All this suggests that, about 14,000 years ago, the southern lineage of early American Indians spread through the continent with blinding speed. To picture their movements, don’t think of a slowly growing tree, incrementally sending out new branches and twigs. Instead, imagine a starburst, with many rays zooming out simultaneously and rapidly.
In a matter of centuries, these people had gone down both sides of the Rockies, across the Great Basin, and into Mexico’s highlands. Within a couple more millennia, they had zipped down the Andes, through the Amazon, and as far south as the continent allowed. “Once they were south of the ice, they found a territory that was open, vast, and full of resources,” says Moreno-Mayar, who is based at the University of Copenhagen. “They were adept hunter-gatherers, so they expanded very quickly.”
This pattern confirms the suspicions of archaeologists, whose finds had long suggested that humans suddenly appeared throughout the Americas, from about 13,000 years ago onward. “You can now see that in the genetics,” Moreno-Mayar says.
Coincidentally, a second group of researchers, fronted by Cosimo Posth of the Max Planck Institute for the Science of Human History, independently found the same pattern. They studied the DNA of 49 ancient humans from Central and South America and found similar evidence for a rapid starburst expansion, and a southward migration that connects the Clovis culture of the north to early peoples in Belize, Brazil, and Chile.
These studies show that the histories of the Americas are more complicated than earlier genetic studies suggested, says Deborah Bolnick, an anthropologist from the University of Connecticut. But that’s more because those studies were overly simplistic to begin with rather than because the new results are surprising. “Many lines of evidence, including archaeological research, linguistic data, and Indigenous histories, have suggested that multiple groups of people—related, descended from shared ancestors, but still distinct—have lived, moved, and interacted in the Americas over the millennia,” she says. “Broadly, that is what these [new] studies show.”
They’re not just reinventing the wheel, though. For example, the tools of the Clovis people were so different from those found at Spirit Cave (which lies on the other side of the Rockies) that some researchers took them as evidence that the Americas were peopled by two genetically distinct founding groups. Moreno-Mayar and his colleagues have disproved that idea: They showed that the two groups were genetically similar, if culturally distinct.
Both teams also found evidence of later waves of migration that took place long after the Americas had been initially peopled—although the details differ between the two studies. Posth’s data point to a second wave of people who entered South America about 9,000 years ago, whose genes displaced those of the earlier Clovis-related people, and who had a direct connection to Indigenous groups today. By contrast, Moreno-Mayar’s data speak to a gentler process, in which relatively small groups slowly spread both north and south from Mexico from 8,000 years ago, adding their genes to the local populations without swamping them. Either way, they “challenge the idea that present-day native peoples all descend from a single, homogenous ancestral population,” says Maria Nieves-Colón, a geneticist based in Mexico’s LANGEBIO institute.