Am I Related to a Viking? The Reliability of Genetic Ancestry Testing
Sharp drops in the costs of DNA sequencing in the last fifteen years have driven radical developments in the way we use genetics to investigate the past. But what exactly can genetic ancestry testing tell us about historic peoples and ourselves?
The Rise of DNA testing in the 21st Century
Analysis of DNA extracted from ancient human remains was something exceptional a decade ago but is now a relatively routine part of archaeology. At the same time, the rise of Direct-to-Consumer DNA testing has seen millions of us exchanging spit and money for an account of our personal genetic ancestries.
It may feel as though this new supply of ancient and modern DNA sequences should enable us to make direct biological connections to our ancestors that reveal ‘who we really are’. Indeed, early marketing by some genetic testing companies exploited this, claiming to be able to tell you whether or not you were a ‘Viking’.
However, the idea that the true essence of a person and their sense of identity should boil down to a genetic link with a poorly-defined group of people from the past is highly suspect, and represents a misunderstanding of what genetic ancestry is.
The Problem with Personal Genetic Ancestry Tests
Genetic ancestry tests don’t compare your genetic data against ancient genomes. Instead, they usually compare your data against living people whose grandparents were all born in a particular area.
This method is an attempt to capture the genetic variation of people who lived in that area in the past by gathering data from source populations who live there in the present. It’s reasonable to think that the genetics of these source populations are somewhat representative of past peoples, but this is largely an untested assumption.
This means that personal genetic ancestry tests mainly tell you how similar your genome is to that of living people with recent ancestral connections to a particular part of the world.
The way in which source populations are selected and trimmed (using a computer algorithm) means that they are a conservative estimate of past genetic diversity and are probably not entirely representative of any historical or living group of people.
How Far Back Can I Reliably Trace My Ancestry Through Genetics?
If we were to accept the assumption that these genetic ancestries are providing some signature of past peoples, how far back do they go?
Our number of genealogical ancestors increases exponentially as we go back each generation, yet the total size of the population decreases. Eventually you reach the genetic ‘isopoint’ when everyone from a particular region who produced descendants is the genealogical ancestor of everyone alive today with ancestry from that region.
For people with recent ancestry from Europe, the genetic isopoint is estimated to be the 10th Century AD. This means that if you are someone who has any recent ancestry from Europe, everyone from 10th-Century Europe who produced descendants is your genealogical ancestor.
You may be wondering, if people with recent ancestry from Europe all have exactly the same ancestors going back 1,000 years, why is their genetic ancestry not identical? That’s because we don’t inherit DNA from most of our distant genealogical ancestors. While your genome contains a vast amount of information, it’s finite and there’s only space for a limited number of genetic ancestors.
Instead, your genetic ancestry is largely representative of your recent genealogical ancestry, within the past 300 years or so. You have, of course, inherited some DNA from distant ancestors that has survived this generational whittling.
While your distant genealogical ancestors were inevitably dispersed across huge geographic regions, there is a much higher chance that you have inherited DNA from the small minority who lived in areas inhabited by your recent ancestors. Because of this, your genetic ancestry will reflect the more recent populations of these regions.
Commercial genetic tests are not without their uses, however. They are a powerful tool in genealogical research and can be used to identify distant living ancestors with whom you share tiny sections of DNA, helping to fill gaps in family trees where traditional documentary research has fallen short.
Can comparing my genetic information against ancient genomes offer a greater insight into our ancestral connections with prehistoric peoples?
No. In some ways this would be more misleading than using modern source populations. It would provide no further insight into your individual ancestral origins than when comparing your genome against modern source populations.
Any affinities you share with distant ancient individuals or populations will simply reflect the population histories of the areas where your recent ancestors lived. It might also give you a false impression of a meaningful and specific ancestral connection with ancient groups.
Moreover, studies of ancient DNA illustrate this point nicely in showing that human genetic diversity has been forged by repeated episodic mixing between genetically diverse peoples. For instance, in prehistoric Britain (including the region we now call Scotland) there were at least two major population movements from continental Europe. These migrations resulted in an almost total transformation of local genetic ancestries.
