Ancient Human Skulls Crack Open an Epic Migration Story

Ancient human skulls from Brazil are telling a new story about the epic migrations of early people, whose lives might have been spent on the move.

Cutting-edge 3D renderings show that early South Americans shared a recent common ancestor with modern Asians, showing just how far nomadic communities moved from place to place.

A study detailing the findings was published Wednesday in the journal Science Advances.

The research also sheds light on the modern-day Brazil’s earliest settlement patterns and the genetic ancestry of modern Native Americans. The findings also support a theory that multiple — up to four — migrations into the Americas happened, instead of a single wave of people coming through.

How South America Was Populated

We know that South America was the last continent to be populated by modern humans, but how it was populated remains a divisive subject.

The group of researchers analyzing cranial data from Paleoamericans in Brazil’s Lagoa Santa region examined diversity among skull samples they say can be explained by multiple migrations (as opposed to just local diversification). The samples show that the last common ancestor is shared by contemporary northeast Asian populations.

“I knew that suggestions about multiple migrations had been made based on the unusual shape of the Paleoamerican skulls, and the wide variation seen in South America — but I approached the project with an open mind,” first author Noreen von Cramon-Taubadel tells Inverse.

“I think one of the biggest impacts of this research on the issue of human diasporas moving forward, is the method we have developed can be applied in any context where we have human fossils and want to test what the most likely ancestry of that fossil is, in the context of global human diversity,” she explains.

Von Cramon-Taubadel and her co-authors began the project in 2013. Their 3D skull-shape representations focused on three distinct cranial regions:

• The vault

• The face

• The basicranium

It was by analyzing those areas that they discovered the Paleoamerican’s last common ancestor was not, as might be expected, within the Americas.

Existing research has suggested a genetic link between Australasians and some Amazonian populations, and this shared Asian ancestor supports the idea that not all the region’s inhabitants arrived at the same time, but the majority of the genetic information we currently have supports a single-wave theory. New data like this suggests that there’s too much variation between early Paleoamericans and modern Native Americans to be explained by just one migration.

“So we tested this idea by using a new model-testing approach that takes skull variation from the whole world into consideration,” writes von Cramon-Taubadel. “Our results suggest that people entered South America several times in prehistory, which shows how complicated migration history within the Americas actually is.”

Anthropologists have been using these kinds of 3D morphometric techniques for decades, but von Cramon-Taubadel explains that the specific method she uses, geometric morphometrics, has really taken off only in the last 15 or 20 years, as the technology becomes more compact and affordable. She collects her data using a hand-held 3D digitizer, which in the last few years have been increasingly replaced by 3D structured light and laser scanners.

Von Cramon-Taubadel and her colleagues can’t say yet how far apart the migration waves might have been, or about how long it took for the morphology to diversify — at least not yet. The next step is to apply the same 3D imaging methodology to fossil data and, hopefully, contextualize those fossils in the bigger picture of modern human diversity.

Abstract

The nature and timing of the peopling of the Americas is a subject of intense debate. In particular, it is unclear whether high levels of between-group craniometric diversity in South America result from multiple migrations or from local diversification processes. Previous attempts to explain this diversity have largely focused on testing alternative dispersal or gene flow models, reaching conflicting or inconclusive results. Here, a novel analytical framework is applied to three-dimensional geometric morphometric data to partition the effects of population divergence from geographically mediated gene flow to understand the ancestry of the early South Americans in the context of global human history. The results show that Paleoamericans share a last common ancestor with contemporary Native American groups outside, rather than inside, the Americas. Therefore, and in accordance with some recent genomic studies, craniometric data suggest that the New World was populated by multiple waves of dispersion from northeast Asia throughout the late Pleistocene and early Holocene.