Ancient Molecular and Morphometric Variation from Chile: The Death of the Dual-Entry Model?
Chungara, Revista de Antropología Chilena Vol. 43, No 2, 2011, pp. 283-292
Morphometric and mtDNA Analyses of Archaic Skeletal Remains from Southwestern South America
Germán Manríquez, Mauricio Moraga, Calogero Santoro, Eugenio Aspillaga, Bernardo T. Arriaza, and Francisco Rothhammer.
For decades anthropologists have discussed how and when the Americas were peopled. The prevailing view is that the first Paleoindians, ancestors of the Amerindians, arrived from Asia and Beringia to the American continent using a Pacific coastal route in pre-Clovis times. In this article skeletal remains dated 9000-4000 BP, excavated from archaeological sites in northern, central and southern Chile, were analyzed using geometric morphometric and ancient mtDNA techniques. Results indicate that the ancient cranial material from southwestern South America exhibit a wide range of cranial vault shape variation which is independent of chronology. mtDNA restriction and sequence analysis performed on the same skeletal remains, revealed only the presence of the main four founding mtDNA haplogroups (A, B, C and D) as early as 9,000 BP. Our results using morphometric and molecular mtDNA haplogroup data show that human populations inhabiting the Americas during archaic times can not be considered as belonging to two different groups on the basis of analyzed data. These results are consistent with those recently obtained using complete sequence mtDNA analyses.
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It’s a pleasure to blog about research published in lesser known scientific journals. Data published in peripheral sources is often unknown to the mainstream academic and amateur public in the U.S. and Europe. Introducing Chungara, a Chilean anthropological forum, and an article reporting on morphometric and mtDNA variation in a sample of 27 Early, Middle, and Late Archaic skulls from Northern, Central and Southern Chile dated at 9000-4000 BP. There are two key findings reported in this paper.
1. All four principal American Indian mtDNA markers (hgs A, B, C, D) were detected in the sample, which indicates the stability and diversity of genetic composition of South American Indians in pre-agricultural times. At the same time, haplogroup assignment is rather crude, as sublineage-specific SNPs weren’t screened for. Hg B was reported for the first time south of 43 degrees south latitude. It means it was present in the area by at least 8,000 BP but was subsequently lost there, as modern populations in southern South America don’t have it. This finding doesn’t make life easier for those scholars who continue to derive hg B from a separate migration into the New World, although in North America hg B is attested at 12,000 YBP (Paisley Cave). Also, previously hg A has never been reported in ancient remains earlier than 4,504 YBP.
2. Manríquez et al. (2012) failed to detect a division of skulls into two broad groups – the earlier “Australomelanesian” type and the later “Mongoloid” type. This division has been championed in the late 1990s-early 2000s by multiple teams of paleobiologists who interpreted the division as indicative of two migrations into the New World. (See, e.g., Neves, W. A., and M. Hubbe. 2005. “Cranial Morphology of Early Americans from Lagoa Santa, Brazil: Implications for the Settlement of the New World,” Proceedings of the National Academy of Sciences 102, 18309-18314). Instead, they observed a wide range of cranial variation which is independent of both chronology and geography (see below, Fig. 2).
The authors further note (p. 290) that
“…Considering the CI values as well as the geographical origin of the samples, and due to head length contribution, the skulls may be classified as dolichocephalic. This finding is consistent with he classical argument of South American physical anthropologists about the dolicocephalic morphology of most ancient skulls compared to more recent ones belonging to agricultural societies. However, when the shape and size components of cranial form are partitioned, the main “cephalic types” of classical physical anthropology are all well represented in the morphometric shape space (i.e. dolicocephalic, mesocephalic and brachicephalic ones), clustering independently of the chronological origin of the samples.”
The two morphological types construed by Walter Neves, Joseph Powell and other paleobiologists have always been hard to reconcile with the main finding from American Indian haploid genetics in the 1990s, namely that all principal mtDNA and Y-DNA types are evenly distributed across South, Central and North America (Merriwether, D. A., F. Rothhammer, and R. E. Ferrell. 1995. “Distribution of the Four Founding Lineage Haplotypes in Native Americans Suggests a Single Wave of Migration for the New World,” Am J Phys Anthropology 98 (4): 411-430). Ancient mtDNA obtained from early Holocene skulls failed to show stark molecular contrast between ancient and modern samples but confirmed the heterogeneity of ancient samples (Kemp B. M,. R. S. Malhi, J. McDonough, D. A. Bolnick, J. A. Eshleman. (2007) “Genetic Analysis of Early Holocene Skeletal Remains from Alaska and Its Implications for the Settlement of the Americas,” Am J Phys Anthropology 132: 605-621).
Proponents of the dual-migration theory acknowledge that theirs is not the only possible explanation of the observed split between ancient and recent American Indian skulls.
“This, however, does not completely exclude the possibility that the observed morphological diversity in America is the result of diachronic trends of differentiation, or progressive losses of the original variability present in the mother-population of Native Americans, especially if strong diversifying selection acted upon the morphological pattern brought into the continent by its first populations.” (Hubbe, M., W. A. Neves, K. Harvati. 2010. “Testing Evolutionary and Dispersion Scenarios for the Settlement of the New World,” PLoS ONE 5 (6): e11105.
Manriquez et al.’s data is consistent with these alternatives to the two-migration model. Pursuant of their data, they endorsed a single-wave model for the peopling of the Americas. However, this is not a throwback to the times when American Indian variation was perceived as unambiguously restricted and falling into a “Mongoloid” cluster. The reality behind the two divergent schools of thought on American Indian craniological variation, and this has largely come to light in the 1990s-2000s, is that American Indian skulls are exceptionally diverse, and that the “Mongoloid” type is just a subset of this broad variation found in the Americas. One should recall Peter Brown’s observation that “at present the earliest people with a generalised East Asian cranial morphology are probably found in the Americas. Is it a possibility that migration across the Bearing Straits went in two directions and the first morphological Mongoloids evolved in the Americas?”