Overview
Haplogroup R-PH155 is an early and rare branch of R1b that diverged directly from the basal node R-L278. In modern phylogenetic schemes it is often classified as R1b2, in contrast to the much larger R1b1a cluster that includes R-P297 and R-M269. PH155 therefore represents an alternative evolutionary path within R1b, one that did not undergo the same massive demographic expansion but instead remained numerically modest and regionally constrained.
The geographic and temporal context of PH155 places its early diversification somewhere in western Asia or adjacent parts of eastern Europe and the Caucasus, during the late Upper Paleolithic and early Holocene. As human groups adapted to changing post glacial environments, carriers of PH155 likely formed part of small, regionally stable populations that contributed only limited paternal lineages to later historic groups. Their descendants appear today at low frequencies, mostly in parts of the Near East, the Caucasus and neighboring regions.
Because PH155 is rare and often overshadowed in datasets by the much more common R-M269 and R-V88 lineages, its demographic history is still being clarified. However, its position directly under L278 and its survival into the present make it a crucial piece of evidence for understanding how many independent R1b branches persisted through the Holocene, even if only some of them experienced large scale expansions.
Geographic distribution
Modern R-PH155 lineages are sparse but have been reported in western Asia, including Iran and neighboring regions, as well as in parts of the Caucasus and the eastern Mediterranean. Frequencies are typically low, and most populations show only isolated occurrences.
Ancient DNA
- Ancient DNA data for PH155 are still limited, but its time depth indicates that early PH155 lineages would have been present among late Upper Paleolithic and early Holocene populations in western Asia or the Caucasus.
- Some ancient individuals classified simply as basal R1b or R1b* in older studies may in fact belong to PH155 or closely related branches once reanalyzed with modern SNP panels.
- The rarity of PH155 in both modern and ancient material suggests that it never participated in major Neolithic or Bronze Age founder events, in contrast to R-M269 and R-V88.
Phylogeny & subclades
R-PH155 is one of the two main branches arising from the basal node R-L278, the other being R-L754. While L754 leads to the large radiations that dominate western Eurasian R1b, PH155 represents an alternative branch with limited expansion. Its internal substructure is still being refined as more high coverage Y chromosome data become available.
- R-PH155* (basal lineages)
- Several very small downstream clusters with Near Eastern and Caucasus distributions
Notes & context
R-PH155 is a key lineage for illustrating that R1b was never a single homogeneous expansion but rather a set of parallel branches with very different demographic outcomes. Including PH155 in the atlas ensures that the full early diversity of R1b is represented, not only its dominant M269 centered branches.
References & external links