Long arcuate fascicle in wild and captive chimpanzees as a potential structural precursor of the language network
Yannick Becker, Cornelius Eichner, Michael Paquette, Christian Bock, Cédric Girard‐Buttoz, Carsten Jäger, Tobias Gräßle, Tobias Deschner, Bala Amarasekaran, Caroline Asiimwe, Daniel Aschoff, Martina Bleyer, Julian Chantrey, Pawel Fedurek, Karina Flores, Zoro Bertain Gone Bi, Jennifer E. Jaffe, Susan Hambrech, Daniel Hanus, Daniel Haun, Evgeniya Kirilina, Kathrin Kopp, Fabian H. Leendertz, Matyas Liptovszky, Patrice Makouloutou-Nzassi, Kerstin Mätz-Rensing, Richard McElreath, Matthew McLennan, Zoltan Mezö, Sophie Moittié, Torsten Møller, Markus Morawski, Karin Olofsson-Sannö, Simone Pika, Andrea Pizarro, Kamilla Pléh, Jessica Rendel, Alejandra Romero Forero, Jonas Steiner, Mark F. Stidworthy, Lara Southern, Claudia A. Szentiks, Tanguy Tanga, Reiner Ulrich, Steve Unwin, Sue Walker, Nikolaus Weiskopf, Gudrun Wibbelt, Kim Wood, Klaus Zuberbühler, Philipp Gunz, Roman M. Wittig, Catherine Crockford, Angela D. Friederici, Alfred Anwander
Abstract
The arcuate fascicle (AF) is the main fibre tract in the brain for human language. It connects frontal and temporal language areas in the superior and middle temporal gyrus (MTG). The AF's connection to the MTG was considered unique to humans and has influenced theories of the evolution of language. Here, using high-resolution diffusion MRI of post-mortem brains, we demonstrate that both wild and captive chimpanzees have a direct AF connection into the MTG, albeit weaker than in humans. This finding challenges the notion of a strictly human-specific AF morphology and suggests that language-related neural specialisation in humans likely evolved through gradual evolutionary strengthening of a pre-existing connection, rather than arising de novo. It is likely that this neural architecture supporting complex communication was already present in the last common ancestor of hominins and chimpanzees 7 million years ago, enabling the evolution of language processes in the human lineage.