(CN) — The transatlantic slave trade officially ending in the 19th century, but the effects of that brutal system continue to reverberate in the genes of enslaved people’s ancestors, according to a new study.
Pairing genetic data with historical records, researchers at 23andMe can now paint a clearer picture of African ancestry in the New World, detailing the origins of enslaved Africans and the methods used to exploit them after they survived the grueling Middle Passage.
“One of the disturbing truths this research revealed was how the mistreatment of people with African ancestry shaped the current genetic landscape of African ancestry in the Americas,” stated Steven Micheletti, first author of “Genetic Consequences of the Transatlantic Slave Trade in the Americas” published Thursday in the American Journal of Human Genetics.
Researchers discovered that most Americans of African descent have roots in Angola and Democratic Republic of the Congo. This matches the historical record found in the shipping logs and other documents from the 36,000 slaver voyages that began in 1492 and continued until the early 19th century.
But a closer look at the genetic data from more than 50,000 participants on both sides of the Atlantic revealed the scope and variation of the slave trade between the Americas.
“By examining the Intra-American Slave Trade database, we concluded that much of the inferred Nigerian ancestry in the United States derives from transport of slaves within the Americas, primarily from the Caribbean,” noted senior author Joanna Mountain in a statement accompanying the study.
Other groups among the 12.5 million men, women and children forcefully deported from Africa had different results. For example, Senegambians commonly cultivated rice in their homeland, making them more likely to be sent to rice plantations in the U.S.
“These plantations were often rampant with malaria and had high mortality rates, which may have led to the reduced genetic representation of Senegambia in African Americans today,” Micheletti said in the statement.
Researchers at 23andMe also found evidence of under-documented practices, including illegal slave trading, forced segregation and the rape of enslaved African women by their owners.
“Many slave-owners in the United States promoted enslaved people having children with one another for the purpose of maintaining a workforce, and even after slavery, they tended to segregate people of African descent,” Micheletti said.
In contrast, parts of Latin America supported racial whitening, or “dilution,” after slavery was abolished, a practice that involved “women marrying lighter-skinned men with the intention of producing lighter-skinned children.”
“In the early 1900s, sources state that the Brazilian government implemented immigration laws seeking to bring more Europeans into the country, presumably to have children with darker-skinned females and reduce African ancestry,” according to the study.
Known as branqueamento, this practice is one reason researchers believe that the proportion of people with greater than 5% African ancestry is significantly lower in Latin America than in the U.S.
“Dilution” also partially explains why African women contributed substantially more to the gene pool than African men, as much as 15 to 1.
“The female bias is particularly shocking given that the majority of enslaved individuals were male,” Mountain noted.
This trend was found in North America as well, consistent with countless reports of rape and other forms of sexual exploitation of African women. In some areas, enslaved women were incentivized to reproduce with the promise of freedom following the birth of many children.
The researchers hope that the study helps those of African descent understand how the experiences of their ancestors continue to shape their communities.
“This paper conveys how the racist and dehumanizing acts endemic to the slave trade led to different patterns of African ancestry across the Americas that we can see in the DNA of people living today,” Micheletti noted.