In the new study, Dr. Micheletti’s team compared this genetic database to a historical one, Slave Voyages, which contains an enormous amount of information on slavery, such as ports of embarkation and disembarkation, and the number of men, women and enslaved 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, such as Angola and the Democratic Republic of the Congo. The team worked with academics connected to West African institutions to find those data.
The size of the project’s dataset is “extraordinary,” said David Reich, a Harvard professor of genetics 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 how people relate to one another” that scholars like him couldn’t ask, he said. At best, academic projects can study hundreds or a few thousand people, and generally those data do not include the genealogical information provided by 23andMe research participants.
The findings show a remarkable alignment with the historical record. Historians have estimated, for example, that 5.7 million people were transferred 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 of African descent in the Americas.
Historians have also noted that people who were brought to Latin America from Africa landed from West Central Africa, but many were originally taken from other regions such as Senegambia and the Bay of Benin. And new genetic evidence supports this, showing that the descendants of enslaved people in Latin America generally have genetic connections to 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 in Africa. Their descendants today show a genetic connection to people in six regions of Africa, the study found.
