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Geneticists have created a detailed map of how humans spread from their
home base in sub-Saharan Africa to populate the farthest reaches of the
globe over the last 100,000 years.
The researchers scrutinized the DNA of 938 people from 51 distinct
populations around the world. And the pattern of genetic mutations, to
be published today in the journal Science,
offers striking evidence that an ancient band of explorers left what is
now Ethiopia and — along with their descendants — went on to colonize
North Africa, the Middle East, Europe, southern and central Asia,
Australia and its surrounding islands, the Americas and East Asia.
A second analysis based on some of the same DNA samples corroborated
the results. Those findings, published Thursday in the journal Nature,
demonstrated that the greater the geographic distance between a
population and its African ancestors, the more changes had accumulated
in its genes.]
The story of human migration revealed by DNA "complements what's known
through history, linguistics or anthropology," said Jun Li, the
University of Michigan human geneticist who led the Science study.
Both research groups relied on DNA from blood samples collected by
anthropologists around the world as part of the Human Genome Diversity
Project, a controversial effort from the mid-1990s to gather genetic
specimens from thousands of populations, including many indigenous
tribes.
Previous studies have relied on data from the International HapMap
Consortium, which cataloged DNA from 269 people of Nigerian, Japanese,
Chinese and European descent.
"Instead of saying a particular person's genome is from Africa,
this kind of data allows us to say which part of Africa they were
from," said Andrew Singleton, chief of the molecular genetics section
at the National Institute on Aging in Bethesda, Md., and senior author
of the Nature report.
In both studies, the researchers analyzed more than a half-million
single-letter changes among the approximately 3 billion As, Cs, Ts and
Gs that make up the human genome.
Those changes — called "single nucleotide polymorphisms," or SNPs —
begin as random mutations and accumulate over time as they are passed
from one generation to the next.
Each time a small group left its home territory to found a new
population, the migration ultimately led to a unique pattern of SNPs.
Comparing those patterns, the researchers were able to show that humans
spread around the globe through a series of migrations that originated
from a single location near Addis Ababa, Ethiopia.
With the expanded DNA data set, Li's group was able to make finer
distinctions among groups that were previously treated as homogeneous
populations.
By creating a catalog of normal genetic variability among different
groups of people, the studies will help medical researchers pinpoint
the role of genes in specific diseases, said Singleton, whose lab is
part of the National Institutes of Health.
The Los Angeles Times is a Tribune Co. newspaper.
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