The Farming/Language Dispersal Hypothesis posits that prehistoric population expansions, precipitated by the innovation or early adoption of agriculture, played an important role in the uneven distribution of language families recorded across the world. In this case, the most widely spread language families today came to be distributed at the expense of those that have more restricted distributions. In the Americas, Uto-Aztecan is one such language family that may have been spread across Mesoamerica and the American Southwest by ancient farmers. We evaluated this hypothesis with a large-scale study of mitochondrial DNA (mtDNA) and Y-chromosomal DNA variation in indigenous populations from these regions. Partial correlation coefficients, determined with Mantel tests, show that Y-chromosome variation in indigenous populations from the American Southwest and Mesoamerica correlates significantly with linguistic distances (r = 0.33-0.384; P < 0.02), whereas mtDNA diversity correlates significantly with only geographic distance (r = 0.619; P = 0.002). The lack of correlation between mtDNA and Y-chromosome diversity is consistent with differing population histories of males and females in these regions. Although unlikely, if groups of Uto-Aztecan speakers were responsible for the northward spread of agriculture and their languages from Mesoamerica to the Southwest, this migration was possibly biased to males. However, a recent in situ population expansion within the American Southwest (2,105 years before present; 99.5% confidence interval = 1,273-3,773 YBP), one that probably followed the introduction and intensification of maize agriculture in the region, may have blurred ancient mtDNA patterns, which might otherwise have revealed a closer genetic relationship between females in the Southwest and Mesoamerica.mtDNA | Uto-Aztecan | Y chromsome | maize | migration

The initial contact of European populations with indigenous populations of the Americas produced diverse admixture processes across North, Central, and South America. Recent studies have examined the genetic structure of indigenous populations of Latin America and the Caribbean and their admixed descendants, reporting on the genomic impact of the history of admixture with colonizing populations of European and African ancestry. However, relatively little genomic research has been conducted on admixture in indigenous North American populations. In this study, we analyze genomic data at 475,109 single-nucleotide polymorphisms sampled in indigenous peoples of the Pacific Northwest in British Columbia and Southeast Alaska, populations with a well-documented history of contact with European and Asian traders, fishermen, and contract laborers. We find that the indigenous populations of the Pacific Northwest have higher gene diversity than Latin American indigenous populations. Among the Pacific Northwest populations, interior groups provide more evidence for East Asian admixture, whereas coastal groups have higher levels of European admixture. In contrast with many Latin American indigenous populations, the variance of admixture is high in each of the Pacific Northwest indigenous populations, as expected for recent and ongoing admixture processes. The results reveal some similarities but notable differences between admixture patterns in the Pacific Northwest and those in Latin America, contributing to a more detailed understanding of the genomic consequences of European colonization events throughout the Americas.

Anthropological studies suggest that the genetic makeup of human populations in the Americas is the result of diverse processes including the initial colonization of the continent by the first people plus post-1492 European migrations. Because of the recent nature of some of these events, understanding the geographical origin of American human diversity is challenging. However, human parasites have faster evolutionary rates and larger population sizes allowing them to maintain greater levels of genetic diversity than their hosts. Thus, we can use human parasites to provide insights into some aspects of human evolution that may be unclear from direct evidence. In this study, we analyzed mitochondrial DNA (mtDNA) sequences from 450 head lice in the Americas. Haplotypes clustered into two well-supported haplogroups, known as A and B. Haplogroup frequencies differ significantly among North, Central and South America. Within each haplogroup, we found evidence of demographic expansions around 16,000 and 20,000 years ago, which correspond broadly with those estimated for Native Americans. The parallel timing of demographic expansions of human lice and Native Americans plus the contrasting pattern between the distribution of haplogroups A and B through the Americas suggests that human lice can provide additional evidence about the human colonization of the New World.

Ancient DNA from the bone remains of 25 out of 28 pre-Columbian individuals from the Late Classic-Postclassic Maya site of Xcaret, Quintana Roo, was recovered, and mitochondrial DNA (mtDNA) was amplified by using the polymerase chain reaction. The presence of the four founding Amerindian mtDNA lineages was investigated by restriction analysis and by direct sequencing in selected individuals. The mtDNA lineages A, B, and C were found in this population. Eighty-four percent of the individuals were lineage A, whereas lineages B and C were present at low frequencies, 4% and 8%, respectively. Lineage D was absent from our sample. One individual did not possess any of the four lineages. Six skeletons out of 7 dated from the Late Classic period were haplotype A, whereas 11 skeletons out of 16 dated from the Postclassic period were also haplotype A. The distribution of mtDNA lineages in the Xcaret population contrasts sharply with that found in ancient Maya from Copán, which lack lineages A and B. On the other hand, our results resemble more closely the frequencies of mtDNA lineages found in contemporary Maya from the Yucatán Peninsula and in other Native American contemporary populations of Mesoamerican origin.

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