1 ANCIENT AND MODERN DNA IN THE AMERICAS: IMPLICATIONS FOR THE PEOPLING OF THE NEW WORLD Frederika...

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ANCIENT AND MODERN DNA IN THE AMERICAS:

IMPLICATIONS FOR THE PEOPLING OF THE NEW

WORLD

Frederika A. Kaestle, Ripan S. Malhi, Jason A. Eshleman, David Glenn Smith

PAMinSA, Rio de Janeiro, July 27, 2005

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Detecting Population Continuity

• We often wonder how ancient populations are related to living populations

• Very difficult to assess, especially over long periods of time

• Culture changes, languages change, even anatomy changes

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Peopling of the Americas

• From Where?

• When?

• Are Modern Indians the descendants of the

first inhabitants?

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Mitochondrial DNA (mtDNA) Evidence• Analysis of mtDNA shows that modern Native Americans

belong to one of five mtDNA haplogroups (maternal lineages defined by shared mutations which were inherited from a common maternal ancestor)

• Called A, B, C, D and more recently discovered X

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MtDNA Evidence

• Four of these haplogroups are also widespread in Asia (although at low frequencies), with the fifth present in low frequencies in Western Asia, supporting the hypothesis that Native Americans are descendants of Asians who migrated across the Bering Land Bridge (or along the coast of it) from Siberia to Alaska

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MtDNA Haplogroup Frequencies

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MtDNA Haplogroup Frequencies in Asia• Various populations within Asia have been suggested as

most closely related to Native Americans

• Several studies have supported the hypothesis that Mongolian/Lake Baikal populations possess the highest frequency of A, B, C, and D in Asia, and might therefore be the best candidates

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Source Population?

Kolman, Sambuughin & Bermingham (1996) Genet. 142:1321-34

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Haplogroup X?• Haplogroup X, found in varying frequencies among

modern Native Americans, is more problematic -- so far it’s only been found in Europe, the Middle East, and Western Asia, always in quite low frequencies

• This has led some to suggest that there was some European contribution to the early peopling of the Americas (either through Asia or across the North Atlantic)

http://clovisandbeyond.org/

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Haplogroup X?• But it is also possible that haplogroup X was present in the

ancestral Asian population (perhaps Mongolia -- in fact, today it is found among the Altai, who live just West of Mongolia) but has since been lost due to genetic drift

• Y chromosome lineages found among Native Americans (1C and 1F) are also found at high frequency in the Lake Baikal/Mongolia region

• However, recent research suggests that the X lineages found in the Americas are members of a distinct sublineage not found in the Old World, and predate the origin of the sublineage found in the Altai.

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Haplogroups in Americas

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How Many Migrations• Although several geneticists have argued for evidence of multiple

migrations, we believe current mitochondrial evidence supports a single migration

• Cannot use the level of diversity within each haplogroup to date their origin or age, because differing population histories and sampling, as well as hypervariability leading to reticulation in gene trees also affect these estimates.

• The presence throughout the Americas of all 5 matrilines, combined with the low frequency of these matrilines in Asians, argues for a single migration (it would be unexpected to sample these same 5 rare lineages in multiple, independent migrations from Asia).

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How Many Migrations

• Y Chromosome data provides an independent view on this issue.

• Y lineages C and Q are the major lineages found among Native Americans, distributed throughout the Americas.

• These lineages are rare or absent elsewhere, except in northern Asia where they are relatively common (~25%).

• Again, this supports a single migration into the Americas

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When?• Due to the objections already mentioned, dating the

timing of the expansion of the mtDNA and Y chromosome lineages into the Americas is extremely problematic

• Previous estimates (generally flawed) have suggested a date of 15-20kyBP.

• However, recent reanalysis of genetic data from multiple loci utilizing a Bayesian “Isolation with Migration” model (Hey 2005) suggests a more recent origin of 7-15kyBP. May still be flawed.

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PaleoIndians• Earliest humans in the Americas

• Anatomical features appear to be distinct from those found among modern Native Americans

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Northern PaleoIndians• Quantitative analyses are consistent with this conclusion

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Southern PaleoIndians• Quantitative analyses are consistent with this conclusion

(Lapa Vermelha IV, Luzia)

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Population Continuity?• These differences have led some to suggest that

the earliest inhabitants of the Americas are NOT the direct ancestors of modern Native Americans

• The implication is that they do not have living descendants, and were replaced by later migrations into the Americas

• So, what mitochondrial lineages do we find among these paleoindians?

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Preliminary PaleoIndian ResultsSample N C14 (Uncorr) results Source

Arlington Springs, Santa Rosa Is., CA 1 9300 B Kaestle & Smith LabsBrowns Valley, MN 2 9049 D Kaestle & Smith LabsCutler Sink, Miami, FL 3 9620 B Kaestle & Smith LabsHorn Shelter, Waco, TX 2 9500-10300 B Kaestle & Smith LabsPelican Rapids, MN 1 7840 C Kaestle & Smith LabsOn Your Knees Cave, Alaska 1 10300 D Kemp et al 2005Windover, FL >60 7400 X, ? (N=12) Smith et al 1999, Hauswirth 1994Wizards Beach, Pyramid Lake, NV 1 9200 C Kaestle 1998Snake River, WA 1 8500 * Kaestle & Smith LabsHourglass Cave, CO 1 8000 B Stone & Stoneking 1996Kennewick, WA 1 8410 * Kaestle, Smith & Merriwether Labs

* = no analyzable DNA recovered

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Continuity• All of the Paleoindians we have been able to type belong

to one of the mitochondrial lineages present in living Native Americans

• For those identified by haplotype-specific sequence information, identical haplotypes are found among living Native Americans

• This suggests that there has been genetic continuity between these earliest PaleoIndians and modern Native Americans, despite the morphological differences between them

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Conclusions• Genetic Evidence supports a single

migration, from East Central Asia, with a small founder population leading to low genetic diversity

• Dating this is difficult, but recent estimates are younger than previous ones

• There appears to be genetic continuity between PaleoIndians and modern Native Americans

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Acknowledgements• Thanks to:

– All Individuals who gave permission for their DNA to be sampled, or for ancient DNA analyses

– Many Current and Former Members of the Smith and Kaestle Labs

• Including Deborah Bolnick, Brian Kemp, Joseph Lorenz, Phil Morin, Holly Mortensen, Jennifer Raff, Beth Shook, Joy Viray,

– Funding from NSF, NIH, UC Davis, Yale University– Our colleagues for stimulating conversation on relevant (and

irrelevant) topics, and important aid in obtaining samples.