What this means is that most people who live in Scotland today are not descended from, for instance, the people who erected the Stones of Stenness or who lived at Skara Brae. This does not in any way diminish the status of these places as ‘Scottish’ heritage, but it does expose the problems of a simplistic understanding of genetic ancestry as defining your sense of heritage and belonging.
Then why are there big studies into ancient DNA?
Sophisticated analysis of genetic ancestries amongst specially selected groups of living people can give insights into the population histories of certain regions of the world, as demonstrated by the University of Edinburgh and the Royal College of Surgeons.
They examined the genomes of people born in the 1940s and 1950s, whose grandparents or even great-grandparents were all born in the same region of Scotland, to investigate past genetic variation at a very fine scale.
Lerwick, Shetland (© Duncan C via Flickr, CC-BY-NC-2.0)
When we pool together genetic ancestries from a select group of people, we can make some inferences about the history of human populations in those regions, but importantly, for the reasons above, these genetic ancestries do not give you a complete idea of the deep ancestral history of an individual.
Using ancient and modern DNA to investigate population structures and how they develop through time is useful and important for understanding present-day genetic variation and how groups of people moved and interacted in the past. Also, genetic variants associated with certain diseases can occur more commonly amongst people with particular genetic ancestries, while showing up rarely in others.
Therefore, sampling from a wide range of genetic ancestries can help us home in on genetic variants that predispose people to disease.
Is there such thing as “Scottish” DNA?
One way in which the Edinburgh study was reported was in terms of which regional group was genetically the most ‘Scottish’. It’s easy to see the appeal of this approach in making the genetic results directly relatable to the public, but there’s no such thing as ‘Scottish’ DNA. The definitions of ‘Scotland’ and ‘Scottish’ have also shifted through time, even in the recent past.
Instead, the reporting of ‘Scottish’ DNA refers to a series of genetic ancestries found amongst this select group of people who took part in the study, and who had documented ancestral connections to certain regions of Scotland going back a defined length of time.
It’s been suggested that these ancestries are somewhat similar to the genetic ancestries of people who lived in Scotland in the distant past, but this is just an assumption, especially when a study hasn’t included any ancient genomes.
The clean room in the ancient genomics laboratory at the Francis Crick Institute (Credit: Kyriaki Anastasiadou)
This kind of framing may seem like a great way to get people to read about the research, but it unwittingly promotes the harmful idea that the legitimacy of your national identity is dependent on the depth of your genetic connection to a particular place, and that there is a hierarchy of ‘Scottishness’ that can be distinguished from your DNA.
This idea stems from an overly romantic vision of DNA which casts ancient genetics as a mythical origin story of peoples rather than as one bit of evidence amongst many which contribute to our understanding of the history and heritage of a particular place.
Can genetic ancestry testing reveal a person’s ‘true‘ identity?
Human genetics and particularly ancient DNA continues to produce marvelous new information about the histories of humans all around the world, most of which would otherwise have been unknown or unknowable.
However, this genetic information does not have any exceptional intrinsic value when it comes to modern ideas about identity, heritage, nationhood and belonging, beyond what that we decide to project onto it.
Genetic ancestries are, by their nature, fluid and ever changing. They are not a stable foundation for the construction of identity in the modern world.
We had been happily creating and recreating notions of identity, belonging and heritage for millennia before we sequenced the human genome, and it would be a strange and disturbing break with the past to put genetics at the heart of these discussions now.
Ready to dig deeper? Find out more about what DNA testing can tell us about human remains from the past.
By Dr Tom Booth, a Senior Research Scientist in the ancient genomics laboratory at the Francis Crick Institute. Dr Booth is an archaeological scientist working on a Wellcome Trust-funded project which is sequencing the genomes of at least 1,000 people who lived in Britain over the last 6,000 years. The results will be used to investigate population change and natural selection in Britain over time
Further Reading
– David Reich, 2018. Who we are and how we got here: Ancient DNA and the new science of the human past. Oxford University Press.
– Adam Rutherford, 2016. A Brief History of Everyone Who Ever Lived: The Stories in Our Genes. Weidenfeld and Nicolson.
– VIKING Genes Project at The University of Edinburgh
Header Image: Shutterstock
