The present paper studies the evolutionary process operating on prehistoric groups from the Azapa valley and coast (northern Chile). The sample consists of 237 crania from the Archaic Late, Early Intermediate, Middle, Late Intermediate, and Late periods. Six metric variables were used, which were transformed to eliminate the special environmental component and to increase the proportion of genetic variance. Population structure was assessed using a method based on quantitative genetic theory, which predicts a lineal relationship between average within-group phenotypic variance and group distance to the population centroid. Results indicate that 17.5% of the total variance accounts for special environmental variance. An excess in extraregional genetic flow is observed in the population corresponding to the Early Intermediate period in the valley. A reduced differentiation is observed between Archaic and Early Intermediate coastal groups, as well as between the latter and the inhabitants of the valley in the same period. Genetic differences between both areas increased substantially since the Middle period. Evidence indicates that long-range gene flow was lower on the coast than in the valley, the lowest estimated Fst being 0.0199 for the total population (coast and valley), 0.0111 for the coastal population, and 0.0057 for the valley. Results are discussed in terms of regional archeological and ethnohistorical evidence, and a microevolutionary model is presented to account for the biological history of the population.

Mahalanobis D2 statistics (with size and shape components) were computed for nine craniometric variables among five prehistoric groups representing steps in the microevolutionary history of a coastal population in Northern Chile. Roughly 80% of craniometric variation was found to be explained by chronologic distance covering a period of roughly 6500 years. Kinship decreases in this population at a relatively constant rate of 8.6 X 10(-5) per year.

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.

Multivariate distance statistics were computed from 14 nonmetrical cranial variables among five prehistoric samples representing steps in the microevolutionary history of a coastal population in northern Chile. Roughly 70% of nonmetrical cranial variation was found to be explained by chronologic distance covering a period of 6,500 years. This estimate is similar to a previous one derived from craniometric data. Implications of these findings are briefly discussed.

ResumenEl propósito de este trabajo es caracterizar una población representativa del salar de Atacama durante el Período Medio y los posibles flujos poblacionales asociados al fenómeno Tiwanaku. Para ello, la colección de cráneos del cementerio arqueológico Coyo Oriente, depositada en el Museo Arqueológico de San Pedro de Atacama, fue sometida a análisis osteológicos determinándose sexo, edad y deformación craneana. Estos análisis se aplicaron a la totalidad de la colección, así como a las tres zonas del cementerio diferenciadas por Le Paige, las que representarían una secuencia cronológica de ocupación. Además se realizó el análisis comparativo entre dos grupos (supuestamente uno local y otro foráneo) determinados por el componente textil del sitio publicado por Oakland en 1992.Palabras claves: San Pedro de Atacama -Coyo Oriente -Período Medio -Tiwanaku -osteología -deformación craneana. AbstractThe aim of this paper is to characterize one of the Atacama basin's representative populations of the Middle Period and the possible arrival of foreign groups associated to Tiwanaku expansion. The cranial collection from the Coyo Oriente cemetery, housed at the Museo Arqueológico de San Pedro de Atacama, was hence analyzed for its sex, age and intentional deformation patterns. These analyses were applied to the entire collection as well as to the three mortuary zones of the cemetery identified by Le Paige, that would represent a chronological occupation sequence. Further comparison between the two groups (one supposedly local, the other foreign) was achieved by means of the sites' textile component, as described by Oakland in 1992.