In Central Andes, exploitation of marine resources and introduction of intensive agriculture caused population size to increase early in its prehistory. Also, since its prehistory, there were constant movements of people in the Andes due to vertical use of the ecosystem, series of state expansions, forced migration by Inca, and migration to larger cities after European contact. These events probably had great effects on the genetic variation, but what extent these event influenced genetic variation is still uncertain. In this post, I reviewed recent mtDNA data from Central Andes to address these questions.
Following Tarazona-Santos et al. (2001), Fuselli et al. (2003) argues that mtDNA data supports Y chromosome data and Western part of South America, mainly Andes, and Eastern part of South America, mainly Amazon, had separate evolutionary histories. The Andean populations have high within-population genetic diversity and they are genetically similar to each other. They argue that both large effective population size and gene flow contributed for large within-population genetic diversity. The Amazonian populations, on the other hand, have low within-population genetic diversity and they are genetically differentiated, because without gene flow, genetic drift had a great effect on geographically isolated small populations.
Lewis et al. (2005, 2007) analyzed mtDNA sequence variation of five highland Peruvian populations and compared to two of three highland Peruvian populations that Fuselli et al. (2003) analyzed and lowland populations. Supporting the argument that Fusellli et al. put forth, Lewis et al. found high within-population genetic diversity among highland Peruvian populations and Andeans populations were genetically homogeneous compared to Amazonian populations. However, their AMOVA results suggest that there is no significant genetic difference between Andean group and Amazonian group. Lewis and Long (2008) found more mtDNA variation in Eastern South American and less genetic variation in the Andean region than previously reported, when regional variation was accounted for.
Analyses of mtDNA variation among the populations that occupy in the transitional zone between Andes and Amazon provide more complicated perspectives on the South American evolutionary history. Bert et al. (2004) and Corella et al. (2007) analyzed mtDNA variation of lowland Bolivians from the Department of Beni and Cabana et al. (2006) analyzed that of Gran Chaco. In general, these populations have genetic diversity values intermediate of Andean and Amazonian populations and they are genetically differentiated from each other. These patterns are expected from smaller relatively isolated populations.
However, they found evidence suggesting that these populations were not reproductively isolated and there were gene flows among these populations as well as between Andeans and populations in the transitional zone responding to state expansion from Andean highland or reorganization of indigenous societies during the colonial era. First, some of these small populations from lowland Bolivia have unexpectedly high within-population genetic diversity. Second, when the Ayoreo is excluded from analyses, Gran Chaco populations were very homogeneous. Finally, some these populations are genetically very similar to Andeans.
The population size in Central Andes may have been large enough for them to be genetically more diverse than other populations in South America, but the constant movements, or interactions, of people made populations in Central Andes genetically homogeneous and potentially genetically more diverse. This interaction sphere may have extended into the transitional zones making populations from the transitional zone genetically diverse and similar to Central Andeans. My review of articles on Central Andeans mtDNA variation, however, shows that no one has examined whether female effective population size or gene flow contribute more on mtDNA variation of these populations.
Cabana, G. S., D. A. Merriwether, et al. (2006). “Is the genetic structure of Gran Chaco populations unique? Interregional perspectives on native South American mitochondrial DNA variation.” American Journal of Physical Anthropology 131(1): 108-119.
Corella, A., F. Bert, et al. (2007). “Mitochondrial DNA diversity of the Amerindian populations living in the Andean Piedmont of Bolivia: Chimane, Moseten, Aymara and Quechua.” Annals of Human Biology 34(1): 34-55.
Tarazona-Santos, E., D. R. Carvalho-Silva, et al. (2001). “Genetic Differentiation in south amerindians is related to environmental and cultural diversity: Evidence from the Y chromosome.” American Journal of Human Genetics 68(6): 1485-1496.