A Breton is genetically closer to a Welshman than to someone from Provence. An Alsatian shares more common ancestors with a German than with a Corsican. These realities, revealed by G25 coordinate analysis, remind us of a historical truth: modern political borders are recent constructions that have never stopped millennia-old genetic flows.
Key Finding
The genetic distance between someone from Finistère (Brittany) and a Welshman is up to 6.5 times smaller than between that same Breton and someone from Provence. The English Channel has never been a genetic border.
Genetics Ignores Passports
When we speak of "French genetics" or "German genetics," we commit a fundamental anachronism. These nations have only existed in their current form for a few centuries, a blink of an eye on the scale of human genetic history. The populations inhabiting these territories today are the product of millennia of exchanges, migrations, marriages, and conquests that never respected the lines drawn on our modern maps.
The analysis of Global25 (G25) coordinates, developed by David Wesolowski, offers us a powerful tool for visualizing these realities. By reducing the human genome to 25 principal components, G25 allows us to compare populations across space and time with remarkable precision.
France: A Genetic Crossroads of Europe
France occupies a unique geographical position in Western Europe, at the intersection of multiple genetic influences. This position is reflected in remarkable internal genetic variation, far greater than political borders might suggest.
A Breton is 6.5 times closer to a Welshman than to a Provençal
G25 Distance Finistère → Wales
G25 Distance Finistère → Provence
Our analyses of French departmental averages reveal fascinating patterns. Northwestern French departments (Brittany, Normandy) form a genetic continuum with British populations. Northeastern departments (Alsace, Nord, Lorraine) cluster with Germanic and Belgian populations. And southwestern departments show marked affinity with Iberian populations.
Northwestern France: A Genetic Extension of the British Isles
The case of Brittany is particularly revealing. Inhabitants of Finistère show remarkable genetic proximity to the Welsh, a proximity explained by millennia of exchanges across the Channel and a shared Celtic heritage.
| Comparison | G25 Distance | Interpretation |
|---|---|---|
| Finistère → Wales | 0.0094 | Very close (same cluster) |
| Finistère → Ireland | 0.0132 | Very close |
| Finistère → England | 0.0085 | Close |
| Finistère → Provence | 0.0612 | More distant (different cluster) |
| Finistère → Corsica | 0.0682 | Very distant |
These data demonstrate a counter-intuitive reality for many: the English Channel has never been a genetic border. This narrow strait has been, on the contrary, a communication route facilitating exchanges between Atlantic populations since the Mesolithic.
"Europe's genetic borders are far older than its political borders. They were shaped by geography, climate, and the great prehistoric migrations, not by diplomatic treaties of the 19th century." , Iain Mathieson, geneticist at the University of Pennsylvania
Northeastern France: A Germanic Continuum
At the other end of the Hexagon, northeastern departments show marked genetic affinity with Germanic populations. Alsace, in particular, presents G25 coordinates very close to those of southwestern Germans.
Closer across borders
Alsace → Germany: 0.0248
Nord → Belgium: 0.0097
Moselle → Luxembourg: 0.0063
More distant within France
Alsace → Provence: 0.0289
Nord → Corsica: 0.0612
Moselle → Pyrénées-O.: 0.0445
The Rhine, often presented as a "natural" border in French history books, has never constituted a genetic barrier. Populations on both banks share a common genetic heritage, inherited from the same successive migration waves since the Neolithic.
The Real Genetic Borders: Alps and Pyrenees
If the Channel and the Rhine don't constitute genetic borders, which geographical barriers have actually influenced European genetic distribution? The answer lies in the mountain ranges.
The Alps: A Real Genetic Border
Unlike rivers and seas, the Alps have effectively limited genetic flows between northern and southern European populations. The genetic difference between someone from Savoy and an inhabitant of Italian Piedmont is significantly greater than that between a Breton and a Welshman, despite the presence of the Channel.
This reality is explained by the historical difficulty of crossing Alpine passes, particularly in winter. While the Channel could be crossed in a few hours in good weather, crossing the Alps represented a journey of several days, dangerous and often deadly.
