Gene-mapping a continent

DNA: A researcher from Maryland crisscrosses Africa drawing blood samples that shed light on the earliest human history.

Medicine & Science

April 12, 2004|By David Kohn | David Kohn,SUN STAFF

These days, most scientists don't worry about being denounced as witches, vampires or body snatchers.

Sarah Tishkoff is an exception. In the course of her DNA research travels around Africa, she has been accused of these offenses and more. One tribe in Tanzania refused to let her into their village.

"They thought that white people were coming to steal their children, or to kill them, or to take their body parts or their blood," Tishkoff recalled. "And I did want to take their blood. So, then it's really scary."

Over the past seven years, Tishkoff, a genetic anthropologist at the University of Maryland, has drawn a lot of blood: more than 3,000 samples from more than 50 African ethnic groups across the continent, from Pygmies in Cameroon to the Masai in Tanzania.

Her goal is to harvest DNA from the red blood cells and create genetic maps that reveal the outlines of our earliest history. Colleagues say Tishkoff's research is transforming the study of human origins.

"She's really cutting-edge," said George Washington University anthropologist Alison Brooks, who has spent more than three decades studying African prehistory. "There are all these people collecting genes in Finland and India, but no one was really working in Africa. We know very, very little about the African gene pool."

Tishkoff is convinced African genes hold the key: "If I want to know deep human origins, I only need to look in Africa."

Sitting in her small office on the College Park campus, Tishkoff, 37, doesn't look like a scientific adventurer. With her loose, shoulder-length brown hair and round face, she lacks the flinty intensity of primate research stars Jane Goodall or Dian Fossey (or at least Sigourney Weaver playing Dian Fossey).

But make no mistake: Tishkoff, who lives in Ellicott City with her husband and 7-month-old daughter, takes serious risks for her samples.

In northeast Tanzania, she found herself working in the midst of an outbreak of plague. Elsewhere in that country, she and her assistants were set upon by tsetse flies, which carry sleeping sickness -- a painful and potentially fatal disease. In both cases, she escaped infection.

Other hazards include bad drivers and barely passable roads, which combine to cause frequent accidents -- often lethal, given the dearth of hospitals. In Tanzania, her Land Rover was hit head-on by a bus rounding a curve. Luckily, no one was hurt.

The work is grueling. On expeditions, Tishkoff typically wakes at 7 a.m., works all day, takes a dinner break and then processes the day's samples until 11 p.m. or midnight.

Handling the blood poses its own dangers. Removing DNA from red cells is messy work, and in some regions, as many as a third of the inhabitants have HIV. To protect herself, Tishkoff wears goggles, gloves, and long pants and sleeves.

"She has chutzpah," said Brooks. "If she wants something, nothing stands in her way."

Tishkoff has overcome other obstacles. African officials are often wary of gene researchers, suspecting them of molecular colonialism -- using African DNA to discover lucrative drugs. To persuade skeptics of her honorable intentions, Tishkoff forms partnerships with African researchers and provides basic medical care to villages she visits.

As for concerns about witchcraft, she works closely with local officials and village chiefs, relying on them to explain why she wants blood. Eventually, most villagers grasp the basic outlines of her work and wind up being sympathetic and curious, she says.

Tishkoff first focused on African DNA as a genetics grad student at Yale. She discovered that this particular gene pool was barely known and that studying it would allow her to combine her interests in history, anthropology and genetics. (Her own genes might have played a role in this choice: Her mother is a history professor; her father is a hematologist.)

Until Tishkoff began her expeditions, researchers who wanted to study African DNA generally used samples from two Pygmy groups, assuming they were genetically representative of the continent. It turned out that these tribes were isolated and inbred, and their DNA was quite different from most other Africans.

In fact, Tishkoff says, there is no such thing as an "average" African. Because humans have been there for so long -- at least 150,000 years, most researchers say -- the continent has more genetic variety than the rest of the world combined.

"We find more diversity between two African groups than between an African and an Asian, or a European and a Papua New Guinean," she said.

Tishkoff sees this genetic variety as an extraordinary window into mankind's beginnings. Over thousands of years, genes undergo mutation, changing at a relatively steady pace. Researchers use this mutation rate as a kind of clock -- by comparing genetic information from different ethnic groups, they can create a rough family tree for early human populations and track their migrations.

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