Two large samples were used to analyze modern French population genetics in a recent preprint
. The core results are as follows (references omitted, style altered to reflect American style conventions in some instances, and omissions of details made as indicated, images from the paper):
Pie charts indicating the proportion of individuals from the different “départements” assigned to each cluster. Results are reported for the partition in 6 clusters obtained by running FineSTRUCTURE. Geographic coordinates of three rivers of France are drawn in black: Loire, Garonne and Adour from north to south.
important division separates Northern from Southern France. It may coincide
with the von Wartburg line, which
divides France into “Langue d’Oïl” part (influenced by Germanic speaking) and “Langue d’Oc” part (closer to Roman
speaking). This border has changed through centuries and our North-South limit
is close to the limit as it was estimated in the IXth
century. This border also follows the Loire River, which has long been a
political and cultural border between kingdoms/counties in the
North and in the South. Regions with strong cultural particularities tend to
separate. This is for example the case for Aquitaine
in the South-West which duchy has long represented a civilization on its own.
The Brittany region is also detected as a separate entity in both datasets.
This could be explained both by its position at the end of the continent where
it forms a peninsula and, by its history since
Brittany has been an independent political entity (Kingdom and, later, duchy of
Bretagne), with stable borders, for a long time.
extreme South-West regions show the highest differentiation to neighbor
clusters. . . . This cluster is likely due to a higher proportion of
possibly Basque individuals . . . . which overlap with HGDP Basque defined individuals. The FST between the south-west and the other French clusters were
markedly higher than the FST between remaining French
clusters. . . . [T]hese values are comparable to
what we observed between the Italian and the British heritage clusters (FST=0.0035). . . . We also
observe that the broad-scale genetic structure of France strikingly aligns with
two major rivers of France “La Garonne” and “La Loire”. At a
finer-scale, the “Adour” river partition the SW to the SO cluster. . . .
historical, cultural and political borders seem to have shaped the genetic
structure of modern-days France, exhibiting visible clusters, the population is
quite homogeneous with low FST values between-clusters . . . . We find that each cluster
is genetically close to the closest neighbor European country, which is in line
with a continuous gene flow at the European level. However, we observe that
Brittany is substantially closer to British Isles population than North of
France, in spite of both being equally geographically close. Migration of
Britons in what was at the time Armorica (and is now Brittany) may explain this
closeness. These migrations may have been quite constant during centuries
although a two waves model is generally
assumed. A first wave would have occurred in the Xth century when soldiers
from British Isles were sent to Armorica whereas the second wave consisted of
Britons escaping the Anglo-Saxon invasions. . . .
the evolution of French population size based on genetic data, we observe a
very rapid increase in the last generations. This observation is in
line with what has been seen in European populations. We also observe, in most cases, a depression during a
period spanning from 12 to 22 generations ago. This
may correspond to a period spanning from 1300 to 1700. Indeed, this period was characterized by a deep depression in
population size due to a long series of plague events. While the population
size in kingdom of France was estimated to be 20 million in 1348, it dropped
down to 12,415 million in 1400, followed
by an uneven trajectory to recover the 20 million at the end of Louis XIVth reign (1715). However, the decrease we observe in the
genetic data does seem to affect mainly the Northern part of France, and for
instance is mainly observed in the NO cluster. We see no reason for this trend
based on historical records except perhaps the last plague epidemics in 1666-1670
that was limited to the North of France. Alternatively, a more spread
population in the South (which is in general hilly or mountainous) may explain
a lower impact of these dramatic episodes.
Plague is expected to have had a very strong impact on the population
demography in the past as some epidemics led to substantial reduction in the
Thus, in a nutshell, Northern France is more Germanic, Brittany is more Celtic, the far southwest corner of France looks Basque. the core of "yellow" component France in modern populations shown in the study result map above correspond to the historic Kingdom of Aquitaine. The population segment in the Southeast of France above is very similar to the Tuscan population of Italy sample
in the 1000 Genomes Project study.
The demographic impact of the Black Plague on French population genetics is apparent and the highlands were less hard hit by the plague than the lowlands were.
Southwest French descend from the ancient Aquiatine who Ceasar noted were a distinct nation from the Gauls. Aquiatine were Basque, hence Southwest French are identical to Basque in Spain.
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