Tracing human diversity through the ages
STANFORD SCIENTISTS FIND SURPRISING LINKS
By Lisa M. Krieger
Article Launched: 02/22/2008 01:35:17 AM PST
A coalition of Stanford scientists has released the most detailed road map yet of human diversity, offering insight into the emergence and restless migration of the world’s populations.
Using the Stanford Human Genome Center to study genetic variations in almost 1,000 individuals from 51 populations, the team has completed the largest analysis to date of human diversity. The data is published in today’s issue of the journal Science.
The scientists discerned some of the great sweeps of human movement, like the early exodus out of Africa. They also found evidence of more recent micro-migrations by groups like American Indians, Silk Route traders and the Mongol invasion led by Genghis Khan.
“This is the definitive study to show variation within populations,” said Marcus Feldman, professor of biological sciences and a member of the team.
“During the long historical migrations, people have left genes along the way,” said Feldman, who has spent decades studying human genetic diversity, along with co-author Luca Cavalli-Sforza, a professor emeritus of genetics.
They grouped people according to their similarities at 650,000 locations on their DNA – a far higher level of precision than in previous studies.
“We were able to get a picture of the genetic differences and similarities in these people in much greater detail than before,” said senior author Richard Myers, professor of genetics.
For instance, the team found that:
â€¢ Political separatist groups, such as the Basques, Sardinians and the Adygey from the north Caucasus Mountains of Russia, are genetically distinct – not just culturally and politically different – from their surrounding populations.
â€¢ A group of Russian people called the Yakuts, native to the cold, dry tundra of Siberia, share genetic similarities with people indigenous to South and Central America – such as the Mayans, the Pima and even the Surui of the Brazilian jungles. This supports theories about human migration from Siberia across the Bering Strait to the Americas.
â€¢ Chinese fall into northern and southern groups. People who live along the northern border near Mongolia are genetically distinct from the Han Chinese of the southern part of the nation.
â€¢ Middle Eastern populations show multiple sources of ancestry.
For example, the largely Pakistani populations of Burusho, Pashtuns and Sindhi can trace their genetic roots to East Asia. The Palestinians, Bedouin and Druze carry genes also found in Europe and South/Central Asia.
“This tells us that the Middle East has long been a center of migration – that people have been passing through there and leaving genes as they go, either from east or from the west,” Feldman said.
The marauding Mongols left not just a huge cultural and historical impression in central Asia, but also a genetic one. For instance, the Hazara people of central Afghanistan share genetic ties with East Asia.
Silk Route traders left their own mark. The Uighur, a Muslim minority in northwest China, share genes with people in Europe and west Asia.
The data also bolsters the prevalent “Out of Africa” theory that humans emerged from the sub-Sahara, perhaps Ethiopia or Tanzania, then colonized the world in several waves.
The Stanford work is based on the fact that genetic material is rigidly passed down from parents to children. But along the way, there are errors, mostly harmless, called mutations, that arise when the DNA is erroneously copied during cell division. They occur at a constant rate.
Genome Center magnifying tools made it possible to study these very tiny genetic mutations, called polymorphisms. Mathematical analysis of the mutations – looking at differences and similarities between populations – creates a historical map of human migration.
In the future, they hope to have access to samples from even more populations, adding to the map.