When a child is born, its DNA is a mixture of its parents. Those parents continue to have their DNA passed down in the generations that follow, although less and less is passed down each time. Scientists can used this pattern to figure out how two distantly related people might be related, and, interestingly, to figure out details about ancient human history, such as the occurrence of slave trades, conquests of empires, and mass migrations of people. This is exactly what was explored in a paper that came out last week in the journal Science.
By using a complex, statistical method (which the group calls “Globetrotter”) to look at the genetics of 1490 people from 95 “human groups” around the world, the researchers were able to identify over 100 human events that took place during the last 4000 years. This involved gaining details about events we already knew about, as well as learning about potential events we have no clear records of. For example, researchers could tell that modern Maya people (Native Americans living in Central American and southern Mexico) have ancestry that became mixed with Europeans (likely Spanish), West Africans (specifically the Yoruba people), and Native Americans around 1670 C.E., or about 9 generations ago. This matches speculated historic events as well as a previous, more limited genetic study.
Even older human historic events can be detected using this method, and researchers could also tell if the genetic mixing likely only happened once, or multiple times, and if it was one-way or multi-way. This directionality allows for a fairly accurate tracking of migrations. For example, the expansion of the Mongol empire (initiated by Genghis Khan) in the 1200s C.E. and early 1300s C.E. could be detected in populations of people now living in Afghanistan, other parts of Central Asia, Eastern Asia, and as far west as Turkey (the relevant genetics decreased with the westward direction, becoming a low of 8% in modern-day Turkish populations). Other ancient events were also apparent, including the Arab slave trade (where sub-Saharan Africans were taken as slaves from 890 to 1754 C.E.), complex migrations through Eastern Europe during the first millennium C.E, and migrations in Central Asia (likely between 990 and 210 B.C.E.) that indicate genetic mixing with Western Eurasians, though the precise origins could not be identified. This last event took place during the reign of Alexander the Great (356 to 323 B.C.E.), and while this predates written records, local tradition does in fact hold that the people are descendents of his army.
Unsurprisingly, the researchers found that genetic mixing has been much more common in recent times compared to ancient ones, and the more recent mixing is over larger distances.
By improving tools to allow us to better understand our history, this also gives us a better understanding of the present. For example, we can better see how a genetic disease spreads through a population, and thus be more knowledgeable about checking for, and treating, such a condition.
For further reading:
- Garrett Hellenthal et al.’s article “A Genetic Atlas of Human Admixture History“
- ScienceDaily’s article “Mixed genes: Interactive world map of human genetic history reveals likely genetic impacts of historical events”