Wednesday, May 18, 2011

Relationship between skull patterns and genes.

Here are 4 peer reviewed studies which show how cranio-facial patterns indicate genetic ancestry and similarity.


Race and global patterns of phenotypic variation

Relethford et al (2009).

"Phenotypic traits have been used for centuries for the purpose of racial classification. Developments in quantitative population genetics have allowed global comparison of patterns of phenotypic variation with patterns of variation in classical genetic markers and DNA markers. Human skin color shows a high degree of variation among geographic regions, typical of traits that show extensive natural selection. Even given this high level of geographic differentiation, skin color variation is clinal and is not well described by discrete racial categories. Craniometric traits show a level of among-region differentiation comparable to genetic markers, with high levels of variation within populations as well as a correlation between phenotypic and geographic distance. Craniometric variation is geographically structured, allowing high levels of classification accuracy when comparing crania from different parts of the world. Nonetheless, the boundaries in global variation are not abrupt and do not fit a strict view of the race concept; the number of races and the cutoffs used to define them are arbitrary. The race concept is at best a crude first-order approximation to the geographically structured phenotypic variation in the human species."
SOURCE : Relethford, J. H. (2009), Race and global patterns of phenotypic variation. American Journal of Physical Anthropology, 139: 16–22. doi: 10.1002/ajpa.20900

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Congruence of individual cranial bone morphology and neutral molecular affinity patterns in modern humans


Noreen von Cramon-Taubadel et al (2009).

Abstract

"Recent studies have demonstrated that the shape of the human temporal bone is particularly strongly correlated with neutral genetic expectation, when compared against other cranial regions, such as the vault, face, and basicranium. In turn, this has led to suggestions that the temporal bone is particularly reliable in analyses of primate phylogeny and human population history. While several reasons have been suggested to explain the temporal bone's strong fit with neutral expectation, the temporal bone has never systematically been compared against other individual cranial bones defined using the same biological criteria. Therefore, it is currently unknown whether the shapes of all cranial bones possess reliable information regarding neutral genetic evolution, or whether the temporal bone is unique in this respect. This study tests the hypothesis that the human temporal bone is more congruent with neutral expectation than six other individual cranial bones by correlating population affinity matrices generated using neutral genetic and 3D craniometric data. The results demonstrate that while the temporal bone shows the absolute strongest correlation with neutral genetic data compared with all other bones, it is not statistically differentiated from the sphenoid, frontal, and parietal bones in this regard. Potential reasons for the temporal bone's consistently strong fit with neutral expectation, such as its overall anatomical complexity and/or its contribution to the architecture of the basicranium, are examined. The results suggest that future phylogenetic and taxonomic studies would benefit from considering the shape of the entire cranium minus those regions that deviate most from neutrality."
SOURCE : Von Cramon-Taubadel N (in press) Congruence of individual cranial bone morphology and neutral molecular affinity patterns in modern humans. Am J Phys Anthropol. doi 10.1002/ajpa.21041.

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The questionable contribution of the Neolithic and the Bronze Age to European craniofacial form


C. Loring Brace et al (2005).

"Many human craniofacial dimensions are largely of neutral adaptive significance, and an analysis of their variation can serve as an indication of the extent to which any given population is genetically related to or differs from any other. When 24 craniofacial measurements of a series of human populations are used to generate neighbor-joining dendrograms, it is no surprise that all modern European groups, ranging all of the way from Scandinavia to eastern Europe and throughout the Mediterranean to the Middle East, show that they are closely related to each other."
SOURCE : C. Loring Brace et al. The questionable contribution of the Neolithic and the Bronze Age to European craniofacial formProc Natl Acad Sci U S A. 2006 January 3; 103(1): 242–247. Published online 2005 December 21. doi: 10.1073/pnas.0509801102

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Characterization of biological diversity through analysis of discrete cranial traits

Hanihara et al. (2003)

"In the present study, the frequency distributions of 20 discrete cranial traits in 70 major human populations from around the world were analyzed. The principal-coordinate and neighbor-joining analyses of Smith's mean measure of divergence (MMD), based on trait frequencies, indicate that 1). the clustering pattern is similar to those based on classic genetic markers, DNA polymorphisms, and craniometrics;2). significant interregional separation and intraregional diversity are present in Subsaharan Africans; 3). clinal relationships exist among regional groups; 4). intraregional discontinuity exists in some populations inhabiting peripheral or isolated areas. For example, the Ainu are the most distinct outliers of the East Asian populations. These patterns suggest that founder effects, genetic drift, isolation, and population structure are the primary causes of regional variation in discrete cranial traits. Our results are compatible with a single origin for modern humans as well as the multiregional model, similar to the results of Relethford and Harpending ([1994] Am. J. Phys. Anthropol. 95:249-270). The results presented here provide additional measures of the morphological variation and diversification of modern human populations. Copyright 2003 Wiley-Liss, Inc."
SOURCE : HANIHARA, TSUNEHIKO, HAJIME ISHIDA, AND YUKIO DODO. 2003. Characterization of biological diversity through analysis of discrete cranial traits. American Journal of Physical Anthropology 121:241-251.

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