Studies of population genetics are contributing some of the best evidence regarding prehistoric populations and migrations. We have many reasons to hope that as this research continues, it will help us refine and enhance our model in significant ways.
Why haven’t these studies revealed DNA evidence in support of our model yet?
There are numerous ways that DNA evidence might not be visible to modern studies, but we will save that discussion for another day. Today I want to point out the fact that, although a lot of DNA research is being conducted, these genetic studies are dismissing unexpected lineages. When their tests produce results that indicate genetic descent from other continents, those results are thrown out under the assumption that they are the result of sampling errors or modern population admixture.
For instance, only one single DNA study has ever been conducted to learn about the genetic history of the prehistoric inhabitants of the Baja Peninsula. The authors of the study tested DNA samples from twelve prehistoric skeletons from various areas in the peninsula. The results were a little disappointing to the researchers:
“Out of the twelve samples in the study only one sample, Sample 8: La Matancita Entiero Multi I-J was confirmed to contain amplifiable mtDNA. Sporadic amplification was obtained from Sample 4: Isla San Jose La Paz BCS Entiero 1, Sample 6: La Matancita BCS Entiero Multi I-G, and sample 10: El Conchalito La Paz Entiero 39, but none of these samples could be determined to belong to one of the common Native American haplogroups
(Genetic relationships of prehistoric Baja, California populations; Cara Monroe, Brian M. Kemp; 2008)
In other words, three of the four viable DNA samples were from lineages outside of the Americas so the authors dismissed them, assuming them to be the results of contamination.
A wonderful study of mtDNA in the southwest was published in 2013. They also came across unexpected results and assumed they were the result of modern admixture:
All individuals that did not belong to haplogroup A, B,C, D, or X were excluded from the analyses, as they most likely represent non-Native American admixture
(Exploring Prehistory in the North American Southwest with Mitochondrial DNA Diversity Exhibited by Yumans and Athapaskans; AMERICAN JOURNAL OF PHYSICAL ANTHROPOLOGY 150:618–631 (2013); Cara Monroe, Brian M. Kemp, and David Glenn Smith)
This was also how similar unexpected results were treated in 2003:
Altogether, 479 individuals…were analyzed in this study. Any individuals in a given sample determined not to belong to haplogroups A, B, C, D, or X were assumed to represent non-Native American admixture and were excluded from analysis.
(Native American mtDNA Prehistory in the American Southwest; Ripan S. Malhi, Holly M. Mortensen, Jason A. Eshleman, Brian M. Kemp, Joseph G. Lorenz, Frederika A. Kaestle, John R. Johnson, Clara Gorodezky, and David Glenn Smith)
And again in a 2010 study:
Data Analysis. For mtDNA analysis, all individuals that do not belong to haplogroup A–D or X (Table S1) were excluded, because they most likely represent non-Native American admixture.
(Evaluating the Farming/Language Dispersal Hypothesis with genetic variation exhibited by populations in the Southwest and Mesoamerica; PNAS, April 13, 2010 vol. 107 no. 15 6759–6764; Brian M. Kemp, Angélica González-Oliver, Ripan S. Malhi, Cara Monroeb, Kari Britt Schroeder, John McDonough, Gillian Rhett, Andres Resendéz, Rosenda I. Peñaloza-Espinosa, Leonor Buentello-Malo, Clara Gorodeskyk, and David Glenn Smith)
In contrast to these studies, another study in 2007 followed up on an unexpected lineage and discovered ancient DNA from a non-Native American haplogroup. They summed up my thoughts on this subject quite well:
Researchers studying mtDNA of contemporary populations may have ignored evidence of additional founding haplogroups because it did not fit the prevailing five-founder model for the peopling of the Americas. In addition, studies of ancient DNA in the Americas may have misidentified authentic evidence of additional founder lineages as contamination and, as such, failed to report the results.
(Mitochondrial haplogroup M discovered in prehistoric North Americans; Journal of Archaeological Science 34 (2007) 642e648; Ripan S. Malhi, Brian M. Kemp, Jason A. Eshleman, Jerome Cybulski, David Glenn Smith, Scott Cousins, Harold Harry)