How the slave trade shaped Americans’ ancestry

It's common knowledge that the ancestors of many people living in North and South America today came from Europe and Africa. But a new Oxford University study offers brand new details on exactly how the slave trade and colonization shaped this heritage.

"We found that the genetic profile of Americans is much more complex than previously thought," Oxford University professor and study author Cristian Capelli said in a press release announcing the results.

He and a team of researchers evaluated 4,000 DNA samples from 64 populations, comparing the genes of current-day North and South Americans with those of current-day Europeans, to track the origins of the Americans' ancestry. Here's what they found about what they called the "genetic fingerprints of the slave trade and colonisation":

• Members of American populations who identify as Hispanic/Latino and those who identify as African-American both have European ancestry — but it's from different sources. The most common European genetic source in Hispanic/Latino populations is Spain, while the most common European genetic source in African-American populations (as well as people from Barbados) is Great Britain.
• The largest contribution of African genes to current-day American populations is from the Yoruba people of West Africa. Study author Garrett Hellenthal, of the University College London Genetics Institute, explained, "The majority of African Americans have ancestry similar to the Yoruba people in West Africa, confirming that most African slaves came from this region. In areas of the Americas historically under Spanish rule, populations also have ancestry related to what is now Senegal and Gambia. Records show that around a third of the slaves sent to Spanish America in the 17th Century came from this region, and we can see the genetic evidence of this in modern Americans really clearly."
• One of the African-American groups studied in the United States had French ancestry, which lines up with the fact that French people immigrated to the colonial southern United States.

• The proportion of African ancestry varied wildly across North and South America. Researchers found that it's virtually zero in the Maya people of Mexico, and 87 percent in Barbados.

'We can see the huge genetic impact that the slave trade had on American populations," said Hellenthal, "and our data match historical records."

Further reading

• Here's where "white" Americans have the highest percentage of African ancestry
• Here's when you can expect racial minorities to be the majority in each state
• 11 ways race isn't real

WATCH: 'Inside the big business of searching for ancestors'

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