Post by Blu on Jan 17, 2005 12:36:38 GMT -5
Early research with human mitochondrial DNA showed that genetic patterns cluster by geographical regions and that relationships between populations — evolutionary trees — can be established from these patterns. Some of this research shows genetic relations between Native Americans and Asians, supporting the theory of Asian origin. Merriwether's work is in the same vein, using Native American mitochondrial DNA to shed light on the migration of humans to the New World. "Using these molecular genetic techniques," he says, "we're attempting to trace the ancient migratory routes and determine how long ago contemporary populations separated from each other."
The three waves of migration proposed by some researchers correspond to three main Native American language groups — Amerind, Nadene and Eskaleut. According to this theory, Amerind people arrived about 30,000 years ago, followed 20,000 years later by the Nadene and then the Eskaleuts, who came to Alaska and northern Canada within the last 7,000 years. Some earlier mitochondrial DNA research supports this theory. This work found that all Native Americans come from four genetic lineages, labeled A through D, and that, significantly, Amerinds have all four lineages, Nadene only A, and Eskaleuts A and D — suggesting different migrations at different times.
Distribution of Native American Populations: This map shows populations included in Andrew Merriwether's study of evolutionary relationships among Native Americans. Many populations (red dots) were not included in prior studies. Other data (black dots) reported in the literature was also analyzed along with the new populations. The underlined populations indicate burial sites where DNA was collected from teeth, bone fragments and mummified tissue.
Working with a much larger dataset than the earlier studies, Merriwether found that the four lineages divide into nine distinct genetic subtypes. Furthermore, directly challenging the three-wave theory, all four lineages showed up in all three language groups. "The key finding," says Merriwether, "is that many of the populations have all four lineages and a number even have all the subtypes. And all types can be found in North, Central and South America. It isn't realistic to believe that the same lineages ended up in all these populations across two continents by separate migrations."
Merriwether's DNA sample includes 1,300 Native Americans representing more than 40 populations throughout the Americas, along with 300 samples from teeth, bone fragments and mummified tissue at three burial sites, one each in North, Central and South America. By including a broader range of populations and large sample sizes, 50 to 100 individuals per population compared to 10 to 20 in other studies, this research offers the most reliable results yet tracing evolutionary relationships among Native Americans. The large data set also presents a demanding analytical task, which is where the CRAY C90 comes in. "When you look at thousands of individuals for long DNA sequences," says Merriwether, "you can't do it without the supercomputer. It makes problems feasible that weren't possible to address before. This methodology's been around awhile, but we didn't have the computing power. It's as simple as that."
As the dust settles and researchers in the field contemplate the likely demise of three-wave theory, Merriwether's team has taken up the task of building an evolutionary tree of the Yanomami Indians. This tribe, who live in the tropical rain forest between Brazil and Venezuela, were isolated from modern contact until the 1960s. Results from this unique living population, unmixed with post-Colombian influence, suggest at least three more genetic lineages for the original Native Americans.
www.psc.edu/science/Merri/merri.html
The three waves of migration proposed by some researchers correspond to three main Native American language groups — Amerind, Nadene and Eskaleut. According to this theory, Amerind people arrived about 30,000 years ago, followed 20,000 years later by the Nadene and then the Eskaleuts, who came to Alaska and northern Canada within the last 7,000 years. Some earlier mitochondrial DNA research supports this theory. This work found that all Native Americans come from four genetic lineages, labeled A through D, and that, significantly, Amerinds have all four lineages, Nadene only A, and Eskaleuts A and D — suggesting different migrations at different times.
Distribution of Native American Populations: This map shows populations included in Andrew Merriwether's study of evolutionary relationships among Native Americans. Many populations (red dots) were not included in prior studies. Other data (black dots) reported in the literature was also analyzed along with the new populations. The underlined populations indicate burial sites where DNA was collected from teeth, bone fragments and mummified tissue.
Working with a much larger dataset than the earlier studies, Merriwether found that the four lineages divide into nine distinct genetic subtypes. Furthermore, directly challenging the three-wave theory, all four lineages showed up in all three language groups. "The key finding," says Merriwether, "is that many of the populations have all four lineages and a number even have all the subtypes. And all types can be found in North, Central and South America. It isn't realistic to believe that the same lineages ended up in all these populations across two continents by separate migrations."
Merriwether's DNA sample includes 1,300 Native Americans representing more than 40 populations throughout the Americas, along with 300 samples from teeth, bone fragments and mummified tissue at three burial sites, one each in North, Central and South America. By including a broader range of populations and large sample sizes, 50 to 100 individuals per population compared to 10 to 20 in other studies, this research offers the most reliable results yet tracing evolutionary relationships among Native Americans. The large data set also presents a demanding analytical task, which is where the CRAY C90 comes in. "When you look at thousands of individuals for long DNA sequences," says Merriwether, "you can't do it without the supercomputer. It makes problems feasible that weren't possible to address before. This methodology's been around awhile, but we didn't have the computing power. It's as simple as that."
As the dust settles and researchers in the field contemplate the likely demise of three-wave theory, Merriwether's team has taken up the task of building an evolutionary tree of the Yanomami Indians. This tribe, who live in the tropical rain forest between Brazil and Venezuela, were isolated from modern contact until the 1960s. Results from this unique living population, unmixed with post-Colombian influence, suggest at least three more genetic lineages for the original Native Americans.
www.psc.edu/science/Merri/merri.html