Some 300 years ago, three African slaves died on the Caribbean island of Saint Martin, with no record of who they were or where exactly they came from. After centuries enduring harsh Caribbean weather conditions, the chances of ever identifying them were slim. Now, researchers from Stanford have used a novel technique to identify the slaves’ origins – they extracted DNA from their tooth roots.
“We have long sought to use DNA to understand who they were, where they came from, and who, today, shares DNA with those people taken aboard the ships. This project has taught us that we cannot only get ancient DNA from tropical samples, but that we can reliably identify their ancestry. This is incredibly exciting to us and opens the door to reclaiming history that is of such importance,” said Carlos Bustamante, PhD, professor of genetics at Stanford.
The new technique is something called whole-genome capture, which allowed researchers to isolate DNA in specimens that are typically unusable. Even in the case of the tooth roots – typically better insulated from contamination than other parts of the body – the scientists were only able to recover short, fragmented sequences of DNA.
Whole-genome capture works by exposing the DNA sample to a genome-wide panel of human-specific RNA molecules to which the degraded DNA in the sample can bind (not unlike using a magnet to concentrate iron in iron-rich dirt). They then used something called principal component analysis, which compared the slaves’ DNA sequences with a reference panel of 11 West African populations.
“We were able to determine that, despite the fact that the three individuals were found at the same site, and may even have arrived on the same ship, they had genetic affinities to different populations within Africa,” said Stanford postdoctoral scholar Maria Avila-Arcos, PhD.. “They may have spoken different languages, making communication difficult. This makes us reflect on two things: the dynamics of the trans-Atlantic slave trade within Africa, and how this dramatic, ethnic mingling may have influenced communities and identities in the Americas.”
As for the enslaved men? They found that one likely belonged to a Bantu-speaking group in northern Cameroon, while the other two were genetically similar to non-Bantu-speaking groups, probably in present-day Nigeria or Ghana.
The technique may not be enough to tell us exactly who these men were, but at least we now know where they came from.