Tracing Europe’s genes

The papers may be full of stories about refugees coming to Europe, fleeing war and hardship in other parts of the world, but when we look back through history, this is nothing new. A new study led by researchers at the University of Oxford shows that there's been extensive immigration into and around Europe for centuries, revealed by the mish-mash of variations in the DNA of today's Europeans, as Kat Arney hears from study lead author Cristian Capelli...

Cristian - Basically, what we do is to look for fragments of DNA that are present in human population that are shared with other populations. This sharing could possibly be the result of events of gene flow that occurred in the past.

Kat - And by gene flow, presumably, you also mean people flow.

Cristian - When people move close to each other, also a result an exchange of genes. So yes, the result of gene flow in this case, is also the result of people migrating and getting in contact, and exchanging genes, yes.

Kat - Exchanging genes sounds very romantic.

Cristian - Well, I would say that's yes.

Kat - How many people did you actually look at and what sort of level of detail were you going into to look at their DNA, to look at their genomes and see what bits have come from where?

Cristian - Well, we looked at approximately 2,000 people. A thousand of them pretty much coming from western Eurasia and a thousand coming from a side of this area.

Kat - How have you gone about analysing the DNA of these 2,000 people that you've looked at?

Cristian - Well, the classical approach is to use the samples according to the label that has been provided when the samples have been collected. For example, Italians. what we instead have done is that we used their genetic data to identify the groups that we wanted to analyse. In this way, we removed any possible subdivision that was present in the sample. So in this way, basically, we removed some level of confounding that could be present. In this way, we're able to maximise our chance to identify the signature that we were interested in.

Kat - So broadly, paint me a picture of what your results show about the different populations in this area.

Cristian - We found signatures that are related to what we already know in the history of Europe but also, evidence for episodes that are not well-recorded in the history of the region. So for example, presence of North African genes in Iberia in a period that is related to the presence of the Muslim kingdom in Spain and Portugal. At the same time, we also found contributions from Africa in Spain and in southern Italy that are at a different time and a later time. Such contribution is not present in the history books. So, we're somehow surprised but at the same time excited because we were able to identify those different events. But at the same time, we see that a lot of those events that are occurring within Europe are centred around a thousand years ago that seems to be a period in time where there was a lot of things happening in the continent as well. A lot of migration, contacts, and possible gene flow occurring and leaving those signature across the population in the area.

Kat - How well does your data tie up with information from other sources, from other genetic studies or historical studies?

Cristian - Well, as I said, there are a number of events that align very well. Others seems to be less relevant in terms of the genetic contribution. As for example, one thing that we noticed was that despite the fact that the Romans have been conquering very much Europe, North Africa, and the Middle East at a certain point in time, there's nothing like a Roman contribution, that might be an Italian contribution, scattered across Europe in a systematic way. Clearly, there is a difference between cultural and political occupation and on the other side, the demographic impact that those events might have had. So, there's no clear answer to your question in a sense that yes, we see a lot of events that align very well. But also, we found a lot of events that we don't know anything about, specifically from the history of this region of the world.

Kat - Cristian Capelli from the University of Oxford, and that study was published in the journal Current Biology.