In the new study, Dr. Micheletti’s team compared this genetic database with a historical one, Slave Voyages, which contains an enormous amount of information about slavery, such as ports of embarkation and disembarkation, and numbers of enslaved men, women and children.
The researchers also consulted with some historians to identify gaps in their data, Dr. Mountain said. Historians told them, for example, that they needed representation from critical regions, like Angola and the Democratic Republic of Congo. The team worked with academics connected to West African institutions to find that data.
The size of the project’s dataset is “extraordinary,” said David Reich, a professor of genetics at Harvard who was not part of the project.
Because it drew participants from a direct-to-consumer database of millions of people, the study was able to “ask and answer questions about the past and about how people are related to each other” that could not be asked by academics like himself, he said. At best, academic projects are able to study hundreds or a few thousand people, and generally that data does not also include the genealogical information that the 23andMe research participants provided.
The findings show remarkable alignment with the historical record. Historians have estimated, for example, that 5.7 million people were taken from West Central Africa to the Americas. And the genetic record shows a very strong connection between people in West Central Africa and all people with African ancestry in the Americas.
Historians have also noted that the people who were taken to Latin America from Africa disembarked from West Central Africa, but many were taken originally from other regions like Senegambia and the Bight of Benin. And the new genetic evidence supports this, showing that the descendants of enslaved people in Latin America generally carry genetic connections with two or three of these regions in Africa.
Historical evidence shows that enslaved people in the United States and the British Caribbean, by contrast, were taken from a larger number of regions of Africa. Their descendants today show a genetic connection to people in six regions in Africa, the study found.