By studying the genome of contemporary French people, researchers have succeeded in tracing the history of the settlement of France up to the great epidemics of the Middle Ages and the agricultural revolution of the 18th-19th centuries.
Researchers have been able to trace the settlement of France by analyzing the DNA of thousands of French people.
This article is from Sciences et Avenir magazine n°879 dated May 2020 "Special coronavirus".
We are history books. We carry traces of the past within us, buried in our DNA, and researchers have the key to deciphering this hidden information. Thus, by studying the genome of 2,184 French people from two independent studies, scientists from Inserm and CNRS have managed the feat of traveling in time to follow the population of France, to witness the epidemics that have decimated and even… fly over the rivers and mountains which have proven to be decisive frontiers for the populations.
"This is the first time that a genomic study of this magnitude has been done in France, reveals Christian Dina, specialist in genetic epidemiology at the Institut du Thorax in Nantes and one of the main authors of the study published in January 2020 in the journal European Journal of Human Genetics. I hope that this type of research can facilitate the dialogue between geneticists and historians, because genetics can provide solid information that contributes to a better understanding of the past." A dialogue that is not always easy, as explained by anthropologist Denis Pierron, who took part in a similar study in Madagascar:"The French remain very uncomfortable with the study of differences of genetic origin, unlike the Anglo-Saxons." This work, however, confirms hypotheses, while providing new data that will allow us to know more in depth the history of the country.
Rivers and reliefs are geographical barriers
First lesson of the study:genomic data confirm the existence of three waves of settlement over the millennia, as prehistorians had already established. But the researchers were also able to determine its origin by comparing the genetic information found in the contemporary sample with that found in various archaeological sites on the continent. "We have been able to establish that an initial population of Mesolithic hunter-gatherers, which had spread about 10,000 years ago throughout the region that today corresponds to France, was partially replaced by two other populations. One is from Anatolia [in present-day Turkey] during the Neolithic, about 8,000 years ago; the other, from the plains of northern Eurasia during the Bronze Age, nearly 4,000 years ago. Archaeogeneticists are currently working to date these different waves of settlement more precisely" , explains Christian Dina.
This article is from Sciences et Avenir magazine n°879 dated May 2020 "Special coronavirus".
We are history books. We carry traces of the past within us, buried in our DNA, and researchers have the key to deciphering this hidden information. Thus, by studying the genome of 2,184 French people from two independent studies, scientists from Inserm and CNRS have managed the feat of traveling in time to follow the population of France, to witness the epidemics that have decimated and even… fly over the rivers and mountains which have proven to be decisive frontiers for the populations.
"This is the first time that a genomic study of this magnitude has been done in France, reveals Christian Dina, specialist in genetic epidemiology at the Institut du Thorax in Nantes and one of the main authors of the study published in January 2020 in the journal European Journal of Human Genetics. I hope that this type of research can facilitate the dialogue between geneticists and historians, because genetics can provide solid information that contributes to a better understanding of the past." A dialogue that is not always easy, as explained by anthropologist Denis Pierron, who took part in a similar study in Madagascar:"The French remain very uncomfortable with the study of differences of genetic origin, unlike the Anglo-Saxons." This work, however, confirms hypotheses, while providing new data that will allow us to know more in depth the history of the country.
Rivers and reliefs are geographical barriers
First lesson of the study:genomic data confirm the existence of three waves of settlement over the millennia, as prehistorians had already established. But the researchers were also able to determine its origin by comparing the genetic information found in the contemporary sample with that found in various archaeological sites on the continent. "We have been able to establish that an initial population of Mesolithic hunter-gatherers, which had spread about 10,000 years ago throughout the region that today corresponds to France, was partially replaced by two other populations. One is from Anatolia [in present-day Turkey] during the Neolithic, about 8,000 years ago; the other, from the plains of northern Eurasia during the Bronze Age, nearly 4,000 years ago. Archaeogeneticists are currently working to date these different waves of settlement more precisely" , explains Christian Dina. The researchers have shown that the DNA from these three populations is indeed present in people living today in all regions of France, but in different proportions. This confirms their point of entry into the country and their progress in the territory that today constitutes France. The results thus show that farmers from Anatolia would have arrived from the south-east - due to the greater proportion of traces of their genome in this area - while the Eurasian wave would have arrived from the north, made up of nomadic herders. from the steppes north of the Black Sea. "The genetic structure of the French population was initially shaped by these migratory events, to be further refined by interbreeding and geographical barriers" , summarizes the researcher.
If the researchers were able to establish that the current population is very homogeneous, they have indeed highlighted the main cause of the few differences they were able to identify:geography. In addition to the distances which slow down interbreeding, it is above all the rivers and the reliefs which have acted as real borders. "The Loire thus seems to be the most important barrier, separating the north and the south of the country over a thousand kilometres, explains Christian Dina. It has long been a very powerful river, difficult to cross. Its valley was regularly flooded, increasing the size of this barrier by miles of mud and swamp, making the area even more difficult to cross." According to the study, the other major obstacle to gene flow has been the Garonne, a river of more than 600 kilometers with also a very high flow and few bridges or fords to cross from Aquitaine to rest of France.
Researchers are also interested in the evolution of the size of the French population over the last two millennia. Their analysis shows continuous population growth, abruptly interrupted by a period of shrinkage that began around the 14 e century to last for about 400 years. "This seems to correspond to the numerous episodes of plague that hit Europe from that time on, with - on average - one event every seven years" , explains Patrice Bourdelais, demographer and historian specializing in the study of epidemics at the School of Advanced Studies in Social Sciences (Ehess), in Paris. During this period, historians estimate that the French population fell by around 40%, which would correspond to the disappearance of 7 million inhabitants out of a total of 18 million. However, there is one point where the genetic data does not agree with the historical records. According to the results of the study, this demographic contraction is especially visible in the genome of the inhabitants of the northern part of France, which surprises Patrice Bourdelais:“Du 14 e at 16 th century, it was mainly in the south of France that the epidemics raged. There was only one major episode in the North, after this period, between 1666 and 1670:the plague was then contained north of Paris thanks to a military cordon established over more than 200 kilometers, creating a border interior which ran from Beauvais to Reims. " Has genomics brought to light a still unknown aspect of the story? It is still early to know, additional research is needed to verify these initial results.
The 3 great waves of settlement:Mesolithic, Neolithic, Bronze Age
The genomic study of France shows that its current population is very homogeneous, but with some differences, in particular on the proportion of genetic origins between the hunter-gatherers of the Mesolithic period, the farmers of the Neolithic period coming from Anatolia from the south-east. and nomadic Bronze Age pastoralists, coming from Eurasia via northeastern France. The DNA from these three populations is indeed present in contemporary people from all regions of France, but in different proportions. These genetic differences are mainly due to the two main geographical barriers in France, the Loire and the Garonne.
How is the size of ancient populations calculated?
The genomes used for the study on the origin of the French belong to the cohorts of two major health studies in France, named Su.vi.max and Three-City study. Each individual has 23 pairs of chromosomes which are mosaics made of pieces of DNA inherited from their parents, themselves having inherited them from their parents and so on. It is by studying the quantity and frequency of these different pieces in this sample of the current population, as well as their size, that the researchers managed to calculate the number of people who lived at a given time in France. In this study, they followed this transmission over 150 generations, for about 4500 years. To go back even further in the past, researchers no longer compare chromosomal pieces, but genetic mutations shared by several individuals.