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Human cranial diversity and their evolutionary implications

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Author(s):
Danilo Vicensotto Bernardo
Total Authors: 1
Document type: Doctoral Thesis
Press: São Paulo.
Institution: Universidade de São Paulo (USP). Instituto de Biociências (IBIOC/SB)
Defense date:
Examining board members:
Walter Alves Neves; Sabine Eggers; Sergio Danilo Junho Pena
Advisor: Walter Alves Neves
Abstract

The last decades have seen a growing number of contributions to the understanding of when and where was the emergence of Homo sapiens. Models based on this evidence generally suggests that the genesis of modern humans occurred in Africa some 200,000 years before present, where migrated to other parts of the world. Analysis of genetic diversity of current populations corroborate this scenario, suggesting that, from a single source, the species was gradually losing variability as the populations diverged, spatially and temporally, from each other and from their African ancestors. With regard specifically to the cranial morphology, several authors suggest the existence of this same pattern of decreasing variability as a function of distance from Africa, although it is also recognized among experts partition the human cranial diversity between two fundamental patterns: one represented by morphology similar to that characterized the first Homo sapiens before the process raciação in the sense diversifying, occurred, represented by the so-called \"general morphology\" and the other represented by other morphological variations, corresponding to the populations already been diversified Africa, called \"specialized morphology.\" In this sense, understanding the evolutionary processes involved in the events of morphological differentiation generates a lot of controversy among experts. Although most of the information already obtained point to the fact that the cranial morphology evolved mostly by stochastic processes, some evidence suggests that, at least in extreme environmental conditions, some cranial specific anatomical regions have a portion of their morphological variability determined by natural selection. In this context, the primary objective of this research is to characterize the evolution of human cranial variation, approached from two themes: 1) The investigation of the composition, pattern of occurrence, distribution and structuring of human cranial morphological diversity, and, 2) analysis of the context of evolutionary change observed in the human skull, due to its characteristics of integration, modularity and evolutionary stasis investigated from the exploitation of their patterns of variance and covariance. For this, we used the metric cranial characteristics (24 variables protocol Howells) of 9287 individuals distributed in 161 indigenous peoples worldwide dispersion. Only morphologically intact individuals constituted the database, eliminating any effect due to the occurrence of \"missing values\". Additional information on these series in the database were used to better characterize geographic and chronological these populations, and that allowed the calculation of geographical distances between them and the stratification of the data under different criteria. Databases additional compounds by molecular markers (mtDNA and microsatellites) were also used for exploratory comparative analysis of specific issues. The results for the analyzes of the composition, structure and distribution of human cranial diversity show that particular population groups, usually associated with a specific geographic region, provide diversification patterns different from those observed for all populations analyzed jointly, suggesting the occurrence of specific evolutionary responses associated with particular conditions, such as selection, for example. Regarding investigations of evolutionary context of the variation observed, inferred by patterns of correlation, covariance and modularity investigated in different population groups, the results generated showed that, in general, the patterns of variance / covariance and magnitude of correlation patterns between characters are presented in a stable manner, with rare exceptions the state of evolutionary stasis predominant. In summary, the results obtained through the different strategies employed in this thesis reinforce the idea that the evolution of cranial morphology is best explained by a model that assumes the occurrence of different evolutionary dictates, as genetic drift and natural selection, for example, that due to the recent process of diversification of species present in a generalized way, in a state of stasis (AU)