Human Paleoneurology and the Evolution of the Parietal Cortex

Abstract

Paleoneurology deals with the study of brain anatomy in fossil species, as inferred from the morphology of their endocranial features. When compared with other living and extinct hominids, Homo sapiens is characterized by larger parietal bones and, according to the paleoneurological evidence, also by larger parietal lobes. The dorsal elements of the posterior parietal cortex (superior parietal lobules, precuneus, and intraparietal sulcus) may be involved in these morphological changes. This parietal expansion was also associated with an increase in the corresponding vascular networks, and possibly with increased heat loads. Only H. sapiens has a specific early ontogenetic stage in which brain form achieves such globular appearance. In adult modern humans, the precuneus displays remarkable variation, being largely responsible for the longitudinal parietal size. The precuneus is also much more expanded in modern humans than in chimpanzees. Parietal expansion is not influenced by brain size in fossil hominids or living primates. Therefore, our larger parietal cortex must be interpreted as a derived feature. Spatial models suggest that the dorsal and anterior areas of the precuneus might be involved in these derived morphological variations. These areas are crucial for visuospatial integration, and are sensitive to both genetic and environmental influences. This article reviews almost 20 years of my collaborations on human parietal lobe evolution, integrating functional craniology, paleoneurology, and evolutionary neuroanatomy.

Inter-individual Variability of Functional Connectivity in Awake and Anesthetized Rhesus Monkeys

“…In considering overall patterns of regional differences in the present work, it is worth noting their relations to phylogenetic ordering, with heteromodal association areas emerging later in the evolutionary process (35)(36)(37)(38). Leading hypotheses (e.g., the tethering hypothesis) emphasize the contributions of environmental factors (e.g., molecular gradients), and their interactions with genetically-determined processes, to the cortical expansions that led to the development of heteromodal association areas (39).…”

Storage of Information and Its Implications for Human Development: A Dialectic Approach

“…These were possibly self-reinforcing, since these developments could help secure the energy needs of a larger brain and a larger brain could also lead to more diversity in and capacity for cultural and technological development (Sterelny, 2010;Antón and Snodgrass, 2012;Galway-Witham et al, 2019). Indeed, there is evidence that modern behavior stabilized 150,000 years ago, around the time that the parietal lobe also reached its current dimensions (Schlebusch et al, 2017;Bruner, 2018;Neubauer et al, 2018;Davies, 2019). Thus, the development of storage of information was not simply a result of encephalisation (growth of brain size), but required the evolution of different social systems, "such as the extension of scale of ranging areas and interaction networks, the appearance of social norms relating to information and its transfer, or the use of material cultural symbols as information stores" (Steele and Shennan, 1996, p. 26).…”

Body Cognition and Self-Domestication in Human Evolution

“…In Homo sapiens , this process is thought to have enabled an expanded cooperative ability, leading to improved language and knowledge-sharing, thereby promoting social complexity and technological advancement (Hare, 2017; Thomas and Kirby, 2018). Humans are also characterized by an outstanding capacity for integration between brain, body and tools, and the evolution of this ability is associated with neuroanatomical changes of the visuospatial association cortex (Bruner, 2018). Whilst current scholarship is yet to address the potential for interaction between self-domestication and body cognition, we hypothesize that there may be value in an examination of any overlap.…”