Unravelling
mysteries of ancient human migrations
http://www.thehindu.com/thehindu/seta/2007/08/23/stories/2007082350011500.htm
Where
did humans originate and how did they populate the entire globe?
Scientists may finally be able to answer these fundamental questions
when they have enough DNA samples from people all over the world.
The
Genographic Project attempts to trace the ancient journey of man
through the genetic analysis of present-day populations on every
continent. This nonprofit, five-year research partnership of National
Geographic and IBM is led by geneticist Dr. Spencer Wells with
support from the Waitt Family Foundation.
India
is one of the ten international centres for this world-spanning
project. A state-of-the-art facility dedicated for genographic
work was established at the Madurai Kamaraj University this July.
Vijaysree Venkatraman interviewed Dr. Ramasamy Pitchappan, Regional
Director of Genographic Project, India. Excerpts:
How
will the work done in India help piece together the big puzzle?
Humans
have lived in India for 50,000 years at least. Ancient migrant
populations must have expanded in India for a long time giving
rise to various breeding isolates some of these tribes/castes
still practice endogamy.
Geneticist
Theodosius Dobzhansky once remarked: "The caste system in
India was the grandest genetic experiment ever performed on man."
The present study will unravel the mysteries of the origin, migration
and expansion of various populations under different climatic
conditions.
Tell
us about your involvement with the Genographic Project.
In
2000, when I was at Oxford, we carried out work to verify if the
first humans migrated via India to Australia. Fossils indicate
that Man lived in Africa and a fraction moved out 60,000 years
ago. Archaeological remnants were not found in any country en
route to Australia. So, how did our peripatetic ancestors get
there?
The
coastal marker M130 appeared in the first exodus of a handful
of people out of Africa, 50-70,000 years ago. It is now present
in every alternate Australian aborigine.
Our
study showed that 5-7 per cent of the Madurai samples carried
this marker which confirms the out-of-Africa, coastal migration
hypothesis. These results were published in the Proceedings of
the National Academy of Sciences (PNAS) in 2001.
A
subsequent wave of migration characterised by M89 marker
gave rise to Indian and Chinese populations. Another offshoot
settled in Central Asia, expanded and gave rise to present-day
Europeans, later migrant Indian populations and the American Indians.
Sir
Walter Bodmer a British geneticist and the last author
on the PNAS paper said in an interview: "We are all
descended from Africa." This put a full stop to the multiple
origin theory. The DNA of Man does not lie. One is sure of the
results which can be verified anywhere, anytime.
How
did the documentary on the genetic odyssey come about?
Spencer
Wells, the principal author, was invited to make a documentary
of these remarkable findings. The 'Journey of Man' shot
in various locations in a year's time was a monumental
story. When it aired on television in 2003, it created ripples
among scientists and commoners alike.
The
Madurai episode was the key. Following this success, Dr. Wells
convinced the National Geographic that further research with public
participation was necessary. In 2005, the Genographic Project
was launched.
Do
various populations contribute genetic samples for this research?
Ten
different laboratories around the world will collect 10,000 DNA
samples each, creating a virtual museum of human history in the
process! Apart from this, 216,000 people have purchased the cheek-swab
kit from National Geographic worldwide, learnt their migratory
pathways, and celebrated their 'heritage.'
In
India, we select distinct populations, known to anthropologists,
based on socio-cultural characteristics, language families, domicile
and isolation how far they are segregated from others in
terms of marriage etc. (The initial Madurai study involved Kallars,
Saurashtrians and Yadhavas.)
Briefly
explain the science behind the project.
In
the 3-billion-base-pair-long human DNA sequence, simple mutations
(called SNPs or VNTRs) are possible during replication.
Nucleotides
are accidentally replaced once in a while mostly copying
errors and these 'mistakes' are inherited from that generation
onwards.
These
variants can serve as genetic markers to trace migration or ancestry.
Why
is the Y chromosome, present only in men, chosen to study markers?
A
segment of the Y chromosome (NRY) does not recombine, and the
mutations, which accumulate over time, are passed on without 'shuffling'
from father to son. Hence these markers, inherited through male
lineages, are used to follow migratory splits of Man over time.
Does
the DNA of women carry the migration tale as well?
Both
males and females inherit mitochondrial DNA (mtDNA) from their
mothers. As the mitochondria of sperms does not enter the egg
during fertilization, studying mtDNA helps trace the mother's
route of migration.
What
is the larger significance of this research effort?
The
awareness 'Mankind is the same' is valuable for any nation to
live in peace and harmony.
Migratory
pathways, as determined by DNA, also correlate to the cultural
evolution of a society.
DNA
studies on fossils, complemented by archaeological excavations
could answer intriguing questions such as: Who were the Harappans?
Did the Dravidian and Indo-European languages originate in India
or arrive here?
The
broad outline of the genetic epic is clear finer details
will now emerge.
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