Unravelling mysteries of ancient human migrations

From: http://www.hindu.com/seta/2007/08/23/stories/2007082350011500.htm

Aug 23, 2007

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.