Analysis of the genome of individuals buried in a collective grave in Bréviandes-les-Pointes, near the French city of Troyes, has revealed a significant story with far-reaching implications. Research published in the journal Science Advances shows that the final phase in the formation of the European genome is still present in many of today's Europeans.

The human genome encompasses the totality of genetic information carried by our DNA, reflecting the history of our ancestors. The genome of today's Europeans has been formed over more than 40,000 years, as a result of various migrations and population mixing. It consists of a complex inheritance from small groups of hunter-gatherers who inhabited Europe until the arrival, about 8,000 years ago, of populations from Anatolia and the Aegean region, descendants of those who invented agriculture and animal domestication in the Fertile Crescent. These Neolithic farmers interbred with local hunter-gatherers and significantly contributed to the genome of many of today's Europeans.

At the end of the Neolithic, between 5,000 and 4,000 years ago, nomadic populations from the Pontic steppes (north of the Black Sea, stretching from the Danube to the Urals) migrated to Europe and contributed the third major component of the genome that has persisted in Europeans through the following millennia to the present.

Although sequencing genetic information is a routine process today, this method is challenging for the genomes of people from the past. Only more or less fragmented skeletons remain of them, and some parts of these skeletons may contain preserved traces of DNA, but it is fragmented and scarce, posing a methodological challenge for analysis.

Our team at the Jacques Monod Institute took on this challenge and optimized methods to obtain reliable results. This allowed us to analyze ancient genomes using the most advanced bioinformatics and statistical methods.

Testimony of population mixing
Our analysis of the genomes of seven individuals from the grave in Bréviandes, combined with bone morphology analyses conducted by anthropologists from Inrap, showed that the grave contained:

- A woman over 60 years old
- Her son, an adult man aged about 20-39 years
- Her grandson, aged about 4-8 years
- The grandson's mother, aged 20-39 years
- A younger woman aged 20-39 years
- The newborn of the younger woman
- A child aged between 6-10 years

The last three individuals were not related to the others in the grave, and the last child was not related to anyone else. The fathers of the adult man, the newborn, and the lone child were not present. Therefore, it can be assumed that this is not the grave of one biological family. On the other hand, all the women carried a hereditary component characteristic of populations of southern France and southwestern Europe, and this shared origin outside the grave area could explain why they were buried together with their children.

Additionally, the genome of the adult man was divided between the French Neolithic roots of his mother and the genome of nomadic steppes north of the Black Sea from his father. These nomads migrated to central Europe about 5,000 years ago and interbred with local Neolithic populations before continuing their migration east, north, and northwest of Europe. In the genomes of seven individuals buried in the grave, we can almost "in real-time" observe the introduction of the genome of steppe nomads into the area of the Neolithic population.

This exceptional situation, previously undescribed, allowed us to reconstruct part of the genome of the adult man inherited from his father, who was not present in the grave and therefore could not be directly analyzed. The genomic signature of this absent father places his origin in northwestern Europe. We previously obtained a similar result for another man of steppe origin, who was buried in the Aisne Valley at the same time. These two men could therefore belong to the same population.

Since the genomic signature of the adult man's mother is associated with the Neolithic populations of southern France, the grave in Bréviandes testifies to the encounter in the area of the future city of Paris, during the late Neolithic, between people migrating from north to south and vice versa.

Two main phases of mixing
Expanding the analysis to already published ancient genomes from other European regions allowed us to model these migrations of steppe populations. The results suggest that there were two main phases of mixing during the 3rd millennium BC. The first phase of mixing occurred between steppe nomads and Neolithic farmers who created characteristic globular-shaped pottery with two to four handles. It is assumed that this happened in eastern and central Europe about 4,900 years ago.

Their mixed descendants developed a new archaeological culture, known as the "corded ware culture," named after clay vases decorated with cord impressions before firing. This culture combined elements of the globular amphora and steppe cultures, including burying the dead in individual graves. The practice of making corded ware then spread east and north of Europe with people from the mixed Neolithic-steppe population. During their migrations from east to west of Europe, they mostly interbred with each other rather than with native farming populations.

The second phase of mixing with native populations is assumed to have occurred 300 to 400 years later in western Europe, about 4,550 years ago. In both cases, mixing most often occurred between migrating men and local women. The beginning of this second phase we managed to identify in the grave in Bréviandes-les-Pointes.

Thanks to the analysis in the same study of the burial of an adult man in Saint-Martin-la-Garenne (east of Paris), we were also able to show that the mixing that occurred played a key role in transforming the European genome.

The man was buried according to burial rituals characteristic of the Bell Beaker culture (BBC), with characteristic bell-shaped vases found in numerous graves. This culture developed in western Europe (between the southwest and northwest) before spreading throughout Europe and North Africa. He was buried with a BBC type of slate, an addition for archers, identifying him as a person of high social status. He was of steppe origin, and from his genome, we could conclude that his mother carried even more steppe origin than he did. This indicates that these populations organized marriage networks with groups from other regions whose members had more steppe origin. At the end of the Bell Beaker period, around 2000 BC, most of the men analyzed carried the Y chromosome of steppe peoples, which is still the majority among French men today.

The genome of all today's Europeans who have lived in Europe for generations, along with the Neolithic part, also contains a part of this steppe origin. This presence is more pronounced in northern Europe than in southern Europe.

In conclusion, the two most intense phases of genetic mixing between migrating steppe populations and indigenous populations are associated with the creation of new cultures, corded ware and Bell Beaker culture. The latter was the first true pan-European culture. These encounters and mixings led to the formation of a genome characteristic of many of today's Europeans.

Original:
Eva-Marija Geigl
Research Director CNRS, co-responsible for the Epigenome and Paleogenome team at the Jacques Monod Institute, Université Paris Cité
Oğuzhan Parasayan
Postdoctoral researcher, Pasteur Institute
Thierry Grange
Research Director CNRS, co-responsible for research team, Jacques Monod Institute, Université Paris Cité