Analysis of the remains of 49 people has revealed that there were at least three major immigration waves from North to South America, instead of just one, as scientists previously believed.

Researchers to date only knew of the first migrants, who arrived in South America at least 11,000 years ago. But DNA analysis published in Cell on November 8 suggests that a second group of settlers replaced the first about 9,000 years ago. And a third group arrived in South America around 4,800 years after that.

An international team of geneticists, including those from the Harvard Medical School in the US and the Max Planck Institute for the Science of Human History in Germany, analyzed the genomes of the skeletal remains of 49 people found in Belize, Brazil, the Central Andes (which includes parts of Ecuador, Bolivia, and Peru), and the Southern Cone of South America (which includes Argentina, Chile, Uruguay, and parts of Brazil). Of those 49, 41 were more than 1,000 years old.

Not only did this work reveal the three distinct flows of genes to South America, researchers also found that, around 9,000 years ago, the genes from the first wave of migrants almost totally disappeared. This suggests that the second wave of migrants replaced the first, though it’s not clear how this happened.

A separate study of 15 different human genomes found in the Americas, ranging from modern-day Alaska to Patagonia (six of which were older than 10,000 years) published on the same day in Science, shows the movement of populations across the continent. The research also showed that some of the remains found in Brazil had an indigenous Australasian genetic biomarker. The scientists hypothesize that the genetic connection between ancient Australasians and ancient Brazilians is due to migrants traveling by land. But, as there are no genetic traces of this journey from any skeletal remains in between the two continents, it’s still a mystery.

That said, one thing is clear: these ancient people were moving fast. “People were spreading like a fire across the landscape and very quickly adapted to the different environments they were encountering,” Eske Willerslev, geneticist at the Natural History Museum of Denmark in Copenhagen and co-author of the Science study told Science News.

The two papers are some of the first to show the intricate variation of movement among the populations that made up the first migrants to South America. “I think this series of papers will be remembered as the first glimpse of the real complexity of these multiple peopling events,” Ben Potter, an archaeologist at the University of Alaska-Fairbanks who was not involved in the study told Nature. “It’s awesome.”