Overview
I2b3 is a rare but phylogenetically meaningful branch within the I2b complex that groups a set of residual western European Mesolithic derived lineages. These lineages survived at very low frequencies through the Neolithic and Bronze Age, often in marginal or upland regions where local continuity persisted despite major demographic turnovers elsewhere. In modern datasets, I2b3 appears as scattered microclusters with deep divergence times and limited internal branching, typical of lineages that escaped both extinction and major expansion.
By definition, I2b3 is an atlas oriented grouping for those I2b chromosomes that do not fall neatly into the more clearly structured I2b1 and I2b2 lineages but show western or northwestern European affinities. Their presence highlights the incomplete nature of our sampling of Mesolithic paternal ancestry and the likelihood that additional rare branches once existed in greater diversity.
Geographic distribution
I2b3 is found in small numbers across western Europe, including France, the Low Countries, western Germany and occasionally the Iberian Peninsula. Low frequency occurrences also appear in the British Isles and in some coastal Atlantic regions. In central and eastern Europe, I2b3 is very rare.
The pattern suggests that I2b3 lineages persisted in localized western European communities that were only weakly impacted by later expansions, or that they survived as minor components within mixed populations formed after these expansions.
Ancient DNA
- Some low coverage Mesolithic and Neolithic western European individuals show I2b like markers that may represent ancestral forms of I2b3.
- Due to the rarity of this branch and the limitations of ancient coverage, few securely assigned I2b3 ancient genomes have been reported, but the geographic and phylogenetic patterns are consistent with a western Mesolithic origin.
- Where present, I2b3 related signatures in later prehistoric and historic individuals point to continuity of small local paternal lines.
Phylogeny & subclades
I2b3 occupies a marginal position within the I2b tree, branching off from the trunk at a similar depth to I2b1 and I2b2 but never attaining the same demographic weight. Its internal phylogeny is characterized by a handful of deeply split microbranches, many represented by very few modern samples. For atlas purposes, I2b3 functions as a schematic cluster summarizing these residual western lineages.
- I2b3* basal western residual lineages
- I2b3a – Atlantic fringe microbranches
Notes & context
I2b3 illustrates how not all Mesolithic derived lineages expanded or disappeared completely. Some persisted quietly in small communities and are only now being detected by high resolution sequencing. Including such a branch in the atlas preserves the complexity of the I2b radiation and avoids presenting an overly simplified picture of European prehistory.
References & external links