The evolution of Broca's area

P. Thomas SCHOENEMANN, Indiana University and the Stone Age Institute

From an evolutionary perspective, anything as complex and adaptive as language would necessarily have evolved through exaptation: The modification of pre-existing anatomy and behavior. It is simply not credible to suggest that wholly new language-specific neural circuits would have evolved just for language. A full understanding of how language evolved therefore involves investigating homologous circuits in non-human animals that - in humans - subserve language, and to determine what these circuits are doing in these animals that led language to make use of – and ultimately fine-tune – these circuits during human evolution. One anatomical brain region that is known to be critical for language is Broca’s area, located in the inferior frontal convexity. Though first identified by Paul Broca in the 19^th century as language area, homologs have more recently been found in chimpanzees and at least one monkey species. What types of neural processing these homologs subserve in these species has not been extensively studied, though there are suggestions that it is involved in species-specific communication. Another way to probe its basic pre-human function(s) is to investigate non-language processing in Broca’s area in humans, and then to look for possible homologous types of processing in other species. For example: Broca’s area has been shown to be critical to learning non-linguistic sequential patterns in humans. This suggests a hypothesis: Broca’s area circuits first evolved to pay attention to – and ultimately learn – sequential pattern information (i.e., ‘rules’) from the organism’s environment. This talk will summarize the current state of research in my lab attempting test this hypothesis, both by assessing sequential pattern learning abilities in orang-utans at the Indianapolis Zoo (in collaboration with Robert Shumaker, Chris Martin, and colleagues), and through attempting to assess the overlap of processing of both non-linguistic sequential pattern learning vs. explicitly linguistic grammatical processing tasks. These studies hope to determine the extent to which Broca’s area has been modified over our evolutionary history to serve linguistic functions in modern humans: Did we evolve extensive new, highly language-specific circuitry in our Broca’s area, or do we use basically the same circuitry (perhaps enhanced to allow for more complex sequential patterns – of any kind) for both linguistic and non-linguistic functions? The long term goal of such studies is to help us better understand the role of behavior in driving biological evolution generally.