An international team led by Harvard Medical School’s David Reich analyzed the genomes of 263 individuals in the largest study of ancient human DNA in the Americas to date. The genetics trace two major migratory waves in the Caribbean by two distinct groups, thousands of years apart, revealing an archipelago settled by highly mobile people, with distant relatives often living on different islands.
Reich’s lab also developed a new genetic technique for estimating past population size, showing the number of people living in the Caribbean when Europeans arrived was far smaller than previously thought – likely in the tens of thousands, rather than the million or more reported by Columbus and his successors.
Highlighting the region’s interconnectivity, a study of male X chromosomes uncovered 19 pairs of “genetic cousins” living on different islands – people who share the same amount of DNA as biological cousins but may be separated by generations.
Uncovering such a high proportion of genetic cousins in a sample of fewer than 100 men is another indicator that the region’s total population size was small, said Reich, professor of genetics in the Blavatnik Institute at HMS and professor of human evolutionary biology at Harvard.
“When you sample two modern individuals, you don’t often find that they’re close relatives,” he said. “Here, we’re finding relatives all over the place.”