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Top: dates of individuals with genetic data (individual 95.4% confidence intervals and total summed probability density; MHCP.19.12.17 [low-coverage] omitted for scale). *Date based on association with familial relative. Bottom: earliest radiocarbon dates associated with microbotanical evidence for maize, manioc, and chili peppers in the Maya region and adjacent areas at Lake Puerto Arturo, Guatemala (GT)26; Cob Swamp, Belize (BZ)24; Rio Hondo Delta25; Caye Coco, BZ23; and Lake Yojoa, Honduras (HN)27, together with summed probability distribution of the earliest maize cobs (n = 11) in southeastern Mesoamerica from El Gigante rock-shelter, HN28. Also shown in yellow is the known transition to staple maize agriculture based on dietary stable isotope dietary data from MHCP and ST8.
Published: 22 March 2022 South-to-north migration preceded the advent of intensive farming in the Maya region
Abstract The genetic prehistory of human populations in Central America is largely unexplored leaving an important gap in our knowledge of the global expansion of humans. We report genome-wide ancient DNA data for a transect of twenty individuals from two Belize rock-shelters dating between 9,600-3,700 calibrated radiocarbon years before present (cal. BP). The oldest individuals (9,600-7,300 cal. BP) descend from an Early Holocene Native American lineage with only distant relatedness to present-day Mesoamericans, including Mayan-speaking populations. After ~5,600 cal. BP a previously unknown human dispersal from the south made a major demographic impact on the region, contributing more than 50% of the ancestry of all later individuals. This new ancestry derived from a source related to present-day Chibchan speakers living from Costa Rica to Colombia. Its arrival corresponds to the first clear evidence for forest clearing and maize horticulture in what later became the Maya region.
Previous ancient DNA analyses have indicated that the earliest Central and South Americans, as well as present-day groups from the same regions, descend primarily from the more southerly of two founding Native American genetic lineages1,2,3,4,5. Published early Holocene (9400–7300 cal. BP) individuals from Belize (N = 3) are consistent in deriving their ancestry from this same large-scale north-to-south movement of people, but they display only distant relatedness to present-day groups in Mexico and Central America, including local Maya-speaking populations2. Instead, Maya people today show the greatest affinities to both South Americans and Indigenous Mexicans6,7, suggesting the potential for further episodes of population movement and admixture in this region during the past 7300 years. The genetic history of the region is essential to understand the evolution of cultures, languages, and technologies, including domesticated plant crops that transformed the neotropics.
Additional evidence of admixture is provided by substantial matrilineal discontinuity between the 9600-7300 cal. BP and 5600–3700 cal. BP groups. The majority of the 9600–7300 cal. BP individuals (5 of 6, in addition to a low-coverage individual from ~7000 cal. BP) carried mtDNA haplogroup D (including D4h3a and D4h3a5 haplotypes rare in the region today), and the sixth carried haplogroup C1b. By 5600–3700 cal. BP, however, the matrilineal makeup of the sampled individuals was almost entirely different, dominated by haplogroups C1c (9 out of 15) and A2 (5 of 15), similar to distributions found broadly in Central America today47,48. Although changes in uniparental genotype frequencies can sometimes be driven by random genetic drift, the almost entirely different sets of mtDNA haplogroups observed between the two time periods are consistent with the evidence of population transformation between the 9600–7300 cal. BP and 5600–3700 cal. BP groups based on the genome-wide data.
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quote: The 2015 DNA studies revealed Australasian ancestry in two Indigenous Amazonian groups, the Karitiana and Suruí, based on the DNA of more than 200 living and ancient people. Many bore a signature set of genetic mutations, named the "Y signal" after the Brazilian Tupi word for "ancestor," ypikuéra. Some scientists speculated the Y signal was already present in some of the earliest South American migrants. Others suggested a later migration of people related to present-day Australasians could have introduced the Y signal into people already living in the Amazon.
The new study, led by geneticist Tábita Hünemeier at the University of São Paulo, São Paulo, examined genetic data from 383 modern people from across South America, including dozens of newly genotyped individuals living in the Brazilian Amazon and central plateau. The researchers worked closely with Indigenous people, and Hünemeier says they are collaborating with historians, anthropologists, and geneticists "to assure the results would be transferred in the best way to the Indigenous communities."
For the first time, scientists identified the Y signal in groups living outside the Amazon—in the Xavánte, who live on the Brazilian plateau in the country's center, and in Peru's Chotuna people, who descend from the Mochica civilization that occupied that country's coast from about 100 C.E. to 800 C.E.
Next, the researchers used software to test different scenarios that might have led to the current DNA dispersal. The best fit scenario involves some of the very earliest—possibly even the earliest—South American migrants carrying the Y signal with them, the researchers report today in the Proceedings of the National Academy of Sciences. Those migrants likely followed a coastal route, Hünemeier says, then split off into the central plateau and Amazon sometime between 15,000 and 8000 years ago. "[The data] match exactly what you'd predict if that were the case," Raff agrees.
David Meltzer, an archaeologist at Southern Methodist University who co-authored the 2015 study identifying the Y signal, says that explanation makes sense. Still, he adds, finding Australasian ancestry in ancient coastal remains would boost his confidence in the authors' conclusions.
Pontus Skoglund, a population geneticist at the Francis Crick Institute who was a co-author on one of the 2015 studies with Hünemeier, says he's glad to see South American scientists building on the previous work. "I'm excited that local research groups in Brazil are picking this up. They're doing exactly what needed to be done."
One unanswered question is why the Y signal hasn't turned up in any North or Central American Indigenous groups. One possibility, Hünemeier suggests, is that the Y signal–bearing migrants simply stuck to the coast and made it to South America without leaving any genetic legacy up north. It's also possible that groups with Y ancestry did live in North and Central America, but died out in the deadly aftermath of European colonization. "The population Y signal is a puzzle," Meltzer says, "but this is an interesting piece to add to it."
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A new book by anthropologist and geneticist Jennifer Raff adresses several of the questions regarding the peopling of the Americas. The book is recently published so I have not had time to read it yet, but it seems interesting. A shorter article on the same theme can be read in Scientific American, May 2021
Genomes Reveal Humanity's Journey into the Americas
Origin: A Genetic History of the Americas . by Jennifer Raff. Published by Twelve Books, 2022.
Dr Jennifer Raff is interviewed in the podcast Tales from Aztlantis:
Peopling the Americas w/ Dr. Jennifer Raff!
quote: Today we are joined by geneticist Dr. Jennifer Raff to talk about genetic research, what it can tell us about the peopling of the Americas, and how it can be misused by pseudohistorians and psudoarchaeologists to promote dangerous misinterpretations of the past!
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