Continental Persistence of Y-DNA Haplogroup R-Z251 and Matrilocal Filtering in the Iron Age Arras Culture: Testing the Insular Back-Migration Model Through Multi-Corridor Riverine Phylogeography (R-S9294, R-FGC11986, R-Z16943, R-FGC13899), the August 2026 East Yorkshire Dataset, and Ten Akbari et al. (2026) Twist-Capture Genomes

Abstract: Because commercial Y-DNA databases are heavily skewed toward testers of British Isles and colonial American descent, Continental European subclades under R-L21 > R-DF13 > R-Z251 are routinely dismissed as isolated medieval back-migrations from Britain. This paper tests that paradigm against the ancient record and finds it unsupported in its strong form, while declining to replace it with an equally strong Continental claim. R-L21 descends from R-L151 men whose Bronze Age burials are overwhelmingly Continental, so Continental ancestry is the shared starting condition of the entire haplogroup rather than an anomaly requiring special explanation; what is at issue is only the date at which a given sub-lineage crossed. Within that frame the paper argues for Continental persistence at low frequency rather than a demographically dominant reservoir, and traces R-Z251 (and downstream R-S9294 > R-FGC11998 > R-FGC11986) along five distinct hydrographic corridors radiating from the triple-watershed divide of the Plateau de Langres in eastern Gaul: (1) R-FGC11998 > R-BY150334 along the Seine–Marne corridor to Paris and across the Channel to East Yorkshire; (2) R-Z16943 > R-FGC56332 along the Meuse–Belgic corridor into West Sussex (North Bersted I27379); (3) R-BY3226 / Z18106 > R-A555 (Ashkenazi Branch AB-078) along the Rhine–Main corridor into the Vistula basin in Poland; (4) R-BY9004 > R-BY54802 along the lower Rhine into Lower Saxony and Denmark; and (5) R-FGC13899 > R-A228 along the Rhine–Moselle corridor into Germany. Second, using the August 2026 East Yorkshire Arras Culture dataset (534 genomes; Olalde, Armit et al., 2026) and ten newly analyzed Twist-capture genomes from Akbari et al. (2026)—including a second Hallstatt-era R-S9294 anchor (I35050.TW, 600 BCE) and three La Tène samples converging on Faux-Vesigneul in the Marne (I36184.TW, I35763.TW, I28725.TW)—this study shows how matrilocal female endogamy in Iron Age Britain diluted the Continental autosomal signal of incoming Gaulish male founders below qpAdm detection limits (<= 6%) within four generations while preserving their Y-DNA intact, resolving the long-standing Parisi/Parisii archaeological paradox. Third, a direct frequency test against the Allen Ancient DNA Resource (v66.0) establishes that twenty R-Z251 individuals occur among 206 determinable East Yorkshire males (9.7%), against 1.0% in non-Arras Iron Age Britain, 1.0% in Continental Iron Age northwestern Europe and 0.05% across the entire 10,099-male corpus (odds ratio 11.1 against the British Iron Age baseline, p = 0.003); eleven of the twenty carry the two dominant Wetwang matrilines, and all thirteen called at Wetwang Slack fall within a single within-site diversity group with ten of fourteen having first- to third-degree relatives on site, so the East Yorkshire occurrences represent one closely