Cranial shape and size variation in human evolution: structural and functional perspectives

Abstract

A GLIMPSE INTO MODERN PALEOANTHROPOLOGY: In the last decades, paleoanthropology has been deeply modified, changing from a descriptive and historical science to a more quantitative and analytical discipline. The covariation of multiple traits is investigated to study the evolutionary changes of the underlying anatomical models, mostly through the introduction of digital biomedical imaging procedures and of computed geometrical analyses supported by multivariate statistics. FUNCTIONAL CRANIOLOGY: The evolution of the human cranium is consequently considered in terms of functional and structural relationships between its components, largely influenced by the allometric variations associated with the increase in the relative cranial capacity. In the human genus, the changes in the face, base, and neurocranium are characterised by a mosaic variation, in which adaptations, secondary consequences, and stochastic factors concur to generate a set of anatomical possibilities and constraints. SYSTEMIC PERSPECTIVES TO THE EVOLUTION OF THE HUMAN CRANIAL MORPHOLOGY: Concepts like morphological modularity, anatomical integration, and heterochrony represent key issues in the development of the current human evolutionary studies.

Cortical Folding of the Primate Brain: An Interdisciplinary Examination of the Genetic Architecture, Modularity, and Evolvability of a Significant Neurological Trait in Pedigreed Baboons (GenusPapio)

“…The utility of CT-based virtual endocasts for studies of primate brain evolution, including in examination of cortical-folding features, has been validated in both anthropology and paleoneurobiology (Zollikofer et al 1998;Bruner 2003Bruner , 2004Bruner , 2007Bruner , 2008Zollikofer and de León 2005;Carlson et al 2011;Balzeau et al 2012;Falk 2014;Kobayashi et al 2014). Our measurements taken on these CT scan-based virtual endocasts showed extremely high repeatability (average = 93%), implying reliable and consistent data collection.…”

Applying Craniofacial Metrics to Adapt 3D Generic Head Models

“…However, simply analyzing the diameters of the cranium is an older technique used to study cranial evolution. Contrastingly, the current analysis of spatial relationships between different anatomical structures can be applied to inter-and intra-ethnic comparisons (Bruner, 2007). We can alter pre-existing individual realistically-shaped head models by applying translation, rotation, scaling, warping, or applying more advanced metrics such as elliptical and power functions (Figs.…”

“…While deriving multiple generic head models, we can use stochastic factors to generate a set of anatomical possibilities and constraints to prevent subsequent models with nonhuman and atypical human shapes and sizes. A more encompassing approach would make use of a multivariate analysis of 2D and 3D anatomical features across numerous models (Bruner, 2007). Furthermore, these analyses and constraints can be applied not only to wide-ranging generic head models but additionally to various ethnic groups to create subpopulation-specific generic models.…”

“…Bruner (2007) investigated the evolution of the cranium through the scope of allometry, indicating that the size and shape of the skull changes due to adaptations as well as stochastic factors. They attributed the increase in volumetric cranial capacity as one of the primary factors affecting the cranial shape.…”

“…Whether we reference our current universal base model or these three representative racial base models, mathematical congruency associated with growth will have the same effect Bruner (2007 Howells (1973). Contrastingly, our exponential and elliptical transformation of our universal caucasian model across racial types does not fully exhibit the cranial or facial metrics of the new (target) ethnic groups of the target racial type.…”