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The Cleveland Plain-Dealer

In New, More Detailed DNA Tests, Geography Meets Genetics

Elizabeth Sullivan

For most of us, race is more than just skin color. It's also about ex perience and the context of one's life.

Amid all the condemnations and finger-pointing over the Rev. Jeremiah Wright's ill-chosen words and toxic rhetoric, that's actually the useful lesson he has to teach us. One does not have to embrace his words of blame and negation to understand they arise from a life, and the lives of forebears, that encompassed centuries of injustices rarely captured for history.

Yet far more binds than divides us in a world where history is written in the genes, and Barack Obama reportedly shares ancestry with both Dick Cheney and George W. Bush.

Human DNA is an unfolding map of the human expe rience, billions of "letters" and hun dreds of thousands of "words" that tell of tragic die-outs, great migrations, rapid adaptations, devastating military conquests - and, most importantly, the kinship of all who breathe.

Every person living today shares more than 99 percent of his or her genetic code.

And yet it is those tiny differences that tell the story of the last 200,000 years of human history - the time that has elapsed since a hypothesized genetic "Eve" lived in Africa.

She wasn't the real Eve or the first woman. Dating the genetic recoding for mitochondrial DNA, or mtDNA - the DNA that is passed virtually unchanged from mother to children - remains an inexact science.

Yet because of a mishap that befell the female descendants of all other women who predated her, this theoretical Eve became the likely progenitor of all of us.

It turns out such "bottlenecks" have happened more often than most of us realize. Soberingly often.

The word "bottleneck" sounds so innocent, yet it denotes huge die-outs of ancient peoples, whether from disease, war, weather or genocide. And the history of these horrors is written in our genes.

One such catastrophe may have winnowed the first peoples to settle the Americas. A new study suggests that most Native Americans alive today can trace their roots to just six founding "mothers" who survived a population collapse in Beringia - the now-submerged land bridge between Asia and Alaska - 20,000 years ago. The study was conducted by an international team including researchers at the Utah-based Sorenson Molecular Genealogy Foundation.

Other bottlenecks overtook ancient Europeans, with potential disease implications today.

A recent Cornell University study of nearly 40,000 genetic "letters" in 15 African-Americans and 20 European-Americans found in the European descendants the genetic slips and potentially damaging variations associated with such a bottleneck. That study was reported last month in the journal Nature.

Scientists theorize that such built-in genetic error codes tend to arise in cases where populations first crash and then explode based on a smaller gene pool and less eradication of bad DNA.

The prevalence of such catastrophes, as signaled by our DNA, is humbling. That is especially so given our deeper kinship as illustrated by a slew of recent studies heaping new evidence on the out-of-Africa theory of human migrations.

In one, scientists at Stanford University recently tested more than a half-million genetic "letters" in 51 population groups around the world. Published in the journal Science last month, results of the tests confirm the richer African genetic diversity of the "founders' " homeland, as well as its corollary: radiating bands of lessening genetic diversity the farther away from Africa people's origins progress.

Yet the Stanford study also suggests the dawning of a new age of genealogical discovery by showing the potential for a rich mining of genetic markers, thousands of times more detailed than most commercial genetic testing. The time may be coming when individuals will be able to pinpoint their origins with geographical precision, and learn in even greater detail how our shared family tree has both blossomed and faltered.

Elizabeth Sullivan is The Plain Dealer's foreign-affairs columnist and an associate editor of the editorial pages.

© 2008 The Cleveland Plain Dealer

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