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8-Humans: US scientists plan to screen Africans' genomes

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TITLE:  Analyzing Africa's abundant gene pool
SOURCE:, USA, by Robert Cooke
DATE:   October 30, 2001

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Analyzing Africa's Abundant Gene Pool

San Diego - GENETICISTS hoping to trace the human species all the way back 
to its evolutionary roots are mounting a campaign to find, identify and 
analyze genes from all of Africa's many populations.

A genetic survey of Africans would be valuable because the variation in 
genes seen in Africa far outpaces the diversity seen anywhere else in the 
world. And Africans represent the foundation - the very ground from which 
all modern people arose.

The idea for a survey of African genes arose among geneticists a year ago, 
and momentum accelerated recently here at the annual meeting of the 
American Society of Human Genetics. Specialists in population genetics and 
evolution analyzed what it would take to explore the genetic backgrounds of 
Africa's many distinct population groups.

They'll also be digging into the inherited diseases that still afflict 
humanity, many of which originated deep in the past, when Homo sapiens was 
still confined to Africa. Many infectious diseases also began afflicting 
humans before they ever left Africa, and studying their interactions with 
genes will be useful.

As a topic for scientific study, Africa "is very important, but under-
represented, in the field of human genetics," said geneticist Sarah 
Tishkoff of the University of Maryland. And because Africa was the original 
home for modern humans, it's the obvious place to go in search of genetic 

In addition, she said, the information gleaned from genetic studies in 
Africa will be interesting for millions of African-Americans anxious to 
learn of their own history and origins - which can be challenging in cases 
where ancestors were uprooted and dispersed by slavery.

Geneticist Douglas Wallace of Emory University in Atlanta pointed out that 
"Africa had been the home of our hominid ancestors for millions of years," 
so Africa must be the source from which "our most recent ancestors migrated 

"The genes show that," Wallace said, in that most of the variation seen 
among human genes is visible among the African populations. In contrast, 
Asians are more like each other, and Europeans - the latest migrants - show 
even less variation among themselves.

So the conclusion is that "Africa was populated by humans the longest, 
followed by Asia and then Europe," Wallace said.

After years of argument, it is generally accepted among scientists that the 
most modern version of humanity, Homo sapiens, evolved and developed in 
Africa. Fossils suggest that the latest part of evolution probably occurred 
in eastern Africa, before people migrated out into Asia and Europe about 
65,000 years ago. These were the migrants who spread out until they 
populated the entire world.

What the migrants left behind in Africa, scientists now realize, were 
people who themselves evolved further into many, many distinct population 
groups and settled in western, eastern and southern Africa. In fact, the 
study of languages shows that almost one third of all the world's languages 
are spoken in Africa. As noted by Tishkoff, "there are 2,000 languages in 
Africa, 200 in Nigeria alone, so there is a lot of diversity" on the 
African continent.

And if the genetic variation matches linguistic patterns, there should be a 
treasure trove of genetic diversity awaiting close study.

"It is no surprise that there is a lot of genetic diversity" there, 
Tishkoff explained, because Homo sapiens has been there for more than 
100,000 years.

Still, in spite of the importance of evolutionary data, "Africa remains one 
of the least-studied areas in terms of genetic diversity," she said. Now, 
Tishkoff, Wallace and dozens of other researchers - including African 
researchers - hope to correct the imbalance. Tishkoff, for example, is 
pursuing research among several population groups in the southeastern 
nation of Tanzania. She and her colleagues have already found that genetic 
differences between various tribal groups are huge. It's clear, she said, 
that "there's almost as much genetic diversity in Africa as there is in all 
the rest of the world."

The genetic researchers repeatedly emphasized, however, that scientists 
must take extraordinary care to treat local African people with respect 
during genetic studies. She recalled that one tribe in northern Tanzania is 
still waiting, after half a century, for scientists to return with the data 
they'd promised.

Tishkoff advised that every time scientists propose to do research on a 
group, there should be a village meeting where the scientists "explain the 
project and answer questions from the people. We have to avoid 'hit-and-run 
genetics.' The Africans must be involved, and they must benefit from this 

Asked by a member of the audience what benefits the Africans might get from 
such work, Tishkoff replied that "we've tried to offer information about 
their ancestry, which fits with their concept of ancestry through blood." 
The scientists also share what they learn about diseases, "and their 
population's history; they really want to know about their history" as a 
distinct people.

Wallace added that his own team's research, which has focused on Ethiopia, 
found that the migration from Africa into Asia occurred about 50,000 years 
ago, while the exit into Europe came 40,000 years ago. He added that the 
genes representative of the people who left Ethiopia heading for Asia and 
Europe are still detectable in members of a tribe living in a very remote 
part of southern Ethiopia.

"We can see the lineages that we find in Europe" today, Wallace said, so 
the evidence suggests the migrations out of Africa began in what is now 


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