The great WALKABOUT

The findings—the latest dividend from the world’s investment in the Human Genome Project—confirms a broad narrative of human history known from previous biological, archaeological and linguistic studies. But the new research adds an astonishing level of detail, and a few new insights, that were not previously available.
All three studies support the idea that modern human beings left East Africa, walked into Central Asia and then fanned out east and west to people the entire planet. They also confirm earlier research showing that as a group, Africans have more diverse genes than people of other continents.

But the new research also shows that genetic diversity declines steadily the farther one’s ancestors travelled from Addis Ababa, Ethiopia, which is roughly the site of the exit turnstile for the “out-of-Africa” migration.
The studies also show that many seemingly “purebred” ethnic groups have ancestry traceable to more than one continent. For example, the Arabian Peninsula’s Bedouin—a culturally distinct grouup—are descended not only from long-time Middle Eastern peoples, but also from Europeans and peoples originating from around modern Pakistan. The Yakut people of eastern Siberia share blood with East Asians, Europeans and American Indians, but very little with Central Asians.

The biggest message, though, is that these differences are the details, not the main message, of human diversity. About 90 percent of the full catalogue of human genetic diversity exists in every human population. Individuals are likely to have almost as many differences with people we consider to be “like us” as with strangers on the other side of the world.

“What this says is that we are all extremely related to each other,” said Richard Myers, a geneticist at Stanford University School of Medicine, who helped lead one of the studies in the journal Science. “Most genetic variation is shared worldwide. It is only a small part of human genetic variation that is private to particular continents,” said Noah Rosenberg, of the University of Michigan. His group’s findings were published in the journal Nature.

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