Scientists have mapped the effects of war, colonization, trade, migration and slavery on the genetic mixing of humans over the bulk of recorded history and created an online interactive atlas of humanity's genetic history.
In a paper published Thursday in the journal Science, researchers detailed the genetic mixing between 95 populations across Europe, Africa, Asia and South America during 100 historical events over the last 4,000 years.
The events covered in the interactive atlas include the expansion of the Mongol empire by Genghis Khan, the Arab slave trade, the so-called Bantu expansion into Southern Africa, and European colonialism.
When people from different groups interbreed, their offspring's DNA becomes a mixture of both admixing groups. Scientists say pieces of this DNA are passed down to following generations, although the size of the segments become smaller and smaller.
By studying the size of the DNA segments in present-day humans, researchers can infer how long ago it was that the admixture occurred.
"Each population has a particular genetic 'palette.'" said study co-author Daniel Falush, an evolutionary geneticist at the Max Planck Institute for Evolutionary Anthropology in Leipzig, Germany.
"Though we can't directly sample DNA from the groups that mixed in the past, we can capture much of the DNA of these original groups as persisting, within a mixed palette of modern-day groups," he said in a prepared statement.
To accomplish this, researchers used a sophisticated statistical method called "Globetrotter" to analyze genome data from 1,490 individuals.
While genetic signals obtained from a single individual might be relatively weak, they strengthen as scientists look at a larger group. As a result, researchers found that their genetic data matched historical events and periods.
One such example involved the legacy of the Mongol empire, researchers said. Traces of Mongol DNA in the Hazara people of Pakistan support historical accounts that the Hazara descended from Mongol warriors.
In populations surrounding the Arabian Sea, researchers detected mixing with sub-Saharan Africans between AD 890 and 1754. That period seemed to coincide with Arab expansion and slave trade, the authors said.
In other cases, the researchers found mixing that escaped the notice of historians.
"The DNA of the Tu people in modern China suggests that in around [AD] 1200, Europeans similar to modern Greeks mixed with an otherwise Chinese-like population," said co-author Simon Myers, a bioinformatics and statistics expert at Oxford University.
"Plausibly, the source of this European-like DNA might be merchants traveling the nearby Silk Road," he said.
Of the 95 populations studied, 80 showed evidence of admixture, while nine groups could not be characterized by the statistical method, researchers said.