Overview
I3 represents one of the rarest but most phylogenetically important branches of the I macro-haplogroup. It diverged shortly after the initial structuring of the paternal lineages that would become I1, I2 and their numerous subbranches. I3 likely originated among late Upper Paleolithic West Eurasian foragers inhabiting the zones between Anatolia, the southern Caucasus and the northern Levant. Its deep divergence and minimal modern representation indicate that it once formed part of a larger early West Eurasian paternal diversity that did not survive into the present at high frequencies.
The existence of I3 helps illuminate the early fragmentation of West Eurasian paternal lineages following the Last Glacial Maximum. Because I3 sits near the basal branches of haplogroup I, it is essential for reconstructing the earliest phases of the European and Near Eastern prehistory before the expansions of Mesolithic and Neolithic populations reshaped the paternal landscape.
Geographic distribution
Modern I3 lineages are extremely rare. Most confirmed cases derive from Armenia, Georgia, eastern Turkey and northern Iran. Occasional occurrences are reported in the Levant and southeastern Europe. Very low-frequency instances in Europe generally reflect ancient but highly drifted lineages or incomplete marker testing.
I3 is virtually absent in diaspora populations outside Eurasia except through recent migration from these regions.
Ancient DNA
- No securely assigned high-coverage I3 ancient genomes exist yet, but several Upper Paleolithic and early Holocene Near Eastern individuals show upstream signals compatible with basal I positions that could fall on the I3 stem.
- Genomic modeling of early Anatolia–Caucasus corridors suggests that rare I3-like lineages may have contributed minimally to CHG and Anatolian hunter-gatherer ancestries.
- Its survival into the present in tiny pockets supports the idea that I3 once had a wider Paleolithic distribution.
Phylogeny & subclades
I3 divides into two principal downstream branches within atlas modeling: I3a and I3b. This structure captures the deep Paleolithic fragmentation and later minor survival of these lineages in the Armenian Highlands, Zagros fringe and Caucasus piedmont.
- I3a – Anatolia–Caucasus derived branch
- I3b – northern Zagros and Iranian Plateau oriented branch
Notes & context
I3 is one of the most important rare lineages for understanding the earliest phases of haplogroup I diversification. Its scarcity today is part of its significance.
References & external links