What the DNA of Native Americans reveals

For decades, textbooks have told a relatively simple story about the original human settlement of the Americas. According to this narrative, a group of humans from Asia crossed the Bering region thousands of years ago and, over time, gradually expanded throughout the continent, from north to south. Now, however, one of the most ambitious genomic studies conducted on the descendants of Native Americans suggests that this story is much richer and more complex than previously thought.The research, led by Tábita Hünemeier, a population genetics specialist at Pompeu Fabra University, which involved more than two dozen researchers from around the world, has analyzed complete genomes of indigenous populations from various Latin American countries. According to their publication in the journal Nature, they have discovered more than a million new genetic variants that were absent in large international databases. The result is not only an advance in understanding human history, but also highlights the extent to which a significant part of global human genetic diversity had been practically absent from biomedical research.

When we hear about the human genome, it's easy to imagine that science already has an almost complete catalog of the genetic variability of our species. But the reality is more complicated. For many years, most genomic studies have focused on populations of European origin. This has led to many other populations being underrepresented in the databases used to research diseases, develop treatments, or reconstruct human evolutionary history.

The descendants of the first American nations constitute one of the most evident examples of this lack. Despite representing one of the great branches of human diversity, they continued to be one of the least studied groups from a genomic point of view. To correct this situation, Hünemeier and his collaborators sequenced 128 complete genomes from 45 indigenous populations distributed across eight Latin American countries: Mexico, Colombia, Brazil, Peru, Bolivia, Paraguay, Ecuador, and Argentina. These groups represent 28 different linguistic families, an extraordinary cultural diversity that until now had almost no equivalent in genetic studies.

The surprise came when they compared these sequences with large international databases. They identified more than 1.4 million genetic variants that had not been previously described. In other words, millions of small differences in human DNA had gone unnoticed simply because the populations that carried them had never been studied. This does not imply that they have extraordinary characteristics. It shows that scientific knowledge about human genetic diversity is still incomplete. As if an archaeologist were trying to reconstruct a Roman mosaic by observing only pieces of a single color.Clues about the settlement of America

The study also offers new insights into how the American continent was populated. Genetic data indicate that its history is not linear. Evidence compatible with multiple human dispersals towards South America has been identified, followed by processes of regional differentiation and also long periods of population continuity. This concept is particularly interesting because it suggests that many American communities have maintained remarkable genetic continuity for thousands of years.This does not mean that there were no population movements or cultural exchanges, but rather that historical reality was much more diverse and less simplistic than some traditional models indicate. One of the most intriguing aspects is the confirmation of a genetic signal that had already sparked debate in previous research. Some indigenous American populations share certain genetic variants with current groups from Australasia, a region that includes Australia, Papua New Guinea, and various Pacific islands.

It does not necessarily mean that there were direct voyages between Polynesia and America or vice versa thousands of years ago, even though explorers like Thor Heyerdahl demonstrated that they were possible using only traditional vessels. Heyerdahl embarked on a traditionally made raft and sailed with five other companions from Peru to the atoll of Rairoa in Polynesia. What this study suggests is that the ancestral populations that gave rise to the first American settlers could have been much more diverse than previously thought, or that very ancient episodes of genetic mixing occurred that we do not yet fully understand.Beyond the fascination that human history arouses, this work has very practical implications. Modern genomic medicine increasingly relies on large databases to identify risk factors, diagnose diseases, and develop personalized treatments. When certain populations are absent from these databases, their members may be partially excluded from the benefits of biomedical research. This is why the authors insist that expanding genetic representation is not just a scientific issue, but also one of equity. Better understanding human diversity allows for the construction of more precise and inclusive medicine.