The emergence of language in the hominin lineage : perspectives from fossil endocasts

Abstract

Since brain does not fossilize, brain endocast (i.e., replica of the inner surface of the braincase, Figure ​Figure1)1) constitutes the only direct evidence for reconstructing hominin brain evolution (Holloway, 1978; Holloway et al., 2004a). In this context, paleoneurology has suffered from strong limitations due to the fragmentary nature of the fossil record and the absence of any information regarding subcortical elements in extinct taxa. Additionally, variation in brain shape and organization (and in the corresponding endocast) is technically difficult to capture, as stated by Bruner (2017a, p. 64): “[…] the smooth and blurred geometry of the brain, its complex and complicated mechanisms, and its noticeable individual variability make any research associated with its morphology very entangled and difficult to develop within fixed methodological approaches.” An emblematic example might be the reluctance of paleoneurologists to consider the sulcal imprints visible on the endocranial surface because of the substantial uncertainties in describing such features in fossil specimens and related debates (e.g., the lunate sulcus in the Taung child's endocast; Falk, 1980a, 2009, 2014; Holloway, 1981a; Holloway et al., 2004b). In 1987, Tobias even came to the conclusion that “The recognition of specific cerebral gyri and sulci from their impressions on an endocast is a taxing, often subjective and even invidious undertaking which arouses much argumentation” (p. 748). However, in conjunction with a conceptual shift toward a more comprehensive overview of hominin brain evolution (e.g., reconsideration of the “cerebral rubicon” characterizing the human brain, Falk, 1980b; Holloway, 1983), continuous discoveries of new fossil material and recent analytical developments are progressively improving and refining our knowledge about the human neural evolutionary history. In particular, paleoneurology is producing new evidence for reconstructing the timing and mode of the emergence of crucial functions, such as language.