H45B

Origins and Evolution

H45B is a low-frequency mitochondrial subclade derived from H45, which in turn branches from the broader H4 lineage. Based on the phylogenetic position of H45 and the geographic focus of sampled carriers, H45B most likely arose on the Iberian/Atlantic fringe after the main Neolithic expansions, during the later Neolithic to Bronze Age transition (roughly ~4.5 kya). Its emergence is consistent with the pattern of regional diversification of H subclades in western Europe following post-glacial recolonization and subsequent local demographic processes.

Genetically, H45B is defined by a small set of derived mutations on top of the H45 motif; because it is rare, full resolution of its internal branching is limited and relies on few complete mitogenomes. The scarcity of high-coverage ancient and modern whole-mtDNA sequences assigned to H45B constrains precise coalescent dating, but its placement as a younger daughter of H45 allows a reasonable inference of a mid-Holocene origin concentrated on the Atlantic margin.

Subclades

At present, H45B is a shallow, low-diversity clade with no widely recognized, deeply branching subclades in public phylogenies — most available samples fall directly under the H45B node. Continued mitogenome sequencing of understudied Atlantic populations may reveal further internal structure, but currently H45B should be treated as a rare terminal/near-terminal branch within H45.

Geographical Distribution

The geographic signal for H45B mirrors that of its parent but at reduced frequency. Modern observations and inferred historical distributions place most carriers in:

• Iberia (Spain and Portugal), including occasional representation in Basque-speaking groups, where Atlantic H lineages are most concentrated.
• Atlantic France (Brittany and adjacent coasts), consistent with maritime and coastal population continuity.
• British Isles (England, Scotland, Ireland) at very low frequencies, likely reflecting prehistoric and historic maritime links across the Atlantic shelf.
• Southern Europe (limited occurrences in Italy and Sardinia), typically at very low incidence due to later gene flow.
• North Africa and the Near East only sporadically, likely reflecting historical contacts and small-scale bidirectional gene flow across the western Mediterranean.

The haplogroup is rare in all regions and has been identified in only a handful of modern mitogenomes and a very small number of ancient samples, so frequency estimates remain low and geographically patchy.

Historical and Cultural Significance

Because H45B is uncommon, it does not mark a large pan-regional demographic expansion the way major H subclades (e.g., H1 or H3) do. However, its concentration on the Atlantic fringe suggests continuity of maternal lineages in coastal pockets that persisted through the Neolithic and into later prehistoric periods. Possible associations and interpretations include:

• Survival of local maternal lineages that diversified after the Last Glacial Maximum and were incorporated into Neolithic farmer and later coastal Bronze Age communities.
• Maritime and coastal transmission: low-level spread around the Atlantic shelf via coastal mobility and trade, consistent with connections observed in other Atlantic H lineages.
• Archaeological contexts: while H45 (the parent) is occasionally found in Neolithic/Bronze Age ancient DNA, direct ancient attestation of H45B is presently very limited; as ancient mitogenomes increase, H45B may appear more often in regional prehistoric contexts (for example in Atlantic Neolithic or Bronze Age burials).

Overall, H45B is better interpreted as a regional marker of maternal continuity and local differentiation rather than as a signature of a major migration event.

Conclusion

H45B is a rare, regionally focused daughter clade of H45 with an inferred origin on the Iberian/Atlantic fringe in the mid-Holocene (~4.5 kya). Its low diversity and scarcity in both modern and ancient datasets indicate a small effective population size and limited geographic spread, tied to coastal western Europe. Continued targeted mitogenome sequencing of Atlantic populations and increased ancient DNA sampling are the most likely routes to better characterize H45B's internal structure, chronology, and past demographic role.