By comparing the genes of North and South Americans with African and European populations, an Oxford University study has found the genetic fingerprints of the slave trade and colonisation that shaped migrations to the Americas hundreds of years ago.
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The team, which also included researchers from UCL (University College London) and the Universita' del Sacro Cuore of Rome, analysed more than 4,000 previously collected DNA samples from 64 different populations, covering multiple locations in Europe, Africa and the Americas.
Since migration has generally flowed from Africa and Europe to the Americas over the last few hundred years, the team compared the 'donor' African and European populations with 'recipient' American populations to track where the ancestors of current-day North and South Americans came from.
While Spaniards provide the majority of European ancestry in continental American Hispanic/Latino populations, the most common European genetic source in African-Americans and Barbadians comes from Great Britain.
The Basques, a distinct ethnic group spread across current-day Spain and France, provided a small but distinct genetic contribution to current-day Continental South American populations, including the Maya in Mexico.
The Caribbean Islands of Puerto Rico and the Dominican Republic are genetically similar to each other and distinct from the other populations, probably reflecting a different migration pattern between the Caribbean and mainland America.
Compared to South Americans, people from Caribbean countries (such as the Barbados) had a larger genetic contribution from Africa.
The ancestors of current-day Yoruba people from West Africa (one of the largest African ethnic groups) provided the largest contribution of genes from Africa to all current-day American populations.
The proportion of African ancestry varied across the continent, from virtually zero (in the Maya people from Mexico) to 87% in current-day Barbados.
South Italy and Sicily also provided a significant European genetic contribution to Colombia and Puerto Rico, in line with the known history of Italian emigrants to the Americas in the late 19th and early 20th century
One of the African-American groups from the USA had French ancestry, in agreement with historical French immigration into the colonial Southern United States.
The proportion of genes from European versus African sources varied greatly from individual to individual within recipient populations.
The research team analysed DNA samples collected from people in Barbados, Columbia, the Dominican Republic, Ecuador, Mexico, Puerto Rico and African-Americans in the USA. ■