DNA tests reveal genetic impact of African slave trade

The Black Lives Matter movement has highlighted the damaging legacy of colonialism and slavery on people of African heritage around the world. Now, a major DNA study has shed new light on the fate of more than 12 million Africans who were traded as slaves to the Americas between the 16th and 19th centuries.

More than 50,000 people of African ancestry on both sides of the Atlantic took part in the DNA study, which was able to identify details of the ‘genetic impact’ the slave trade has had on today’s populations. The findings were published in the American Journal of Human Genetics.

Steven Micheletti, a population geneticist at 23andMe, told AFP news agency that the aim of the study was to compare the genetic results with the manifests of slave ships. It is believed that more than 12.5 million Africans were traded between 1515 and the mid-19th Century. Of these, around 2 million of the enslaved men, women and children died en route to the Americas.

While much of their findings agreed with historical documentation about where people were taken from in Africa and where they were enslaved in the Americas, “in some cases, we see that they disagree, quite strikingly”, said Mr Micheletti.

Roots of African slaves pinpointed

The study found, in line with the major slave route, that most Americans of African descent have roots in territories now located in Angola and the Democratic Republic of Congo. What was surprising was the over-representation of Nigerian ancestry in the USA and Latin America when compared with the recorded number of enslaved people from that region.

Researchers believe this can be explained by the intercolonial slave trade that occurred primarily between 1619 and 1807. It is thought that enslaved Nigerians were transported from the British Caribbean to other areas to maintain the slave economy as transatlantic slave-trading was increasingly prohibited.

Likewise, the DNA researchers were surprised to find an under-representation from Senegal and The Gambia, which was one of the first regions from where slaves were deported. This could be accounted for because of their high mortality: many were sent to work in rice plantations where malaria and other dangerous conditions were rampant. In addition, in later years larger numbers of children were sent, many of whom did not survive the crossing.

In another grim discovery, the DNA study found that the treatment of enslaved women across the Americas had had an impact on the modern gene pool. A strong bias towards African female contributions in the gene pool (even though the majority of slaves were male) could be attributed to the rape of enslaved African women by slave owners and other sexual exploitation.

In Latin America, up to 17 African women for every African man contributed to the gene pool. Researchers put this down in part to a policy of ‘branqueamento’, racial whitening, which actively encouraged the immigration of European men “with the intention to dilute African ancestry through reproduction”.

Although the bias in British colonised America was just two African women to one African man, it was no less exploitative.

The study also highlighted the practice of coercing enslaved people to have children near the abolition of the transatlantic trade as a means of maintaining an enslaved workforce. In the USA, women were often promised freedom in return for reproducing.

This DNA investigation of the transatlantic slave trade establishes genetic links between individuals in the Americas and populations across Atlantic Africa to better understand their African roots. It could be the first of many DNA investigations as pressure increases to learn more about this dark episode of history.

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