The world's most exhaustive map has been made detailing genetic histories of 95 different populations across the world revealing genetic impact of European colonialism, Arab slave trade, Genghis Khan's empire and European traders near the Silk Road mixing with people in China.
The map produced by researchers from Oxford University and UCL details the histories of genetic mixing between each of the 95 populations across Europe, Africa, Asia and South America spanning the last four millennia.
Scientists have been saying that Khan and his armies had a genetic impact across Asia but previous analyses were based on more limited genetic data.
Over 10 years ago, comparisons of Y chromosome lineages across Europe and Asia showed that a large number of Asian men shared a common Y chromosome. The breadth of the distribution of this haplogroup, and the extrapolation that roughly 0.5% of the world's population carried the same Y chromosome together with age estimates led to the idea that Khan himself might have left a lasting genetic impact across Asia.
More recently a study using genome-wide data with different methods and genetic markers but on a similar (but smaller) set of populations found evidence of admixture in the Uighurs dating to the time of Genghis Khan.
"As well as the Uighurs, we found evidence of this Mongolian expansion in a further six populations. These populations approximately span the maximum spread of the Mongol empire. Taken together we believe that there is now strong evidence that this event had a major impact on many Eurasian populations," scientists said.
The study identified dates and genetic mixing between populations. To do this the researchers developed sophisticated statistical methods to analyse the DNA of 1490 individuals in 95 populations around the world.
"DNA really has the power to tell stories and uncover details of humanity's past," said Simon Myers of Oxford University.
"Because our approach uses only genetic data many of our observations match historical events and we also see evidence of previously unrecorded genetic mixing. For example, the DNA of the Tu people in modern China suggests that in around 1200 CE, Europeans similar to modern Greeks mixed with an otherwise Chinese-like population. Plausibly the source of this European-like DNA might be merchants travelling the nearby Silk Road," he said.
The technique christened Globetrotter provides insights into past events such as the genetic legacy of the Mongol Empire. Historical records suggest that the Hazara people of Pakistan are partially descended from Mongols and this study found clear evidence of Mongol DNA entering the population during the period of the Mongol Empire. Six other populations from as far west as Turkey showed similar evidence of genetic mixing with Mongols around the same time.
Garrett Hellenthal of the UCL Genetics Institute said, "Although individual mutations carry only weak signals about where a person is from by adding information across the whole genome we can reconstruct these mixing events. For example we identify distinct events happening at different times among groups sampled within Pakistan with some inheriting DNA from sub-Saharan Africa perhaps related to the Arab Slave Trade, others from East Asia and yet another from ancient Europe. Nearly all our populations show mixing events so they are very common throughout recent history and often involve people migrating over large distances".
According to the map, the group with the longest time since admixture of different DNAs is detected are the Kalash from Pakistan with an ancient inferred event prior to 206 BCE involving mixing between a more European and West Asian group and a more Central/South Asian group.