NEWS OF THE WEEK
GENETICS
1470
On the move. Colored
arrows depict the increasing genetic diversification
of humans after they migrated
eastward along what is now India’s
coast and split into numerous genetically
distinct groups that moved across Southeast
Asia and migrated north into East Asia.
funded, and completed by an Asian consortium,” adds Edison Liu, executive director of
the Genome Institute of Singapore and one
of the consortium’s key organizers (Science,
3 December 2004, p. 1667).
Previous studies, mostly by researchers in
Europe and North America, relied on limited
numbers of samples from just a handful of
Asia’s ethnic populations. This local grassroots effort opened the door to larger numbers
of more-representative samples.
The job wasn’t always easy. About half of
the 288 Indonesian samples had been collected previously, primarily from the country’s
major population groups. But tapping into
subpopulations typically required numerous
visits to village elders to explain the project,
its objectives, and the concept of informed
consent, says consortium organizer Sangkot
Marzuki of the Eijkman Institute for Molecular Biology in Jakarta. One isolated group in
central Sulawesi agreed to participate only if
all of its 1000 members were given medical
checkups. “So we went back with a mobile
medical unit,” Marzuki says.
Researchers screened each sample for
more than 50,000 single-nucleotide polymorphisms (SNPs)—sites on chromosomes
where a single base can vary from one individual to another. The number of variations, or
haplotypes, indicates how closely related two
individuals are genetically.
Not surprisingly, the genetic groupings
strongly correlate with linguistic and geographic groupings. But the consortium also
found that genetic diversity markedly
11 DECEMBER 2009
VOL 326
SCIENCE
Published by AAAS
decreased going from south to north. In addition, most of the genetic variations found in
East Asian populations were also present in the
Southeast populations, indicating that the former likely derived from the latter. The authors
conclude that humans migrated along a coastal
route from the Mideast to Southeast Asia and
from there moved north, gradually adapting to
harsher climates.
Jin says their findings do not completely
rule out a northern route migration. There is
evidence of genetic links across the Eurasian
steppe. But Jin thinks these links result from
genes flowing back and forth along ancient
trade routes rather than moving in as part of a
large-scale migration. Macaulay says more
data from central Asia could “hammer another
hefty nail in the coffin of the [two-wave]
model.” Yet Rosenberg says the authors “leave
some room for other multiple-wave theories,”
specifically that several different migrations
across the southern route could account for the
distinct populations seen in New Guinea, Australia, and the Pacific Islands.
The consortium intends to address these
questions in a second project that Liu says
will be more ambitious geographically—
including, the consortium hopes, central
Asian and Pacific Island nations—and scientifically, analyzing far more genetic markers
to map diversity and to extend the work to
genomic medicine. With the experience
gained on the consortium’s first project, the
riddles of Asia’s diversity may yet be solved
by the unified efforts of Asian scientists.
www.sciencemag.org
–DENNIS NORMILE
CREDIT: L. JIN ET AL., SCIENCE
A massive effort to catalog genetic variation
among Asians has just weighed in on the peopling of that vast continent. As described on
page 1541, a 40-institution consortium has
concluded that Asia was initially settled by a
single wave of migration along the coast;
exactly when is still to be determined.
“It’s a fabulous data set,” says Vincent
Macaulay, a statistical geneticist at the University of Glasgow in the United Kingdom. The
evidence for the southern coastal route and
against a northern steppe route “seems very
strong,” he adds.
Anthropologists, ethnographers, and
linguists have long struggled to understand
the patchwork-quilt diversity of Asia.
Indonesia alone claims some 300 ethnic
groups; the Philippines has 180 native languages and dialects. Where did they all
come from? In recent years, geneticists
joined in, using genomic markers to divine
mig ration patter ns and relationships
among different ethnic groups.
These efforts produced two basic theories to
explain the initial peopling of the continent.
The dominant one pictures two major waves of
migration from the Middle East. One wave followed a southern coastal route, around the rim
of present-day India, and continued from island
to island across Indonesia, Malaysia, and the
Philippines to the Pacific; a separate and distinct wave of immigrants traveled east across
the Eurasian steppe and turned south through
the Asian mainland. A second theory posits just
one initial migration—along the coastal
route—with populations moving north into
East Asia from there.
This new analysis by the HUGO Pan-Asian
SNP Consortium “strongly concludes the
southern route made a more important contribution to East and Southeast Asian populations
than the northern route,” says Li Jin, a population geneticist at Fudan University in Shanghai,
China, and one of the paper’s lead authors.
The results are significant for two other reasons. Scientifically, with samples from more
than 1900 individuals representing 73 populations, “this is the most comprehensive study of
genetic variation to date in East and Southeast
Asia,” says Noah Rosenberg, a bioinformaticist
at the University of Michigan, Ann Arbor,
who was not part of the consortium. Secondly,
the consortium comprises 93 researchers at
40 institutions in 11 countries and regions in
Asia, marking this a coming-of-age for the continent’s genomic sciences. This project “was
conceived by Asians in Asia and executed,
Downloaded from www.sciencemag.org on December 10, 2009
SNP Study Supports Southern Migration Route to Asia