by Kaitlyn May
Friederici (2017) provides a comprehensive review of research exploring the evolution of language. By reviewing structural and functional neuroanatomical differences between the primate and mature human brain, as well as comparisons between the phylogenesis and ontogenesis of language-relevant brain structures, Friederici provides a relevant timeline of the neural basis of language evolution while highlighting the specific aspects of language and neural structures which underpin this ability.
Friederici begins with a brief overview of the differing ways in which researchers define language. This then moves into a complex discussion of the computational mechanisms for human language. Though this section may be a bit daunting to those who are not well-versed in the language literature, Friederici does an admirable job breaking down difficult topics. Essentially, some researchers define language as all aspects of communication (facial expressions, hearing language, processing, etc.) while others focus specifically on the computational mechanisms behind how language is built. It is this construction aspect, and the complications of advanced grammar, that separates nonhuman primates from humans.
Friederici then begins reviewing studies of the neural mechanisms of human language. These studies overview differences in acquiring grammar systems in human and nonhuman primates, as well as the neurobiological bases of these grammar types. These studies conclude that the ability to master phrase structure grammar is uniquely human. Moreover, these studies highlight the neural mechanisms of language processing. Friederici first overviews the role of the posterior portion of Broca’s area (Brodmann area [BA 44]) in not only syntactic hierarchy building, but in the evolutionary pathway of language. Next, Friederici discusses the role of the inferior frontal gyrus, posterior temporal cortex, and the white matter fiber bundles connecting them to processing syntactically complex sentences.
The paper then moves into a review of cross-species comparisons of language. To date, there is no evidence that other species can process and learn hierarchically structured sequences. Friederici begins by noting that the posterior temporal cortex is larger in the left than the right hemisphere of both the human and chimpanzee brain, reflecting the left lateralization of language. In contrast, Broca’s area demonstrates distinct differences between cytoarchitecture, asymmetry, and developmental trajectories of human and nonhuman primates. Moreover, the dorsal pathway, a crucial pathway for the language ability in adult humans, is much weaker in nonhuman primates than in humans. These differences are postulated to reflect the behavioral trajectories in child language development as well as the lack of these behaviors in nonhuman primates. Friederici concludes that the differing asymmetries may be crucial to understanding the evolution of language.
Friederici (2017) provides an in-depth review to the neural circuits underlying the evolutionary pathway towards human language. Although does an excellent job reviewing a large body of relevant studies, the author neglects to include studies which indicate abilities of nonhuman primates to acquire human language skills, such as those in which chimpanzees learn to use American Sign Language (ASL). Although these studies typically admit limitations in the nonhuman primates abilities, they are still noteworthy to the evolution of language. Still, what Friederici does do nicely is provide a comprehensive understanding of the exact piece of language which is distinctly human—the ability to process and learn hierarchically structured sequences.
Reference: Friederici, A. D. (2017). Evolution of the neural language network, Psychonomics Bulletin and Review, 24, 41-47.