Overview
Haplogroup I2 is the major descendant branch of haplogroup I that preserves most of the deep diversity associated with European hunter gatherers. Defined by P215 and related markers, it diverged from the I trunk during the Upper Paleolithic and became the dominant paternal lineage of Mesolithic western, central and southeastern Europe. In many Mesolithic sites, especially in the Balkans and central Europe, almost all male individuals belong to I2 derived lineages, which makes I2 the key Y chromosome clade for reconstructing pre Neolithic European ancestry.
The internal structure of I2 reveals multiple refugial and postglacial expansion centers. Branches rooted in southeastern Europe and the Adriatic corridor, in the Carpathians and in parts of the Ukrainian steppe participated in the recolonization of northern and western Europe after the Last Glacial Maximum. Later, during the Neolithic, I2 lineages admixed with incoming Near Eastern farmer lineages such as G2a and J, producing mixed populations in which I2 remained an important paternal component. In the Bronze Age and Iron Age, additional movements, including steppe related expansions, reshaped the frequencies and distributions of I2, but many of its subclades persisted and can be detected in modern populations.
Geographic distribution
Modern I2 is most frequent in southeastern and central Europe. High peak values occur in the western Balkans (Bosnia and Herzegovina, Croatia, Serbia, Montenegro), in the Dinaric Alps, in parts of Romania and in the Carpathian region. Additional concentrations are found in Ukraine, Moldova and parts of Poland, as well as in Sardinia, where specific I2a lineages have been preserved at elevated frequencies.
Lower but still meaningful frequencies of I2 occur throughout much of Europe, including Italy, France, Germany, the British Isles and Scandinavia, usually as a legacy of Mesolithic and early Neolithic ancestry overlain by later demographic layers. Outside Europe, I2 is present at low frequencies in the Near East and the Caucasus, often reflecting either back migrations from Europe or ancient contact zones in the Balkans and Black Sea region.
Ancient DNA
- Mesolithic hunter gatherer individuals from western, central and southeastern Europe overwhelmingly belong to I2 derived lineages, particularly in the Balkans, the Iron Gates region and central European forest steppe zones.
- Early and Middle Neolithic European farmers, whose primary paternal ancestry is Near Eastern derived, still show a substantial minority of I2 males, indicating admixture between incoming farmers and local foragers.
- Later Neolithic and Chalcolithic samples from the Carpathian Basin, the Balkans and the Mediterranean continue to show I2, although its relative frequency declines in some regions as other haplogroups expand.
- Bronze Age and Iron Age European datasets show a patchwork of I2 branches, confirming its long term persistence through multiple cultural and demographic transitions.
Phylogeny & subclades
Within haplogroup I, I2 sits as a sister branch to I1 and retains a much older and more complex set of internal radiations. At a high level, I2 can be divided into I2a and I2b (and several rare minor branches), which together cover the bulk of its diversity. I2a contains many of the lineages associated with Balkan, Carpathian, Sardinian and Ukrainian hunter gatherers and later farmer forager hybrids, while I2b contains western and central European branches that once formed part of the Mesolithic and early Neolithic paternal landscape in those regions.
For an atlas, modeling I2 as a separate node above I2a and I2b allows users to distinguish between Mesolithic ancestry in general and specific regionally focused radiations that follow.
- I2a – southeastern and central European radiations
- I2b – western and central European and Balkan associated branches
- rare minor I2 lineages
Notes & context
I2 is arguably the single most important haplogroup for understanding indigenous European paternal ancestry before the arrival of Near Eastern farmers and steppe associated groups. Its many regionally distinct branches provide a fine grained record of European postglacial recolonization and subsequent admixture events.
References & external links