Author: Brian Handwerk
Publication: National Geographic News
Date: January 10, 2006
URL: http://news.nationalgeographic.com/news/2006/01/0110_060110_india_genes.html?source=rss
Most modern Indians descended from South Asians,
not invading Central Asian steppe dwellers, a new genetic study reports.
The Indian subcontinent may have acquired
agricultural techniques and languages-but it absorbed few genes-from the west,
said Vijendra Kashyap, director of India's National Institute of Biologicals
in Noida.
The finding disputes a long-held theory that
a large invasion of central Asians, traveling through a northwest Indian corridor,
shaped the language, culture, and gene pool of many modern Indians within
the past 10,000 years.
That theory is bolstered by the presence of
Indo-European languages in India, the archaeological record, and historic
sources such as the Rig Veda, an early Indian religious text.
Some previous genetic studies have also supported
the concept.
But Kashyap's findings, published in the current
issue of the Proceedings of the National Academies of Science, stand at odds
with those results.
True Ancestors
Testing a sample of men from 32 tribal and
45 caste groups throughout India, Kashyap's team examined 936 Y chromosomes.
(The chromosome determines gender; males carry it, but women do not.)
The data reveal that the large majority of
modern Indians descended from South Asian ancestors who lived on the Indian
subcontinent before an influx of agricultural techniques from the north and
west arrived some 10,000 years ago.
Most geneticists believe that humans first
reached India via a coastal migration route perhaps 50,000 years ago.
Soon after leaving Africa, these early humans
are believed to have followed the coast through southern India and eventually
continued on to populate distant Australia.
Peter Underhill, a research scientist at the
Stanford University School of Medicine's department of genetics, says he harbors
no doubts that Indo-European speakers did move into India. But he agrees with
Kashyap that their genetic contribution appears small.
"It doesn't look like there was a massive
flow of genes that came in a few thousand years ago," he said. "Clearly
people came in to India and brought their culture, language, and some genes."
"But I think that the genetic impact
of those people was minor," he added. "You'd don't really see an
equivalent genetic replacement the way that you do with the language replacement."
Language, Genes Tell Different Tales
Kashyap and his colleagues say their findings
may explain the prevalence of Indo-European languages, such as Hindi and Bengali,
in northern India and their relative absence in the south.
"The fact the Indo-European speakers
are predominantly found in northern parts of the subcontinent may be because
they were in direct contact with the Indo-European migrants, where they could
have a stronger influence on the native populations to adopt their language
and other cultural entities," Kashyap said.
He argues that even wholesale language changes
can and do occur without genetic mixing of populations.
"It is generally assumed that language
is more strongly correlated to genetics, as compared to social status or geography,
because humans mostly do not tend to cross language boundaries while choosing
marriage partners," Kashyap said.
"Although few of the earlier studies
have shown that language is a good predictor of genetic affinity and that
Y chromosome is more strongly correlated with linguistic boundaries, it is
not always so," he added.
"Language can be acquired [and] has been
in cases of 'elite dominance,' where adoption of a language can be forced
but strong genetic differences remain [because of] the lack of admixture between
the dominant and the weak populations."
If steppe-dwelling Central Asians did lend
language and technology, but not many genes, to northern India, the region
may have changed far less over the centuries than previously believed.
"I think if you could get into a time
machine and visit northern India 10,000 years ago, you'd see people …
similar to the people there today," Underhill said. "They wouldn't
be similar to people from Bangalore [in the south]."
