Mutation studies shed light on human history

Mutation studies shed light on human history

Washington Post

WASHINGTON — We’re all pretty much the same except, of course, for the little things that make us different.

Those are the conclusions of three studies published last week that looked at human diversity through the keyhole of the genetic mutations we all carry.

The findings — the latest dividend from the world’s investment in the Human Genome Project in the 1990s — 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 traveled 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 group — 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, who are geographically closer to them than two of those populations.

The research may also shed light on the genetic underpinnings of human disease. One study found that Americans of European descent carry a larger number of damaging gene variants than blacks do — a byproduct of Caucasians’ arduous march eastward to the shores of the Atlantic.

The biggest message, though, is that these differences are the details, not the main message, of human diversity.

About 90 percent of the full catalog 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, published in Science.