Broca's Area - Evolution of Language

Evolution of Language

The pursuit of a satisfying theory that addresses the origin of language in humans has led to the consideration of a number of evolutionary "models." These models attempt to show how modern language might have evolved, and a common feature of many of these theories is the idea that vocal communication was initially used to complement a far more dominant mode of communication through gesture. Human language might have evolved as the "evolutionary refinement of an implicit communication system already present in lower primates, based on a set of hand/mouth goal-directed action representations." "Hand/mouth goal-directed action representations" is another way of saying "gestural communication", "gestural language", or "communication through body language." The recent finding that Broca's area is active when people are observing others engaged in meaningful action is evidence in support of this idea. It was hypothesized that a precursor to the modern Broca's area was involved in translating gestures into abstract ideas by interpreting the movements of others as meaningful action with an intelligent purpose. It is argued that over time the ability to predict the intended outcome and purpose of a set of movements eventually gave this area the capability to deal with truly abstract ideas, and therefore (eventually) became capable of associating sounds (words) with abstract meanings. The observation that frontal language areas are activated when people observe Hand Shadows is further evidence that human language may have evolved from existing neural substrates that evolved for the purpose of gesture recognition. The study, therefore, claims that Broca's area is the "motor center for speech", which assembles and decodes speech sounds in the same way it interprets body language and gestures. Consistent with this idea is that the neural substrate that regulated motor control in the common ancestor of apes and humans was most likely modified to enhance cognitive and linguistic ability. Studies of deaf "speakers" of American Sign Language and English speakers suggest that the human brain recruited systems that had evolved to perform more basic functions much earlier; these various brain circuits, according to the authors, were tapped to work together in creating language.

Another recent finding has showed significant areas of activation in subcortical and neocortical areas during the production of communicative manual gestures and vocal signals in chimpanzees . Further, the data indicating that chimpanzees intentionally produce manual gestures as well as vocal signals to communicate with humans suggests that the precursors to human language are present at both the behavioral and neuronanatomical levels. More recently, the neocortical distribution of activity-dependent gene expression in marmosets provided direct evidence that the ventrolateral prefrontal cortex, which comprises Broca’s area in humans and has been associated with auditory processing of species-specific vocalizations and orofacial control in macaques, is engaged during vocal output in a New World monkey . These findings putatively set the origin of vocalization-related neocortical circuits to at least 35 million years ago, when the Old and New World monkey lineages split.