Fig. 3.

Transition of brain capacity (ordinate) along the evolutionary processes of various ancestral pre-hominids and hominids (abscissa) [adapted from “Evolution Du Volume Cérébral Des Hominidés” (2016)]. Inset illustrations of skull and brain depict representative hominids plotted on the graph. Brain expansion suddenly accelerated when Homo habilis started to use stone tools (oblique red arrow), and it branched off from the regression line (orange solid line) for extant non-human primates including great apes (ca. Chimpanzees). Oldwan culture: the earliest widespread stone tools were simple, usually made with one or a few flakes chipped off with another stone, and used by Homo habilis. Acheulean culture: stone tool characterized by distinctive oval and pear-shaped “hand-axes” manufactured and used by Homo erectus. Simple syntax of vocal communication, a primitive form of human language, is thought to be required for the transmission of this culture. Mousterian culture: techno-complex and symbolic archaeological industry of fling lithic technologies associated with Homo sapiens neanderthalensis throughout early Homo sapiens sapiens. Insets along top-left edges are diagrams illustrating different principles of brain organization between rodents (left; middle to bottom) and primates (top; left to right) [adapted from Dooley and Krubitzer (2013) and Krubitzer (2009)]. Colored areas in brain illustrations indicate primary sensory (red: somatosensory; blue: visual; yellow: auditory) areas in representative extant primate and rodent species of body (first numbers in brackets) and brain (last numbers in brackets) sizes. Note the difference in proportion of these primary areas and association areas (in white) in different sized brains between primates and rodents