For years, it was believed that people migrated to South America from Asia across the Bering Strait via North America and then south in a single wave, but that view has been increasingly challenged, with evidence humans arrived in America 10,000 years earlier than thought.
Now, two new studies of the distinct shapes of ancient skulls found in Brazil and Mexico suggest that the first settlers in South America arrived from multiple places in multiple waves, but not all of them mixed when they got there.
In the first study, an international team of researchers used 3D-imaging techniques to examine ancient skulls found in Lagoa Santa, the “cradle of Brazilian paleontology” in eastern Brazil. Previous research dated the skulls to between 7,000 and 10,000 years old, around the time scientists believe humans first entered South America.
Their study, published in Science Advances, discovered that the distinct shapes of these skulls didn’t match the shape of modern indigenous South Americans. They suggest that this is evidence that Brazil was populated by settlers from multiple migration events during the late Pleistocene and early Holocene, instead of the single-wave theory, as well as the possibility that it was populated from other places, such as Australia.
The second study, which shares researchers with the first and is published in the American Journal of Physical Anthropology, looked at 500 to 800-year-old skulls from the late Holocene in Mexico, which pre-date European arrival. The skulls were from three distinct regions – Sonora, Tlanepantl, and Michoacán – and threw up some unexpected results as well.
The skulls from Sonora and Tlanepantl were similar in their morphology, but the skulls from Michoacán were different. According to the researchers, this kind of variation is usually seen in populations that have been separated by thousands of years, not ones that are from roughly the same time period and geographically only 300 kilometers (185 miles) apart, which Michoacán and Tlanepantl are.
This suggests that the Michoacán population came from elsewhere to the other two, and didn’t mix on arrival, for reasons unknown. The researchers speculate that geographical features of the land at the time were not to blame as it was not considered difficult to traverse, but cultural and language barriers might have played a role.
According to Mark Hubbe of Ohio State University, who worked on both studies, it appears the populations were so reluctant to interbreed with other nearby populations for so long that these genetic differences as demonstrated by the distinct skull shape could still be seen clearly in people as little as 500 years ago.
“For whatever reason, these differences have been maintained for thousands of years,” Hubbe told New Scientist.
Both studies’ evidence of distinct differences between skull shapes of ancient settlers and indigenous modern peoples add credence to the mounting evidence that Paleoamericans – the earliest South Americans – arrived in multiple waves from multiple destinations.
“The differences between the Paleoamericans and today’s South Americans are so large that they cannot simply have appeared in 10,000 years,” Hubbe said.