the very complexity of language. Language is composed of a system of syllables and words which can be combined to produce and infinite combination of ideas. The first step in identifying how language emerged in H. sapiens is to identify the regions mediating language in the modern human mind. In particular, two regions of the brain, the Broca’s and Wernicke’s areas, located in the temporal gyrus, are believed to play a significant role in language (Innocenti and Price 2005). Broca’s area is primarily responsible for speech production and grammar, whereas Wernicke’s area is essential to meaning and understanding. Diseases and injuries affecting these areas confirm these roles (Fisher and Marcus 2006). For instance, those suffering from Broca’s aphasia, a legion in the Broca’s area, have difficulty articulating sentences. Conversely, those suffering from Wernicke’s aphasia can speak articulately and rapidly but lack continuity of topic mid-sentence. Although these areas play a vital ©2007 Cornell Synapse | www.cusn.org
role in language, their role is not absolute. Not all legions to these particular regions lead to symptoms of the aphasia, suggesting that language relies on a larger neural network outside the Broca’s and Wernicke’s areas (Fisher and Marcus 2006). These cortical regions share homologues with primates, suggesting that the adaptations which facilitate language are based on the asymmetric brain structure of a recent common ancestor of H. sapiens and apes. One must consider how large scale changes in human evolution left the mechanisms through which language develops intact. No region of the brain is restricted by one particular function; there are critical bodily functions also performed in these areas. Therefore, one can conclude that the development of language facility in the brain must have had flexibility in language mediating centers, while maintaining a level of stability which performs normal functions. One could also note that while it is important to focus on neural structure and development, attention should be paid to the development of the mechanics of speech: vocalization and pronunciation. The general ability to generate simple speech such as grunts and noises was present before his specificity of language. However, there is a widely held belief that specialization in the larynx occurred alongside neural development (Arbib 2005). The dawn of language did not occur independently, certain selection pressures favored language development. Developments in the cerebral cortex, both in size and complexity, were likely caused by selection pressures which favored the development of new functions as well as the maintenance of old ones. Evolutionary cortical adaptations increased behavioral specialization and the level of cognitive thinking, attributes which in effect increased the fitness of those individuals. The two largest ends selection pressures favored were increased motor skills and social behavior (Corballis 1992). The relationship between these two skills is exemplified by the intimate proximity of regions moderating these behaviors within the brain. In addition, both the ability to perform complex motor tasks and complex communication are rooted in brain lateralization (Arbib 2005). Brain lateralization is a highly level neural adaptation which increases both the range and efficiency of tasks which can be performed. The evolutionary mechanism, through which neural adaptations such as lateralization emerged, is based on overproduction and selection of connections in development (Innocenti and Price 2005). This theory, demonstrates that the brain merely did not specialize overnight into a language mediating powerhouse, but gradually through intense selection generated the neural complexity neuron by neuron. The similarities, both genetic and molecular, between humans and their primate cousins reveal a great deal regarding the origin 11