The Arcuate Fascicle Middle Temporal Gyrus Connection in Chimpanzees: A Missing Link in Language Evolution?

Abstract

This forum article investigates the theoretical implications of the latest findings regarding the evolution of the arcuate fascicle (AF), the main white matter fibre tract for language. Thanks to ultra-high-resolution post-mortem tractography, a weak, left-lateralised connection between the inferior frontal gyrus and the middle temporal gyrus (MTG) connection was demonstrated in wild and captive chimpanzees. This proposed white matter substrate for the Faculty of Language in the Narrow sense (FLN) was previously thought to be unique to humans along with FLN itself. This finding suggests that the last common ancestor of humans and chimpanzees already possessed this neural architecture, casting into doubt the idea of a saltatory, human-specific emergence. The AF-MTG connection may therefore represent a missing link in language evolution, with strength and lateralisation that may have increased during human evolution, pointing to a more continuous evolution of language.