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DNA says you’re related to a Viking, a medieval German Jew or an enslaved African in the 1700s? What it means is genetic compatibility

In 2022, we reported the DNA sequences of 33 ancient people buried in a Jewish cemetery in Germany. Shortly after we made the data public, people started comparing their DNA with that of 14th century German Jews, finding many matches. These ancient people had DNA fragments shared with thousands of people who have uploaded their DNA sequences to an online database, the same way you share DNA fragments. and your relatives.

But what kind of relationship with a medieval person does a shared piece of DNA imply? 

It turns out, not much will help with your family roots research.

We are population geneticists who work with ancient DNA. We understand how exciting it can be to find a genetic link with certain people who lived many generations ago. But these DNA matches aren’t the tight ties you might think. Here is how it works.

DNA tracing of those who lived long ago

Ancient DNA is a new and rapidly growing field, awarded the Nobel Prize in 2022 to Svante Pbo for his original work.

Using samples taken from skull bones or teeth, aDNA researchers sequence the DNA of people who lived as far back as 100,000 years ago. More than 10,000 ancient DNA sequences, or genes, currently exist. These genes, from all corners of the world, have greatly changed scientists’ understanding of human origins.

A new approach to ancient DNA is the sequencing of the genes of historical people: those who lived thousands of years ago.

Examples include genes from Sweden, Norway, Denmark, Iceland, Poland, Southeast Europe, and London, Cambridge and Norwich in the UK Outside of Europe, scientists have sequenced historical genes from East Asia, Swahili coast, South Africa, Canary Islands, Lebanon. , Machu Picchu, the Caribbean and the San Francisco Bay area. The genes of enslaved Africans from Delaware, Maryland, South Carolina and St. Helena are also available.

Other historical genealogies belong to namesakes, including Ludwig van Beethoven, the family of the last Tsar of Russia, the medieval kings of Hungary, the leader of the Lakota Sioux, Sitting Bull and King Richard III of England.

a horse-drawn carriage with two figures in black in front, pulling a coffin inscribed 'Richard III, 1452-1485'
The remains of King Richard III were repatriated in 2015.
Christopher Furlong via Getty Images News

How can you compare your DNA with that of these historical people?

Several consumer-facing genetic testing companies, such as 23andMe, MyHeritage or Ancestry, make sequencing your genes easy and convenient. They compare your DNA with that of their other customers. They identify relatives who share a long, continuous stretch of identical DNA, and report these matches for you from closest to most distant.

After the first thought, 23andMe now allows customers to match their genes with historical figures. Other genetic testing companies haven’t caught up yet, but avid genealogists can do their own research. For example, the GEDmatch service allows users to upload their own DNA data, along with published DNA sequences of historical figures. Once installed, GEDmatch will identify any user with whom you share genetic information.

two lines representing chromosomes with green, yellow and red bands along their length
A comparison of the DNA chromosome sequence between a 14th century German Jew and two living people who entered their DNA into GEDmatch. Each thin horizontal bar represents one letter in the DNA sequence and is colored according to whether it matches. A shared piece of DNA appears between a living human 1 and a medieval human.
GEDMatch

So, what does a genetic comparison with a medieval person mean for your lineage?

Surprisingly, very little.

Where ancestry and genetics are different

The first thing you need to understand is how many ancestors you have in each previous generation. One generation later, he has two gods. Two generations back, that doubles to four. Now eight, and 16. In the last 30 generations, about the 12th century, you have more than a billion ancestors.

It is clear that at this time, your ancestors include many people from your population who lived at that time, excluding a small fraction who left long-term descendants. This includes, if you have European origins, notable people like Charlemagne or Edward I, but equally also people from every medieval class. Your family tree reaches each of these ancestors through many lines.

the web of red lines gets thicker and thicker towards the top of the image, the generations marked 0 to 15 go up.
The red dot at generation 0 represents a modern person in a simulated population of 100,000 people. Each red dot represents one person, and red lines connect people to their parents. Ancestors reached through multiple lines in the family tree are marked with black circles. The number of lines becomes so large that over the last 15 generations, most ancestors are reached in multiple lines.
Graham Coop

Statistical analysis reveals the following surprising fact. For any people, the number of lines that reach any medieval person is about equal between you and all the people who are part of the same people as you. In other words, everyone alive today is equally related, by lineage, to all medieval people from that community.

The next step is to understand how much DNA you inherited from your ancestors. Surprisingly, very few.

Despite your million or more medieval ancestors, you have inherited 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 picture of about 2,000 fragments, each of which goes back to a single person from the 12th century.

Who are the ancient people whose DNA you inherited? Each piece of your DNA descends from a random line up your family tree, fathers mothers fathers father etc. each generation in the past, choosing only one of the two parents. The more lines of your family that go back to a particular medieval person, the more likely you are to find DNA from that person.

family tree
For a person living today, the number of ancestors in a family doubles every generation. But each piece of DNA (colored metals) is inherited in a random, random way down the line, meaning that DNA is inherited from only a small fraction of ancestors.
Shai CarmiCC BY-ND

But remember, the number of generations that reach a medieval person is about the same for all modern people from a given society. Therefore, all people inherit DNA from any ancient person with very similar opportunities. So, sharing genes with a certain medieval person is a matter of chance, and everyone is playing the same game.

Here is an illustration. Going to the casino and rolling the roulette ball on 24 does not mean that 24 is your special number. Anyone else would have been down 24 again. Likewise, sharing a piece of DNA with anyone among millions of medieval ancestors does not imply a special relationship other than sharing a piece of DNA.

And if you don’t have a share, you’re out of luck. It doesn’t mean you don’t have a closer relationship with that ancient person than anyone else from your shared community.

On the other hand, demographics are not always well defined, but these arguments often hold for people who share a common origin.

How to interpret a historical DNA match

Consider again the German Jews of the middle ages. Some modern Ashkenazi (European) Jews will share DNA with one medieval Jew. Some will share with each other. Some will share with others. It’s a lottery game. And since most Ashkenazi Jews today are related by blood in the same way as the Germans of ancient times, seeing that a piece of DNA is shared does not mean that there is a unique blood relationship.

On the other hand, if you are willing to think about recent ancestors, DNA comparisons can be instructive. Similar mathematical models show that the number of generations that reach a certain historical person who lived about 200 or 300 years ago will vary greatly across modern people. Therefore, comparing DNA to an 18th century person means a more direct genealogical relationship, a relationship that some modern people do not have.

This trend was demonstrated in a recent study by 23andMe. By matching the genes of 18th-century enslaved Africans from Maryland to more than 9 million of their customers, 23andMe discovered more than 41,000 living relatives, including and a few more straight-laced grandchildren.

a horse-drawn carriage with two figures in black in front, pulling a coffin inscribed 'Richard III, 1452-1485'
3D models of African American slaves: one is a boy, the other is a woman in her 30s
Facial reconstruction based on the skeletons of African American slaves who worked at the Catoctin Furnace in Maryland, where scientists also sequenced ancient DNA.
Katherine Frey / The Washington Post via Getty Images

How long does DNA similarity have genealogical meaning? For example, are DNA tests 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 question, as well as to deviate from the simple one-number, freely mixed model.

In the meantime, as scientists rapidly assemble historical genetic sequences, remember the strange behavior of human generations when interpreting the DNA puzzle.

#DNA #you39re #related #Viking #medieval #German #Jew #enslaved #African #1700s #means #genetic #compatibilityEurope’s upcoming Mars rover now has a detailed map to help search for ancient life on the Red Planet (video)

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