Why Do Native Australians and the Amazons Share a Genetic Link?

September 4, 2015 | Gillian Burrell

Map displaying the proposed migration route of the most recent ancestors of the Amazons and native Australians.
Photo credit: The Science Explorer

Two independent groups of scientists have discovered a surprising genetic link between natives of the oceanic region and the Amazons but the explanation is a topic of hot debate.

Separated by approximately 19,000 km of water, Oceania and the Amazon are literally on opposite sides of the world. So when researchers at Harvard and the Natural History Museum of Denmark in Copenhagen noticed genetic similarities between natives of the two regions, they were intrigued. According to the two studies, published yesterday (July 21) in Science and Nature, we may need to rethink our understanding of how Homo sapiens migrated across the continents.

The current theory behind the settlement of the Americas suggests that, during the last glacial period, a drop in sea levels exposed terrain between Alaska and Russia. Called the Bering Land Bridge, this 1,000km wide strip of land is believed to have connected the two continents and facilitated a single wave of migration from Northern Asia to colonize the Americas. All Native Americans (except the Inuit) are thought to be descended from these "First Americans" but recent data suggests that there is more diversity among American populations than previously thought. 

At the end of the last ice age, melting glaciers caused ocean levels to rise and the Bering land bridge sank below the sea (credit: NOAA).
 Gif displaying the changing landscape at the Bering Strait over the last 21,000 years

According to the Harvard researchers the genetic data indicates two waves of migration; sometime after the First Americans arrived on the continent, a group of people called Population Y also crossed the land bridge.  By combining genetic data from members of present-day Amazonian tribes, the researchers reconstructed what they think Population Y's genes would have looked like—and they're nothing like other Native American groups. Instead the genes resemble those of Native Australians and New Guineans.

If this data is accurate, it would support the Paleoamerican Theory stating that a group of ancient humans from Asia divided into two populations just before crossing the Bering Strait. The first group split in two again, giving rise to both the Australo-Melanesians, who travelled south, and Population Y, who crossed the bridge and ended up in Brazil. At the same time or a little later, the other group (the First Americans) crossed the strait to spread across North, Central, and South America.

Unfortunately, to prove their hypothesis, the researchers need to recover DNA from an actual member of Population Y— a find that is highly unlikely. "The Amazon is quite possibly the worst place imaginable for DNA preservation, with its humid climate," explains lead author, Pontus Skoglund in an interview with Nature News. His best hope is to test previously uncovered skeletons from that time period, some of which have been described as Australian in appearance.

Contrary to Skoglund's theory, researchers in Denmark believe that the second wave of migration occurred more recently: less than 9,000 years ago. As published in Science, the authors found similarities to Australian genes in the indigenous populations of the Aleutian Islands, suggesting that a second wave of migration came through Alaska towards Brazil. The problem with this theory, however, is that it requires the Amazon ancestors to travel from Alaska to Brazil without mixing with any previously established populations.

Regardless of whose theory is correct, both papers agree on a few points: first, that no ancestral Australians ever crossed the Pacific Ocean by boat; secondly, that indigenous Americans crossed the Bering Land Bridge no more than 23,000 years ago; and lastly, that the First Americans split into a Northern and a Southern population.



Based on materials provided by the University of California – Berkeley and Harvard Medical School.


Hot Topics

Facebook comments