Human paleoneurology: Shaping cortical evolution in fossil hominids

Abstract

Evolutionary neuroanatomy must integrate two different sources of information, namely from fossil and from living species. Fossils supply information concerning the process of evolution, whereas living species supply information on the product of evolution. Unfortunately, the fossil record is partial and fragmented, and often cannot support validations for specific evolutionary hypotheses. Living species can provide more comprehensive indications, but they do not represent ancestral groups or primitive forms. Macaques or chimpanzees are frequently used as proxy for human ancestral conditions, despite the fact they are divergent and specialized lineages, with their own biological features. Similarly, in paleoanthropology independent lineages (such as Neanderthals) should not be confused with ancestral modern human stages. In this comparative framework, paleoneurology deals with the analysis of the endocranial cavity in extinct species, in order to make inferences on brain evolution. A main target of this field is to distinguish the endocranial variations due to brain changes, from those due to cranial constraints. Digital anatomy and computed morphometrics have provided major advances in this field. However, brains and endocasts can be hard to analyze with geometrical models, because of uncertainties due to the localization of cortical landmarks and boundaries. The study of the evolution of the parietal cortex supplies an interesting case‐study in which paleontological and neontological data can integrate and test evolutionary hypotheses based on multiple sources of evidence. The relationships with visuospatial functions and brain–body–tool integration stress further that the analysis of the cognitive system should go beyond the neural boundaries of the brain.

A network approach to the topological organization of the Brodmann map

“…However, labeling brain areas is a methodological requirement to promote comparative and quantitative approaches in neuroanatomy. Many fields employ microanatomical or molecular traits (Glasser et al, 2016), while others necessarily rely on macroanatomical features (Bruner, 2019). Although Brodmann's map was based on microanatomical and histological aspects, it approximately matches macroanatomical boundaries, and for this reason it is often employed to pragmatically label macroscopic sulcal regions.…”

“…A network perspective, like the one presented in this article, allows to consider which areas are more sensitive to spatial constraints. Regions with complex topology and high morphological burden can change by virtue of intrinsic changes (increase/decrease of their absolute and relative volumes) but also because of secondary spatial constraints due to the neighboring elements (Bruner, 2019(Bruner, , 2021. In those cases, inferences on brain evolution based on the gross anatomy of sulci and gyri are more difficult to disentangle, and hypotheses on possible functional/ cognitive changes are more problematic to assess.…”

“…One of these fields is, for example, paleoneurology, namely the anatomical study of the endocranial cavity in fossils, aimed at investigating the evolution of brain morphology in extinct species (Bruner, 2017; Holloway et al, 2004). The localization of gyri and sulci on endocranial casts ( endocasts ), although with a degree of error, can reveal major changes of cortical proportions in different phylogenetic lineages (Bruner, 2019; De Jager et al, 2019). The localization of these features is necessarily based on gross anatomical traits of the cortical surface, and Brodmann's labels have been therefore commonly employed to design hypotheses in brain evolution.…”

The parietal lobe evolution and the emergence of material culture in the human genus

“…In evolutionary anthropology, the alternative to living species is the study of fossil specimens. In this case, we can detect (or at least suppose) ancestor-descendent changes, observing the process of evolution itself, instead of its product (Bruner 2019 ). However, also in this case there are important limitations: paleontological samples are generally very small, and inferences are based on few individuals represented only by scattered bony remains.…”

“…The parietal cortex is deeply involved in the cognitive integration between brain, body, and environment, and hence a specialization of its areas is expected in Homo sapiens , who represents the most technological and symbolic species ever evolved so far. It has been hypothesized that neural and cognitive changes have increased the prosthetic capacity of our species, namely the possibility to integrate tools and symbols in our body schemes and cognitive machinery, outsourcing information processing to external peripheral elements (Malafouris 2010 ; Iriki and Taoka 2012 ; Bruner 2019 , 2021 ). In this case, “mind” can be interpreted as a flow of information between brain, body, and material culture.…”