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||Re: Patterns of genetic diversity
« Reply #1 on: Dec 16th, 2008, 6:12pm »
…The research demonstrates that both immigration events from the Middle East and North Africa over the last two millennia and introduction of new Y-chromosome types driven by religious conversion and intermarriage have had a dramatic impact on modern populations in Spain, Portugal, and the Balearic Islands.
In addition, the findings indicate that recent history should be considered when investigating the impact of events occurring during the earlier prehistory of Europe. The research was funded by the Wellcome Trust.
Most native tribes who live and lived within Brazil’s current borders are thought to descend from the first wave of migrants from North Asia (Siberia) that crossed the Bering Land Bridge at the end of the last Ice Age around 9000 BC. In 1500 AD, the territory of modern Brazil had an estimated total population of nearly 3 million Amerindians divided in 2,000 nations and tribes.
A new study published November 26, 2007 (see Public Library of Science Genetics), which was led by University of Michigan and University College London researchers, seems to suggest that the Bering land bridge migration occurred during one specific time period, 12,000 years ago, that every human who migrated across the land bridge came from Eastern Siberia during that time period, and that every Native American is directly descended from that same group of Eastern Siberian migrants.
The claim suggests that a “unique genetic variant widespread in natives across both continents — suggesting that the first humans in the Americas came in a single migration or multiple waves from a single source, not in waves of migrations from different sources”.
Biogeographical evidence demonstrates previous connections between North America and Asia. Similar dinosaur fossils have been found between Asia and North America. For instance the dinosaur Saurolophus was found in both Mongolia and western North America. Relatives of Troodon, Triceratops, and even Tyrannosaurus rex all came from Asia.
In the complex history of human migrations, it is widely accepted that the New World continents were the ones colonized most recently by Homo sapiens, most likely from Asia through Beringia.
A popular model for the peopling of the Americas suggests that the archaeological remains known as the Clovis complex (thought to be the oldest unequivocal evidence of humans in the Americas) represent the people that first colonized the continent after a late glacial
migration through the ice-free corridor that separated the Laurentide and Cordilleran ice sheets.
However, the recently re-evaluated age of the Clovis sites to only between about 12.7 and 13.2 thousand years ago (kya)2 and the confirmed human presence at the Monte Verde site located in southern South America around 14.5 (kya)3 challenge this Clovis-first model and call for alternative hypotheses.
(Note, KYA is an acronym used by geologists and paleontologists for “1,000 years Ago”).
* TYA: Thousand years ago
* BYA: Billion Years Ago (109 years)
* MYA: Million Years Ago (3 MY = 3,000 years)
* kYA: kiloYears Ago (1 kY = 1,000 years)
* GYA: GigaYears Ago (1 GY = 109 years)
Since the first studies, it has been found that extant Native American populations exhibit almost exclusively five mtDNA haplogroups (A–D and X)6 classified in the autochthonous haplogroups A2, B2, C1, D1, and X2a. Haplogroups A–D are found all over the New World and are frequent in Asia, supporting a northeastern Asian origin of these lineages.
Mitochondrial DNA analysis reveals diverse histories of tribal populations from India.
This distribution, together with the similar coalescence time for these haplogroups, was used to suggest a single-migration model. However, a different pattern of diversification and distribution of haplogroup B found in some studies led some authors to hypothesize that it could represent a later and separate migration from the joint arrival of haplogroups A, C, and D.
The history of haplogroup X is more elusive; it is presently found in the New World at a relatively low frequency and only in North America, it is rare in West Eurasians, and it is almost absent in Siberia.
Genetic Variation and Population Structure in Native Americans
The American Journal of Human Genetics 82, 583–592, March 2008 583