title: Acquisition of Paleolithic toolmaking abilities involves structural remodeling to inferior frontoparietal regions.
abstract: Human ancestors first modified stones into tools 2.6 million years ago, initiating a cascading increase in technological complexity that continues today. A parallel trend of brain expansion during the Paleolithic has motivated over 100 years of theorizing linking stone toolmaking and human brain evolution, but empirical support remains limited. Our study provides the first direct experimental evidence identifying likely neuroanatomical targets of natural selection acting on toolmaking ability. Subjects received MRI and DTI scans before, during, and after a 2-year Paleolithic toolmaking training program. White matter fractional anisotropy (FA) showed changes in branches of the superior longitudinal fasciculus leading into left supramarginal gyrus, bilateral ventral precentral gyri, and right inferior frontal gyrus pars triangularis. FA increased from Scan 1-2, a period of intense training, and decreased from Scan 2-3, a period of reduced training. Voxel-based morphometry found a similar trend toward gray matter expansion in the left supramarginal gyrus from Scan 1-2 and a reversal of this effect from Scan 2-3. FA changes correlated with training hours and with motor performance, and probabilistic tractography confirmed that white matter changes projected to gray matter changes and to regions that activate during Paleolithic toolmaking. These results show that acquisition of Paleolithic toolmaking skills elicits structural remodeling of recently evolved brain regions supporting human tool use, providing a mechanistic link between stone toolmaking and human brain evolution. These regions participate not only in toolmaking, but also in other complex functions including action planning and language, in keeping with the hypothesized co-evolution of these functions.
authors.affiliation: Department of Anthropology, Emory University, 1557 Dickey Drive, Room 114, Atlanta, GA, 30322, USA, ehecht@gsu.edu.
authors.forename: E E
authors.initials: EE
authors.lastname: Hecht
authors.forename: D A
authors.initials: DA
authors.lastname: Gutman
authors.forename: N
authors.initials: N
authors.lastname: Khreisheh
authors.forename: S V
authors.initials: SV
authors.lastname: Taylor
authors.forename: J
authors.initials: J
authors.lastname: Kilner
authors.forename: A A
authors.initials: AA
authors.lastname: Faisal
authors.forename: B A
authors.initials: BA
authors.lastname: Bradley
authors.forename: T
authors.initials: T
authors.lastname: Chaminade
authors.forename: D
authors.initials: D
authors.lastname: Stout
mesh_terms: D000293:Adolescent; D000328:Adult; D005075:Biological Evolution; D001931:Brain Mapping; D005260:Female; D005625:Frontal Lobe / Q000033:anatomy & histology* / Q000502:physiology*; D006801:Humans; D007091:Image Processing, Computer-Assisted; D008279:Magnetic Resonance Imaging; D008297:Male; D009043:Motor Activity; D010296:Parietal Lobe / Q000033:anatomy & histology* / Q000502:physiology; D053001:Tool Use Behavior / Q000502:physiology*; D055815:Young Adult