Historical events were preserved in the human genome

An interactive map of the world's genetic history reveals the genetic effects of historical events such as the expansion of the Mongol Empire, trade along the Silk Road and the conquest of America by the Spanish and the slaves from Africa who came with them

When people from different groups have children together, the offspring's DNA becomes a mixture of DNA from each of the groups involved. Bits of this DNA pass through the generations carrying the information with them all the way to the present day.

Researchers from the Max Planck Institute for Evolutionary Anthropology in Leipzig, Germany, the University of Oxford and University College London have created a map detailing the genetic history of 95 different populations around the world over four thousand years.

The interactive world map is available online and details the histories of gene mixing between each of the 95 ecologies throughout Europe, Africa, Asia and South America. The map also shows genetic effects of historical events including European colonization, the Mongol Empire, the Arab slave trade, and European trade along the Silk Road that caused them to mix with the Chinese population.

The study published this week in the journal Science is the first to simultaneously identify the timing and characteristics of genetic mixing between populations. To this end, the researchers developed statistical methods to analyze the DNA of 1,490 people from 95 populations around the world. "DNA has the power to tell stories to reveal details about humanity's past," says Simon Myers of Oxford University's Department of Statistics and the Wellcome Foundation's Center for Human Genetics, a research partner.

"Because our approach relied solely on genetic data, it provides independent data from other sources. Many of our genetic observations are consistent with historical events and we also see evidence of undocumented genetic admixtures. For example, the DNA of the TU tribe in modern China indicates that in 1200 AD, Europeans similar to today's Greeks intermingled with the local population, who maintained the Chinese appearance. Most probably the origin of the European genetic load in China is from traders who traveled along the nearby Silk Road."

The powerful technique, known as Globetrotter, provides insight into past events such as the genetic heritage of the Mongol Empire. Historical evidence shows that the Hazaras of Pakistan are in part descendants of Mongol warriors and that research has found clear evidence that Mongol DNA infiltrated the population during the Mongol Empire. Six other populations, including those from western Turkey, showed similar evidence of admixture with Mongols at about the same time.

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"The thing that amazes me the most is just how well our technique works," said Gareth Hallenthal of the Institute of Genetics at UCL, the lead researcher. "Although individual mutations can only carry weak signals indicating where the person came from, adding the information from all over the genome allows us to reconstruct the mixing events. Sometimes people from neighboring areas can carry genetic mixtures from other sources to the patient. For example, we identified separate events that occurred several times among other Hazara groups within Pakistan, who carried genes from sub-Saharan Africa, possibly related to the Arab slave trade, as well as admixture with another population from East Asia and another with ancient Europeans. Almost all populations showed evidence of admixture events, which indicates that these were very common in history and usually involved populations that migrated over large areas.

The team used data from all 1,490 people with the goal of identifying common DNA 'blocks' for individuals from different populations. Populations that share more relatives than common will share more clusters and each such individual cluster can provide evidence as to the family relationship along the chromosomes.

"Each population shares a certain genetic 'template'" says Daniel Palush from the Max Planck Institute for Evolutionary Anthropology in Leipzig, who is also a partner in the research. "If we want to color the genes of the modern Mayans, for example, we will get a mixed pattern of colors representing the DNA of descendants of Spaniards, West Africans and Native Americans. The admixture dates to around 1670, and is consistent with historical accounts describing Spaniards and West Africans invading the Americas around the same time. Although we cannot take DNA samples from the previously intermingled populations, we can identify most of the DNA from the original groups when they are in the mixed pattern of the present-day groups."

In addition to the new insights about historical events, the new research may have implications for studying the effect of DNA on health and disease in different populations.

For the announcement on the Max Planck Institute website