The history of African-Americans has been shaped in part by two great journeys.

The first brought hundreds of thousands of Africans to the southern United States as slaves. The second, the Great Migration, began around 1910 and sent six million African-Americans from the South to New York, Chicago and other cities across the country.

In a study published on Friday, a team of geneticists sought evidence for this history in the DNA of living African-Americans. The findings, published in PLOS Genetics, provide a map of African-American genetic diversity, shedding light on both their history and their health.

Buried in DNA, the researchers found the marks of slavery’s cruelties, including further evidence that white slave owners routinely fathered children with women held as slaves.

And there are signs of the migration that led their descendants away from such oppression: Genetically related African-Americans are distributed closely along the routes they took to leave the South, the scientists discovered.