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Four populations of Brazilian Indians were studied demographically and genetically. Overall, their estimated average ages are low, but the Kanamari are somewhat older. Intermixture with non-Indians is small, and intertribal marriages are seen mostly among the Katukina. Migration to the Central Pano (Cashinawa + Katukina) communities occurred mainly from southern places located at an average distance of 150 km. Migration to the Kanamari can be characterized as centripetal, taking place from communities situated at a mean distance of 235 km. Fertility and mortality are high. These results were integrated with genetic marker data and three indices of population variability (one based on demographic variables and the other two on genetic factors) calculated for them and four other South American tribes. These indices showed no significant relationships among themselves. It is suggested that such comparisons should be extended to populations biologically more differentiated, in attempts to unravel the intricate connections that exist between population structure and genetic variability.