Presentation on theme: "1 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."— Presentation transcript:
1 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
2 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
3 Peopling of the Americas From Where? When? Are Modern Indians the descendants of the first inhabitants?
4 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
5 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
7 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
9 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/
10 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.
12 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).
13 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
14 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.
15 PaleoIndians Earliest humans in the Americas Anatomical features appear to be distinct from those found among modern Native Americans
16 Northern PaleoIndians Quantitative analyses are consistent with this conclusion
17 Southern PaleoIndians Quantitative analyses are consistent with this conclusion (Lapa Vermelha IV, Luzia)
18 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?
20 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
21 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
22 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.