With two vast continents before them, occupying the Caribbean was not the top priority of the first people to reach the Americas. Once those islands became too inviting, new evidence shows, settlement came in a series of waves from different directions, with genetic evidence that populations remained largely isolated from those nearby for thousands of years.
Until recently, attempts to make sense of Caribbean settlements relied on archeological information such as changing tools and artistic styles. Advances in genetics have allowed a seven-nation collaboration to draw a more detailed picture using the genomes of 93 people living on the islands between 3,200 and 400 years ago.
The warm, wet climate of the region degrades DNA quickly, and scientists have struggled to obtain more than small sequences of genomes from the island's skeletons. Using a method known as hybridization capture, the team were able to match variations at many different places in the genome. Combined with more easily obtained mitochondrial DNA, this provides considerable information about the ancestry of the bones from which the fragments come.
The Caribbean was initially populated around 8,000 years ago. The team reports in Science that the first arrivals probably came from the west, followed by a second wave from the same direction. A third wave came from South America 2,800 years ago. The new inhabitants did not cut lose their continental connection after arriving, however.
"Big bodies of water are traditionally considered barriers for humans and ancient fisher hunter gatherer communities are usually not perceived as great seafarers,” said first author Kathrin Nägele, a PhD student at the Max Plank Institute for the Science of Human History, in a statement. “Our results continue to challenge that view, as they suggest there was repeated interaction between the islands and the mainland,”
When Europeans colonized the Caribbean, a combination of introduced diseases and deliberate slaughter wiped out most of the previous inhabitants. There is no evidence of anything similar when new populations arrived from either American continent. On the other hand, the authors found little sign of the intermingling that might be expected.
"Although the different groups were present in the Caribbean at the same time, we found surprisingly little evidence of admixture between them," said the Institute's Dr Cosimo Posth.
Only one individual, a Puerto Rican living around 1,000 years ago, was found to have ancestry from both lines. Indeed, the third wave may have only reached Cuba shortly before the Spanish, despite having populated islands to the east more than 2,000 years earlier.
The third, South American, wave was already known to archaeologists, having brought pottery and other new technologies to the islands. However, the fact there were two previous migrations from Meso-America, rather than one, was previously not recognized. The authors think one of these is related to a dispersal occurring within North America around the same time.