Abstract
Recent studies from the field of language genetics and evolutionary anthropology have put forward the hypothesis that the emergence of our species-specific brain is to be understood not in terms of size, but in light of developmental changes that gave rise to a more globular braincase configuration after the split from Neanderthals-Denisovans. On the grounds that (i) white matter myelination is delayed relative to other brain structures and, in humans, is protracted compared with other primates and that (ii) neural connectivity is linked genetically to our brain/skull morphology and language-ready brain, I argue that one significant evolutionary change in Homo sapiens’ lineage is the interhemispheric connectivity mediated by the Corpus Callosum. The size, myelination and fiber caliber of the Corpus Callosum present an anterior-to-posterior increase, in a way that inter-hemispheric connectivity is more prominent in the sensory motor areas, whereas “high- order” areas are more intra-hemispherically connected. Building on evidence from language-processing studies that account for this asymmetry (‘lateralization’) in terms of brain rhythms, I present an evo-devo hypothesis according to which the myelination of the Corpus Callosum, Brain Asymmetry, and Globularity are conjectured to make up the angles of a co-evolutionary triangle that gave rise to our language-ready brain.
Highlights
The general aim of this paper is to support the idea that the key underlying our human- specific cognitive profile is to be found in the changes that brought about a more globular brain shape
While Hublin et al (2015) concentrate mostly on the evolutionary and developmental facet of the problem, Boeckx and Benítez-Burraco, 2014a,b; Benítez-Burraco and Boeckx, 2015) mainly focus on the link between globularity and language on a genetic level: their positing that the fronto-parieto-thalamic network might be of relevance seems to reflect the great majority of the findings that implicate the fronto
The hypothesis I wish to put forward is the following: it is the structure of the Corpus Callosum that makes humans’ brains display a sophisticated, selective asymmetry: in the anterior/medial cortex, where callosal fibers are narrow and intrahemispheric connectivity is enhanced, asymmetry is expressed at the level of small- world networks, i.e., cognitive functions appear to be lateralized as modules; in the posterior cortex, there is no such asymmetry, as visual, auditory, and motor functions appear in both hemispheres
Summary
The general aim of this paper is to support the idea that the key underlying our human- specific cognitive profile is to be found in the changes that brought about a more globular brain shape.
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