Maximum genetic proportion of metric traits from different regions of the skull in ancient humanpopulations of Northwestern Argentina

In order to explain the evolutionary process of ancient human populations that inhabited a specific geographical region from quantitative skull traits, it is advisable to know the evolutionary potential of metric characters. For this reason, the proportion of the maximum genetic variance or maximum heritability (h2m) of the variables studied was estimated. In addition, it was evaluated whether h2m changes between regions of the skull (face, base and vault) and the degree of association between the phenotypic variance and the maximum genetic variance. Twenty-one symmetrical variables on the left and right sides of the skull were measured in 245 skulls from five prehistoric samples from northwestern Argentina. The upper limit of heritability was estimated using the repeated measurement method. To test whether there are differences between the h2m of each group, the Kruskal-Wallis test was used. The maximum genetic values of each variable were obtained through a regression analysis (right measure on left measure). The relationship between phenotypic and maxi-mum genetic values was evaluated by correlation analysis. Significant bilateral difference is demon-strated in six of 21 characters. The average h2m is 0.77 and ranges between 0.58 and 0.93. The aver-age correlation between phenotypic values and maximum genotypic values was 0.8 (R2=0.65), suggesting that it is possible to make inferences of the genetic structure of the population from phenotypic information. The high proportion of maximum observed genetic variance indicates an important evolutionary potential of the craniofacial complex in ancient populations of northwestern Argentina

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Coastal, valley, and oasis interaction: impact on the evolution of ancient populations in the South Central Andes.

The existing biocultural links are analyzed among ancient inhabitants of the Cochabamba valleys (Bolivia) from the Formative and Tiwanaku periods, coastal and inland Azapa region (Chile) from the Late Archaic to the Late periods, and the Atacama Desert oases (Chile) from the Formative period to the time of European contact. Craniometric information obtained from a sample of 565 individuals from different sites of the studied regions was evaluated using methods derived from quantitative genetics and multivariate statistical analysis techniques. It is shown that during the Formative and Tiwanaku periods inhabitants of the Cochabamba valleys maintained contact with the population of northern Chile. This contact was more fluid with the people from the interior valley of Azapa than it was with the settlers of San Pedro Atacama (SPA). An important biological affinity in the Late Period between the inhabitants of the Azapa valley and the late SPA groups is also examined. The Late-Inca Catarpe SPA sample shows a broad genetic variability shared with the majority of the groups studied. The results reaffirm the differences between the coastal and interior Azapa valley groups and strengthen the hypothesis of two pathways to populating the south central Andean area. The divergence observed among subpopulations can be explained by the spatiotemporal dispersion between them, genetic drift dispersion compensated by the action of gene flow, and cultural norms that regulate within group mating.

The genetic divergence of prehistoric populations of the south-central Andes as established by means of craniometric traits.

The peopling of the south-central Andean region can be determined by exploring a combination of cultural, economic, and biological factors that influence the structure of populations and determine particular dispersals of gene frequencies. Quantitative characters from 1,586 adult crania of both sexes from northern Chile, northwestern Argentina, and the Cochabamba valleys in Bolivia were analyzed employing multivariate statistical analyses. Biological distances, representing phenotypic variation between these regions and their subregions, were studied within a population genetics framework. An analysis of Mahalanobis D(2) distances establishes two principle directions of interaction: the first between the Cochabamba valleys and northern Chile, and the second between the Cochabamba region and northwestern Argentina. The Chile and Argentina regions are shown to be less related to each other than each is to the Bolivian region. A higher mean genetic divergence is found for the entire region (F(ST) = 0.195); with northwestern Argentina having the highest spatial isolation (F(ST) = 0.143) and northern Chile the lowest (F(ST) = 0.061). These results allow us to propose a populating model based on the dispersion of several lines from a common ancestral population similar to those who inhabited the Cochabamba valleys. These lines differentiated themselves in time and space according to the effective size and the rate of gene flow, eventually producing the human groups which inhabited the valleys of northern Chile and northwestern Argentina.