A 4,500-year-old tomb reveals the secrets of the last phase of the formation of the "European genome"

Analysis of the genomes of individuals buried in a 4,500-year-old common tomb at Bréviandes-les-Pointes near the French city of Troyes has yielded new and surprising information: The final stage of European genome formation between migrants from the steppes and the natives is still present in many modern Europeans.

The human genome is a collection of genetic information that partly reflects the history of our ancestors. The genome of modern Europeans has been shaped over more than 40 000 years by various migrations and mixing of populations. It carries the genetic information of small populations of European hunters and gatherers who began to interbreed with farmers from Anatolia and the Aegean region about eight thousand years ago. At the end of the Neolithic, between 5 000 and 4 000 years ago, nomadic populations migrated from the Pontic steppes to Europe, contributing the third major component of the genome that has persisted in Europeans to the present day.

Although sequencing genetic information is routine today, the process is much more complicated in archaeology. Few skeletons have survived that may carry traces of DNA, but it is very fragmented and "sparse". The team at the Institut Jacques Monod has therefore optimised the DNA analysis using the latest bioinformatic and statistical methods to obtain the most accurate results.

The analysis of seven individuals from the Bréviandes tomb, combined with research on bone morphology, showed that the tomb contained the remains of a woman aged 60, her son aged around 20-39, and her grandson aged 4-8. Furthermore, the tomb contained the mother of a grandson aged 20-39 years, a young woman aged 20-39 years, her newborn child, and finally a child aged 6-10 years.

The last three were not related to the others and the last child was not related to anyone in the tomb. All the female skeletons bore a hereditary component characteristic of the populations of southern France and southwestern Europe. The adult male's genome carried information from his French Neolithic mother and his father's genome from nomadic steppe peoples north of the Black Sea. These nomads migrated into central Europe about 5,000 years ago and interbred with local Neolithic populations before continuing eastward into north and northwest Europe.

Within these seven individuals in the tomb, we observe an almost "real-time" introduction of the steppe nomad genome into the Neolithic population. The genome of the (tomb-absent) father of the adult male places his origins in northwestern Europe. Since his mother belonged to the Neolithic populations of southern France, the Bréviandes tomb bears witness to the encounter of individuals migrating from north to south and back during the last Neolithic period.

Extending the analysis to already published genomes from other European regions has made it possible to model the migrations of steppe peoples. The results suggest that two major waves of interbreeding occurred during the 3rd millennium BC. The first wave took place between steppe nomads and Neolithic farmers of the spherical amphora culture in eastern and central Europe around 4,900 years ago. Their descendants created a new archaeological culture known as the 'corded pottery culture'.

The new culture combined elements of both previous cultures, including the burial of the dead in individual graves. The practice of making cord pottery subsequently spread from Europe to the east and north, along with individuals of mixed Neolithic steppe populations. During migrations from east to west Europe, they were more likely to reproduce among themselves than with settled farming populations.

A second wave of interbreeding with the original populations occurred 300 to 400 years later in western Europe around 4 550 years ago. In both cases, the most common interbreeding was between migrants and indigenous women. The beginning of this second wave can be observed in the Bréviandes-les-Pointes tomb. The analysis of the burial of an adult male in Saint-Martin-la-Garenne has also shown that this mode of interbreeding played a major role in the transformation of the European genome.

The man was buried together with a slate wrist guard for archers, indicating the high status of the owner. He was laid to rest according to the rites typical of the bell jar culture, with characteristic pottery discovered in numerous other graves. This culture originated in Western Europe, after which it spread throughout Europe and North Africa.

His genome showed that his mother had even more steppe ancestry than he did. At the end of the Bell Jar culture period around 2000 BC, most of the men analysed had the Y chromosome of steppe peoples, which is still the majority among French men today. The genome of all contemporary Europeans living here for many generations contains, in addition to the Neolithic, a part of steppe origin, which is particularly pronounced in northern Europe.

The study's findings show that the two most intense phases of genetic interbreeding among migrants from the steppes with the indigenous populations are each associated with the emergence of a new culture - with corded pottery and spherical amphorae. The former was a truly pan-European culture. These encounters and interbreeding led to the creation of a genome that is characteristic of many Europeans today.

Roman Nemec

Sources: phys.org, pnas.org, science.orgLink to study: https://www.science.org/doi/10.1126/sciadv.adl2468

Mass burial at Bréviandes les Pointes

A mass burial at Bréviandes les Pointes

a) Map showing the geographical location of the samples b) Estimated age of death and uniparental information haplogroup c) Relationships between individuals d) Pedigree charts with gene component of steppe and Neolithic ancestry.jpg