How has the human skull evolved?
The study is based on the analysis of 390 decorated skulls from the ossuary in Hallstatt (Austria) [Credit: University of Barcelona] |
A map with the coordinates of 29 anatomical landmarks
According to the results of the study, the evolutionary potential of the human skull is formally constrained by the relatively high morphological integration of the different skull structures. "In this type of evolutionary scenario, it would be different to change or alter one element without also altering the others," explains Miquel Hernà ndez.
"Traditionally, experts have studied how selection acts on a specific trait. In practice, however, the various traits are all inter-related. The key concept is morphological integration: if we change one of the elements in the shape of the skull the overall structure also changes, and only those changes that follow the morphological pattern are favoured."
The study examines the three-dimensional coordinates of 29 anatomical ‘landmarks’ in the human skull [Credit: University of Barcelona] |
The experts applied geometric morphometric and quantitative genetic methods to examine human skull shape, using the three-dimensional coordinates of 29 anatomical 'landmarks' to create morphological maps and simulating a range of scenarios in which different key traits are selected during the evolutionary process of modern humans: the forward shift of the foramen magnum, flexion of the cranial base, retraction of the face and enlargement of the neurocranium. Although it was long believed that these traits evolve separately -- through selection for bipedalism, dietary changes and encephalization -- the results of this new study suggest that they are strongly integrated and that the developed of each trait may have favoured the evolution of the others.
Individual traits do not evolve independently
The study calls for a reinterpretation of modern human evolutionary scenarios. As the lecturer Mireia Esparza explains, "Evolution acts as an integrated process and specific traits never evolve independently. In the case of the skull, evolutionary changes have converged to this morphological pattern. Therefore, we cannot simplify things and study the selection response of single trait in isolation, since although it is likely to have been affected by the selective factor in question, it is also constrained by the factors affecting other parts of the skull."
In human genealogies, each trait evolves gradually but within a pattern of strong morphological integration built on powerful genetic foundations. "This functional, operational morphological pattern should not be considered a negative restriction. If we think about disorders affecting cranial development, for example, the pattern of integration could constrain the variation to keep it within the limits of a functional framework," concludes the researcher Neus MartÃnez-AbadÃas.
The study was conducted in association with the Catholic church of Hallstatt (Austria), the Wenner Gren Foundation for Anthropological Research (USA) and the Spanish Ministry of Education and Science.
Source: University of Barcelona [December 20, 2011]
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