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Chaotic Past Gave Us Human Diversity

Posted By Prucia Buscell, Thursday, February 20, 2014

Invading armies, the slave trade, merchant travel on the Silk Road, the flight of refugees and the rise and fall of ancient empires have left indelible traces in the lives of people today. Geneticists using new statistical techniques to unravel the surprising results of the world-wide mixing of human populations over the last 4,000 years have created a human genetic atlas published in the journal Science.

Genes tell stories of humanity's past. The Kalash people of Pakistan today have bits of DNA from an ancient European population. The Kalash and several other groups in the region are the likely descendants of soldiers of Alexander the Great, who invaded India in 326 BCE. The Arab slave trade is the likely source of segments of African origin in the genomes of people who live today in the southern Mediterranean and parts of the Middle East. That trade began in the seventh century, and many slaves were absorbed into host populations. European ancestral genes were probably brought to the Tu people of central China between the eleventh and fourteenth centuries by traders traveling the Silk Road. Scientists say the rise of the Mongol Empire and the invasion of Mongol hoards conquering new territories is one of history's most wide-spread population mixing events. Alterations in the human genome have emerged through centuries of the chaotic events we call history.

A team of scientists led by Simon Myers of Oxford University, Garrett Hellenthal of University College of London, and Daniel Falush of the Max Planck Institute for Evolutionary Anthropology in Germany sampled genomes round the world and discovered they could identify 95 distinguishable populations.

While all humans have the same set of genes, a New York Times story by Nicholas Wade explains, our genomes are "studded with mutations, which are differences in the sequence of DNA units in the genome." Whole sets of mutations are passed from parent to child, so certain patterns become common in certain populations. When people from different populations marry, their children's genomes have big chunks of DNA from each parent's ancestry. The size of the chunks decreases with each successive generation, as the DNA of the parents' genome is swapped during the chemistry of reproduction. Geneticists looking at the size of the different chunks can calculate how many generations have passed since the introduction a new mutation. That allows them to identify an approximate date when the populations mixed.

The European colonization of America is recorded in the genomes of the Maya and Pima Indians, the story says, and the genomes of Cambodian populations record the invasion Tai people and the fall of the Khmer Empire in the fifteenth century. The English are known to have a rich history of ancestral invaders, but because they were genetically similar to the English, scientists have not yet been able to identify specific mixing events. While scientists who created the genetic atlas did not work with historians, they hope their discoveries will be useful in historical research and discovery. Read the Times story here. Read a Christian Science Monitor story here, an abstract of the Science story here and see an interactive map here.

A man is whole encyclopedia of facts. The creation of a thousand forests is in one acorn, and Egypt, Greece, Rome, Gaul, Britain, America, lie folded already in the first man. -Ralph Waldo Emerson

Tags:  buscell  complexity matters  culture  research 

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