In 2022, we reported the DNA sequences of 33 medieval people buried in a Jewish cemetery in Germany. Not long after we did the publicly available datapeople began comparing their own DNA with that of 14th-century German Jews, finding many “matches.” These medieval individuals had fragments of DNA shared with thousands of people who uploaded their DNA sequences to an online database, much like you share fragments of DNA with your relatives.
But what kind of relationship with a medieval person does a shared DNA fragment imply?
It turns out that there is not much that helps in researching family roots.
We are population geneticists who work with ancient DNA. We understand how exciting it can be to find a genetic link to specific people who lived many generations ago. But these DNA matches aren’t the close ties you might think. See how it works.
Sequencing DNA from those who lived a long time ago
Ancient DNA is a new and rapidly growing field with a Nobel Prize awarded in 2022 to Svante Pääbo for his fundamental work.
Using samples taken from skull bones or teeth, DNA researchers can sequence DNA of people who lived 100,000 years ago. More than 10,000 ancient DNA sequences, or genomes, are currently available. These genomes, which come from all corners of the world, have dramatically revolutionized scientists’ understanding of human origins.
A new trend in ancient DNA is the sequencing of the genomes of “historical” individuals: those who lived during the last millennium.
Examples include genomes of Sweden, Norway, Denmark, Iceland, Poland, Southeast EuropeIt is London, Cambridge It is norwich in the United Kingdom Outside Europe, scientists have sequenced historical genomes of East AsiaO Swahili coast, South AfricaO Canary Islands, Lebanon, Machu PicchuO Caribbean and the San Francisco Bay Area. Genomes from enslaved Africans Delaware, Maryland, South Carolina It is Saint Helen are also available.
Some historical genomes belong to named individuals, including Ludwig van Beethoventhe family of last Russian tsar, medieval Hungarian Royal membersthe Lakota Sioux leader Sitting Bull It is King Richard III from England.
How could you compare your own DNA to that of these historical people?
Several direct-to-consumer genetic testing companies, such as 23andMe, MyHeritage, or Ancestry, make reading your own genomic sequence simple and affordable. They compare your DNA with that of other customers. They identify relatives they share with you long, continuous stretches of identical DNA and report these matches to you – from the closest to the farthest.
After initial deliberation23andMe now allows customers compare your genomes to historical people. Other genetic testing companies don’t yet do this, but passionate genealogists can take matters into their own hands. For example, the service GEDmatch allows users to upload their own DNA data along with published DNA sequences of any historical person. Once uploaded, GEDmatch will identify any user with whom you share genetic material.
So what does a genetic match with a medieval person mean for your genealogy?
Surprisingly, very little.
Where genealogy and genetics diverge
The first thing to understand is how many ancestors you had in each past generation. A generation ago, you have two ancestors. Two generations ago, that doubles to four. Then, eight and 16. 30 generations ago, around the 12th century, we already had more than a billion ancestors.
Clearly, at this point, your ancestors include most of the people in your population who lived at that time, excluding a small fraction who left no long-term descendants. This includes, if of European origins, notable people such as Charlemagne or Edward I, but equally also people from all medieval social classes. Your family tree reaches each of these ancestors through numerous lines.
Mathematical research demonstrates the following surprising fact. In any population, the number of lines in your family tree that reach back to any specific medieval person is approximately the same between you and everyone else who belongs to the same population as you. In other words, all people alive today are equally related, genealogically, to all medieval people in that population.
The next step is to understand how many ancestors you actually inherit your DNA from. Surprisingly, again, very few.
Despite your millions or more medieval ancestors, you inherit DNA from only a small fraction of them. So, sorry, you probably didn’t inherit any DNA from Charlemagne or Edward I. For example, you only have about 2,000 genetic ancestors from the 12th century. In other words, your DNA sequence is a mosaic of approximately 2,000 “fragments,” each dating back to a single person from the 12th century.
Who are the medieval people whose DNA you inherited? Each fragment of your DNA descends from a random line in your family tree – your mother’s father, your mother’s father, and so on – in each generation in the past, randomly selecting one of the two parents. The more lines in your family tree go back to a particular medieval person, the more likely you are to inherit that person’s DNA.
But remember, the number of family lines that reach a medieval person is approximately the same for all current individuals in a given population. Therefore, all individuals inherit the DNA of any medieval person with very similar probabilities. So sharing genetic material with a given medieval person is just a matter of luck, and everyone is playing the same game.
Here’s an analogy. Going to a casino and rolling a roulette ball for 24 doesn’t mean that 24 is your special number. Anyone else could have gotten 24 as well. Likewise, sharing a fragment of DNA with any of the millions of medieval genealogical ancestors does not signify any special relationship – beyond sharing a fragment of DNA.
And if you don’t have a shared thread, you’re just out of luck. This does not mean that you are any less genealogically related to that medieval person than anyone else in your population who has a common thread.
As a side note, a “population” is not always well definedbut these arguments are generally valid for people with similar backgrounds.
How to interpret a historical DNA match
Let us consider medieval German Jews again. Some present-day Ashkenazi (European) Jews will share DNA with a particular medieval Jew. Some will share with others. Some will not share with anyone. It’s a lottery draw. And given that most Ashkenazi Jews today are genealogically related in a very similar way to medieval German Jews, seeing that the shared DNA fragment does not imply any unique genealogical relationship.
On the other hand, if you’re willing to consider more recent ancestors, DNA matches can be informative. The same mathematical models show that the number of family lines that reach a given historical person who lived about 200 or 300 years ago will be very different among people today. Therefore, a DNA match with an 18th century person implies a more specific genealogical relationship, which most other modern-day individuals do not have.
This pattern was demonstrated in a recent study by 23andMe. By comparing the genomes of enslaved 18th-century Africans from Maryland with more than 9 million of its customers, 23andMe discovered more than 41,000 living relatives, including some almost direct descendants.
How long does a DNA match still have genealogical significance? For example, are DNA matches informative in the period between the late Middle Ages and the 17th century? We don `t know yet. Future research will be needed to clarify this issue, as well as deviations from the simple model of a single, freely mixed population.
However, as scientists rapidly accumulate more and more historical genome sequences, keep in mind the peculiar behavior of human genealogies when interpreting a DNA match.
This article was republished from The conversation, an independent, nonprofit news organization that brings you trusted facts and analysis to help you understand our complex world. It was written by: Shai Carmi, Hebrew University of Jerusalem It is Harald Ringbauer, Max Planck Institute for Evolutionary Anthropology
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Shai Carmi is a paid consultant and holds stock options on MyHeritage.
Harald Ringbauer does not work for, consult with, own shares in or receive funding from any company or organization that would benefit from this article, and has disclosed no relevant affiliations beyond his academic appointment.
