In The Field

ASGH 2009: Problems of blood

Jibril Hirbo hails from a tiny mountaintop town called Marsabit, in northern Kenya. Now, as a population geneticist, Hirbo has completed perhaps the largest-ever genetic study of people from Kenya and other East African nations.

The study, he reported yesterday, examined 1,500 people from 66 ethnic groups in East Africa, roughly doubling the number of African populations studied to date. The study provides valuable data about human evolution. For instance, it strengthens the evidence that the “out of Africa” event, in which humans left the continent to colonize the rest of the world, occurred in East Africa sometime within the past 100,000 years. And the data will help clarify the migration and mixing events that connect Africa’s diverse ethnic groups.

Hirbo says, the results are especially interesting to people from his own ethnic group, the Burgee, a group of about 10,000, many of whom now live in southern Ethiopia. He remembers that as a child, people in his town started to suffer from increasing rates of diabetes and cancer, and they weren’t sure why. Some blamed it on witchcraft, or on caste, thinking that these were diseases of the lower classes. But then, respected members of the community started dying from these same diseases. So the caste explanation couldn’t be right.

That’s what motivated Hirbo to become one of only two people from his primary school to go to college, and the only one to get a doctoral degree. At first, he wanted to become a medical doctor, to try to understand the reason behind the illnesses that plagued his neighbors. But along the way, his goals changed. He wanted to understand the genetic variation that might predispose some to disease and grant others immunity. He is now a graduate student working with Sarah Tishkoff of the University of Pennsylvania in Philadelphia.

African genetics have not been nearly as well studied as genetics of Europeans and other western populations. But the few studies that have been done so far, such as Hirbo’s, confirm that Africa harbors more genetic diversity than Europe, because humanity’s original genetic diversity was slowly lost as humans migrated away from Africa to colonize the rest of the world.

Tishkoff says that population studies like Hirbo’s are important for understanding both human history and genetic characteristics that might affect people’s propensity to get disease and respond to drug treatments. And the Africans who participate in the studies hope to learn something about their own histories, Hirbo says.

For that reason, Hirbo and Tishkoff both have plans to travel back to Africa to share what they have found. “I grew up in a small village where people narrate oral traditions and myths about their origins, and so when you tell people you want to know about the traditions based on blood, that’s what they understand, and they really get excited about the results,” Hirbo says.

And it’s no longer true that Hirbo’s old friends and neighbors in Marsabit believe that disease is a result of witchcraft. Now they know, Hirbo says, that disease is “a problem of blood.”


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