Measuring the impact of European colonization on Native American populations in Southern Brazil and Uruguay: Evidence from mtDNA.

OBJECTIVES: The major aim of this article was to estimate the demographic impact of European arrival and colonization over Native American populations from southern Brazil and Uruguay. We also compared the mitochondrial DNA (mtDNA) genetic diversity, structure, and demography of Native American lineages present in current indigenous (Natives) and nonindigenous admixed (Admixed) populations to estimate the effective population size (Ne ) of contemporary and ancestral (pre-Columbian) Native American populations. METHODS: We retrieved published mtDNA sequences from Native (n = 396) and Admixed (n = 309) populations from southern Brazil, Uruguay, and surrounding areas. We conducted genetic diversity, structure, and demographic analyses. Finally, we used Approximate Bayesian Computation to estimate the Ne for current Native, Admixed, and pre-Columbian Native American populations. RESULTS: We found higher Native American mtDNA genetic diversity in admixed rather than in indigenous populations (131/309 vs 27/396 different haplotypes, respectively). Only Admixed populations maintained ancient signals of the Native American population expansion approximately 14 to 17 kya, which have decayed in Natives. Our Ne estimates suggest that Natives represent only 0.33% (0.18%-1.19%) of the Ne for ancestral pre-Columbian indigenous populations. CONCLUSIONS: Admixed populations represent an important genetic reservoir of Native American lineages, many of which are extinct in contemporary indigenous populations. In addition, the Native American lineages present in Admixed populations retain part of the past demographic history of Native Americans. The intensity of the reduction is congruent with historical accounts of strong indigenous depopulation during the colonization process.

Opening the Implicit Leadership Theories' Black Box: An Experimental Approach with Conjoint Analysis.

Although research on implicit leadership theories (ILTs) has concentrated on determining which attributes define a leadership prototype, little attention has been paid to testing the relative importance of each of these attributes for individuals' leadership perceptions. Building on socio-cognitive theories of impression processes, we experimentally explore the formation of leadership perceptions based on the recognition of six key attributes in a series of three experimental studies comprising 566 US-based participants recruited online via Amazon Mechanical Turk. Our results show that while certain attributes play an important role in the leader categorization process, others are less relevant. We also demonstrate that some attributes' importance is contingent on the presence of other attributes and on the leadership schema type activated in respondents' minds. Consistent with the Leadership Categorization Theory, our findings support the premise that individuals cognitively hold a superordinate leadership prototype, which imposes constraints on their more basic level prototypes. We discuss the implications of these results for leadership theory and practice.