The signposts that point back to our origins
Saturday 31 December 2011
To illustrate the story of human migration, The Independent commissioned the Genographic Project to decipher the DNA signposts hidden in the genomes of six prominent people of varying genetic backgrounds.
In this public part of project, the Genographic scientists analyse two kinds of DNA, both of which are unusual in that they do not take part in the normal "shuffling", known as genetic recombination, that goes on during sexual reproduction.
Both women and men, for instance, have DNA within their mitochondria, the tiny power houses within the cells, that are inherited only from their mothers and is not mixed with other DNA. Men have DNA on their Y-chromosomes which is not shuffled with the rest of their DNA.
Because mitochondrial DNA is not swapped around with any of the DNA found within the cell's nucleus, it retains a good historical record of mutations that have occurred in a person's ancestral maternal line. These mutations can be traced back eventually to a common female ancestor of all maternal lines, known as "Mitochondrial Eve", who lived about 150,000 years ago.
Similarly in men, the Y-chromosome does not recombine with any other chromosome, and so it too stores a good record of historical mutations that have occurred in that particular man's ancestral paternal line. The common male ancestor of all non-African men alive today is believed to have lived about 79,000 years ago and is known as "Eurasian Adam".
Sir Paul Nurse, the president of the Royal Society and a geneticist himself, chose to analyse his Y-chromosome, partly because he never knew his father, although, as he points out, this type of DNA analysis would not shed much light on his more recent ancestors. Sir Paul belongs to the typical genetic pattern, known as "haplogroup R1b, M343". Some 70 to 80 per cent of men in southern England, and up to 90 per cent in Ireland, share his haplogroup.
Bonnie Greer, the American-British playwright, belongs to the L3 haplogroup, typically found among sub-Saharan Africans today. Ms Greer has the most ancient genetic lineage in our sample and L3 seems to represent the springboard for all non-African lineages. "L3 is a really interesting lineage," said Spencer Wells, director of the Genographic Project. "It probably originated in East Africa between 80,000 and 100,000 years ago. It is the ancestor of all of the non-African genetic lineages."
Shazia Mirza, the British-Asian comedian, belongs to the M-haplogroup, one of the first groups to emerge from the African "L3" haplogroup. The M haplogroup originated in people who migrated across Arabia into the Indian subcontinent and down through Indonesia and into Australia. Dr Wells said: "M haplogroup is incredibly diverse. In fact there is more diversity in M in most of the rest of the groups put together. Everyone in south Asia is probably going to fall into M."
Ching-He Huang, the Taiwanese-born chef, belongs to the B haplogroup one of the most widely distributed genetic groups. It is found through East Asia and China, and is common among the native populations of North and South America, indicating the close genetic relatedness of native Americans with Far East Asians. Evgeny Lebedev, the Russian-born chairman of Independent Print, which publishes The Independent, and Lionel Shriver, the American author, have genotypes typically found in western Europe, after a migratory route that took their maternal ancestors through the Middle East and central Asia.
Ms Shriver's "V" haplogroup and Mr Lebedev's "H" haplogroup are survivors of the great genetic bottleneck that squeezed the European population during the last ice age. "As the ice sheets moved further south, people were forced down to southern Europe," Dr Wells added. "People took refuge in the Iberia peninsula and southern France, eventually repopulating western Europe at the end of the last ice age."
As intriguing as these findings are, this kind of genetic analysis is only a small snapshot of a tiny fraction of the human genome.
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