Putting together the Neolithic puzzle

Past human migrations have always been a subject of great interest because they tell us a story of where we come from, and who we are. What were the past movements that gave rise to the global human landscape that we observe today?

                               Ancient DNA charts human migration

Traditional archaeology lacks the most detailed document of the history of life on earth: DNA. And modern genetics lacks a time perspective – you are trapped in time as you can only study what you see around you.

Molecular Archaeology or Archaeogenetics, is a new field that allows you to travel back in time and directly study the DNA of humans or animals within the archaeological record.

This has now opened the possibility to directly track ancient human migrations by analysing the genetic composition of past populations.

Among the subjects that I have been recently working on are the Peopling of the Americas and the 'Neolithisation' of Europe: that is, the origin of agricultural societies. Both involve past human migrations.

The Peopling of the Americas is of particular interest because this was the last mass of land on earth to be populated by humans.

But who were these people? Where did they come from? Are all Native Americans direct descendants of one single migration wave that populated the Americas only one time? Or were there several initial migration waves originating from different places?

For example, is the difference in genetics, or in physical characteristics or even languages that we observe throughout the whole continent the result of different ancestral origins?

By using the latest molecular technologies, the field of Molecular Archaeology has been unravelling some of the stories behind the past human migrations.

Local links with the Americas

In one of our latest publications we demonstrated that all modern Native Americans are descendants of one single migration wave that took off from Siberia no earlier than 23,000 years ago, travelled throughout the Bering Strait land bridge, made a stop over in the region for about 8,000 years, and then entered into the Americas around 15,000 years ago.
 
It was only once they were inside the American continent that they separated, around 13,000 years ago, and started to form some of the populations patterns observed today.

One of the most striking findings of this study was the detection of genetic links between some modern populations of Native Americans and people related to Australo-melanesians in Southeast Asia.

New World not completely isolated from Old

This finding implies that the New World was not completely isolated from the Old World after the initial migration wave that populated the Americas.

On a related subject, through ancient DNA analysis, we can also put an end to highly debated controversies on different 'skull shapes' indicating a different ancestry or origin.

Two of the most highlighted cases are the famous Kennewick man, a Native American approximately 9,000 years old. One of the main controversies surrounding this individual was the physical characteristics of his skull, which according to some people, resembled the shape of a European skull, not a Native American.

Similarly, the Pericúes, an extinct ethnographic group from Mexico, showed particularities on their skull shapes that led some authors to suggest that these were more related to Australo-melanesians, rather than Native Americans.

With this physical evidence, came suggestions of different origins of the initial people that arrived in the Americas. Our genetic results, however, demonstrate that they are Native Americans and that their skull shapes are not related to different genetic origins. These results were published in Nature and Science this year.

Eastern migration into Europe

Regarding the origins of agriculture in Europe, there has been a long-standing debate whether the arrival of agriculture in Europe from the Near East was the result of a human migrations or a cultural exchange between incoming farmers and native hunter-gatherers.

We have learnt (from early mitochondrial DNA analyses and more recent nuclear genome analyses) that hunter-gatherers and early farmers are two distinctive genetic groups. This indicates that agricultural practices in Europe arrived with incoming farmers who replaced in most cases native hunting and gathering people.

However, this was not a complete population replacement. These two groups mixed (interbred) with some hunter-gatherers incorporated into the new farming populations.

In this new study published in PNAS this week, we explore this scenario in the furthest western frontier in Europe, the Iberian Peninsula.

We analysed the genomes of farmers who lived during the Copper Age, between 3,500-5,500 years, in Spain. The human remains were found at the Cave of El Portalón from the world famous site of Atapuerca.

Hunter-gatherers mixing it with farmers

We found that farmers in Iberia interbred with local hunter-gatherers for thousands of years, but what was more surprising was that the levels of this mixing became greater through time.

When comparing this within Spain, we found that the closest living relatives to these ancient Iberian farmers were the Basques who have long been considered as European outliers.

For example, their language is completely different from Indo-European languages, and they are genetically distinct from other Iberian populations.

It has even been suggested that they are directly descended from the Palaeolithic era 10,000 years ago. But as a result of this study we now know their closest ancestors were in the Neolithic, and therefore are not that ancient. This means that Basques must have remained relatively isolated during the last 5000 years.

Most importantly, it is only a matter of time before we have a nearly complete genetic landscape of the Neolithic in Europe, a period characterised as the basis of all modern societies  – and of the world as we know it today.

Dr Cristina Valdiosera is a Molecular Archaeologist at La Trobe University in Melbourne. She is joint lead-author of in international research team that has just published a new study on early Europe in the Proceedings of the National Academy of Sciences in the US. This article was first published in ABC Science On Line.

Caption: Dr Valdiosera working at El Portalón cave in Atapuerca, Spain.

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