The Pyrenees: A Partial Barrier
The Pyrenees also constitute a genetic border, but less pronounced than the Alps. Populations on the French and Spanish slopes show measurable differences, while maintaining relative proximity, particularly in traditional passage areas like the Basque Country and Catalonia.
Exceptions That Prove the Rule
The Basques: A Persistent Mystery
The Basques represent one of the most distinctive populations in Western Europe. With a genetic distance of 0.0289 from the French average, nearly 12 times the Finistère-Wales distance, they form a remarkable genetic isolate.
This uniqueness is partly explained by their isolation in the Pyrenean valleys, but also by an exceptional genetic continuity with pre-Indo-European populations of Western Europe. The Basques have retained a higher proportion of Neolithic farmer and Mesolithic hunter-gatherer ancestors than their neighbors.
The Sardinians: Heirs of the Neolithic
Even more distinct than the Basques, the Sardinians represent the modern European population genetically closest to the first Neolithic farmers. With a distance of 0.1178 from the French average, the Sardinians constitute a true genetic "living fossil."
This unique position is explained by Sardinia's insular isolation, which preserved the population from the great migration waves that reshaped the rest of Europe, notably the steppe migrations of the Bronze Age.
What This Means for Your DNA Test
If you've taken a commercial DNA test, these realities explain why your results may seem surprising. A French person of Breton ancestry may see a significant "British" component in their results, not because they have an unknown English ancestor, but because Bretons and Britons share common ancestors and testing companies' algorithms struggle to distinguish these genetically close populations.
Similarly, an Alsatian may get a significant "German" component, and an inhabitant of Pyrénées-Orientales an "Iberian" component. These results are not errors: they reflect genetic realities that modern political borders cannot erase.
Understanding Your DNA Results
If you're from northwestern France and your test shows a British component, that's normal. If you're from the northeast and it shows a Germanic component, that's expected. DNA tests don't measure nationalities, they measure genetic proximities that ignore borders.
Visualizing Gradients with G25
The G25 system allows precise quantification of these genetic proximities. Here are some average coordinates you can use in Vahaduo to explore these continuums yourself:
G25 Coordinates for Vahaduo
Conclusion: Rethinking Our Vision of Nations
Genetic data invites us to healthy humility when facing modern political and identity constructions. European nations as we know them are recent creations, a few centuries at most, while the populations inhabiting them are the product of tens of thousands of years of exchanges, migrations, and mixing.
A "French person" doesn't exist genetically as a homogeneous and distinct category. What exists are continuous gradients of genetic variation that cheerfully cross modern borders, linking the Breton to the Welshman, the Alsatian to the German, the French Catalan to their Spanish neighbor.
This reality, far from denying cultural and national identities, enriches them by placing them in their true historical context: that of a Europe that has always been a space of circulation and exchange, where genes, like ideas and goods, have never really known borders.
References and Sources
- Lazaridis, I. et al. (2022). "The genetic history of the Southern Arc: A bridge between West Asia and Europe." Science. DOI: 10.1126/science.abm4247
- Olalde, I. et al. (2019). "The genomic history of the Iberian Peninsula over the past 8000 years." Science. DOI: 10.1126/science.aav4040
- Patterson, N. et al. (2022). "Large-scale migration into Britain during the Middle to Late Bronze Age." Nature. DOI: 10.1038/s41586-021-04287-4
- Brunel, S. et al. (2020). "Ancient genomes from present-day France unveil 7,000 years of its demographic history." PNAS. DOI: 10.1073/pnas.1918034117
- Marcus, J.H. et al. (2020). "Genetic history from the Middle Neolithic to present on the Mediterranean island of Sardinia." Nature Communications. DOI: 10.1038/s41467-020-14523-6
- Wesolowski, D. (2023). "Global25 coordinates." Eurogenes Blog & G25 Vahaduo.
- Moriopoulos Collection (2025). "Modern population G25 averages." Compiled data.