Skull Analysis Concludes the Americas Were Settled by More than One Wave of Migrants
Has there ever been a more exciting adventure than when humans spread out across the globe with their primitive tools and not so much as a hand-drawn map? A new study of cranial shapes of prehistoric people shows it’s possible there were several migrations of Asians and possibly Australian or Polynesian people who undertook this great trek into the Americas thousands of years ago.
The researchers’ paper says prehistoric human skull morphology of earlier South Americans more closely resembles Polynesian or Australasian peoples. They write that the cranial shapes can fill in gaps that scientists may never be able to close with studies of genes and DNA.
There is a contentious debate between anthropologists and Native Americans about whether there was one migration into the Americas via the Bering Strait land bridge between Alaska and northeastern Russia many thousands of years ago. That land bridge has been under water for millennia. Some researchers say the people of one big mass migration were the ancestors of all natives of the Americas.
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Many natives deny this theory and say the people came to what they call Turtle Island from many places. This new research supports their viewpoint.
The map shows the location of contemporary population and the Paleoamerican sample from Lago Santa in Brazil. ( Noreen von Cramon-Taubadel, Andre Strauss and Mark Hubbe )
This latest research was conducted by anthropologists Noreen von Cramon-Taubadel, André Strauss and Mark Hubbe and published by Science Advances journal. Their position is that people came to South America from more than one place and/or from several migrations through Beringia.
The team employed geometric morphometric imaging processes to create three-dimensional images of some skulls from the Lagoa Santa region in Brazil. Those skulls have been estimated to date to around 7,000 to 10,000 years ago—around the time of the arrival of people in South America.
An ancient skeleton discovered in the region of Lagoa Santa in Brazil. ( Lago Santo Museum of Archaeology )
The great differences in skull shape from modern, native South Americans indicate one of two possibilities, the authors write. The first is that the skull shapes varied so greatly as a result of genetic drift or natural selection acting in small isolated populations. As they write :
“The other main hypothesis proposed is that the observed cranial diversity is the result of multiple waves of dispersion into the Americas from northeast Asia over the course of several thousand years, with each wave of migrants introducing new sources of biological diversity. This argument is largely based on the empirical observation that the average cranial shape of the earliest South Americans bears stronger affinities with Australasian and Polynesian populations than it does with East Asian or later Native American groups.”
The authors point out that South America was the last continent populated by humans, but the cranial differentiation of these people is unusually high relative to the people of other continents.
The researchers wrote in their report that the nature and timing of the colonization of the Americas is subject of a long-running debate.
“It is now clear that people entered the Americas from northeast Asia via Beringia by at least 15,000 years ago, and dispersal into South America proceeded quickly, most likely following a coastal Pacific route,” they wrote. “A genetic distinction between western and eastern South American populations has been noted, particularly with respect to a signal of Australomelanesian ancestry in eastern (Amazonian) populations. This is consistent with our cranial findings, which suggest a layered population history for South America, with at least two major sources of biological variation from Asia.”
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The earliest migrants into the Americas were quite distinct from later people in their morphology. The researchers say gene flow among early migrants and later peoples may have been a factor in their assimilation around 11,000 years ago or during the Holocene.
They write that because relevant genomic data is not available for many questions about human prehistory, cranial shape data may be the best bet for drawing conclusions about the past.
A map of gene flow in and out of Beringia, according to 2007 data on human mitochondrial DNA haplogroups. Colors of the arrows correspond to approximate timing of the events and are decoded in the colored time bar. (Erika Tamm et al/ CC BY 2.5 )