8-Humans: US scientists plan to screen Africans' genomes
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TITLE: Analyzing Africa's abundant gene pool
SOURCE: Newsday.com, USA, by Robert Cooke
DATE: October 30, 2001
------------------ archive: http://www.gene.ch/genet.html ------------------
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
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
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
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
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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