The genes of 50,000 slave descendants reveal the effects of the global slave trade generations later, according to a study published Thursday in the American Journal of Human Genetics. The researchers analyzed data provided by thousands of 23andMe clients who agreed to share their genetic information to better understand the impact of forced migration on the genealogy of enslaved African descendants in the Americas.
They found that enslaved people who were brought from an African region to a particular region of the Americas generally ended up sharing a genetic connection to that African region generations later, said Steven Micheletti, a 23andMe population geneticist and the study’s first author.
But, in some cases, the results did not align with historical records. For example, while African Americans, based on migration documents, should show genetic roots closely linked to present-day Angola and the Democratic Republic of the Congo, many show genetic links closer to Nigeria.
The high percentages of Nigerian descent in African Americans in the US may be related to the number of slaves that were transferred from the British Caribbean to the United States. This was supported by historians who cited a “database on the intra-American slave trade, which made it clear that slaves had been brought from the Caribbean to the United States,” said Joanna Mountain, research director at 23andMe. “When you look back at the pattern of slaves brought to the Caribbean, especially the British Caribbean, you see that it was often from Nigeria.”
Dr. Bernard Powers, historian and director of the Center for the Study of Slavery in Charleston, part of the College of Charleston in South Carolina, suggests that the origin of slaves sent from the Caribbean to the United States may be difficult to trace . But he said the genetic mismatch may be the result of migrations of people from what is now southeastern Nigeria to parts of Angola and Congo that were later captured and shipped to the United States.
There could have been “internal developments within the African continent, which shaped the export” of slaves, Powers said. “Each of these regions has its own political and economic as well as climatic history, and variations could contribute to the export of people on the coast.”
Powers and the researchers agree that once slaves from Angola and the Democratic Republic of the Congo arrived in the United States, they suffered high mortality rates in rice plantations where malaria and horrible working conditions were common. “Rice was really the most labor-intensive crop produced in colonial America, for sure,” Powers said. “It would have been the continent’s approach to sugar cultivation in the Caribbean.”
Mountain suggested that high mortality rates may have contributed to reducing the genetic representation of enslaved people in Angola and the Democratic Republic of the Congo in African-Americans.
Despite the differences in slavery practice between countries and colonies across the Americas, the researchers also found a general sexual bias that appeared on all continents.
“Sexual prejudice is basically the ratio of African women who are reproducing to African men,” said Micheletti. “African women reproduced much more than African men. That is indicative of rape and exploitation that has been documented in newspapers and other historical literature. “
Researchers acknowledge that their data lacks representation of global populations due to 23andMe’s mostly customer base in the US However, they say looking at genetics through the lens of historical data could uncover new truths about ancestry.
“We don’t want these historical details to be swept under the rug,” said Micheletti. “We really want them to be discussed today, and adding genetic confirmation to those details could be a powerful tool.”
