Originally Posted by
Philip Latinowitz
According to Eupedia I2 seem to be Slavic haplogroup after all:
The high concentration of I2a1b-L621 in north-east Romania, Moldova and central Ukraine reminds of the maximum spread of the Cucuteni-Trypillian culture (4800-3000 BCE). No Y-DNA sample from this culture has been tested to date, but as it evolved as an offshoot from the Starčevo–Kőrös–Criş culture, it is likely that I2a was one of its main paternal lineages, and a founder effect could have increased considerably its frequency. The Cucuteni-Trypillian culture was the most advanced Neolithic culture in Europe before the Indo-European invasions in the Bronze Age and seems to have had intensive contacts with the Steppe culture before the expansion of Yamna to the Balkans and Central Europe (see histories of R1a and R1b). From 3500 BCE, at the onset of the Yamna period in the Pontic-Caspian Steppe, the Cucuteni-Trypillian people started expanding east into the steppe of what is now western Ukraine, leaving their towns (the largest in the world at the time), and adopting an increasingly nomadic lifestyle like their Yamna neighbours. It can easily be imagined that Cucuteni-Trypillian people became assimilated by the Yamna neighbours and that they spread as a minority lineage alongside haplogroups R1a and R1b as they advanced toward the Baltic with the Corded Ware expansion. Alternatively, I2-L621 lineages could have lived in relative isolation from the mainstream Proto-Indo-European society somewhere around Ukraine, Poland or Belarus, then as the centuries and millennia passed, would have blended with the predominantly R1a populations around them. The resulting amalgam would have become the ancestors of the Proto-Slavs.
The I2a1b-L147.2 subclade seems to have expanded very fast from 1900 years ago, which is concordant with the timing of the Slavic ethnogenesis, considering that it takes a few centuries before one man can have enough male descendants to start having an impact at the scale of a (small but fast-growing) population.
Nowadays northern Slavic countries have between 9% (Poland, Czech republic) and 21% (Ukraine) of I2a-L621, while southern Slavs have between 20% (Bulgaria) and 50% (Bosnia). The higher percentage of I2a-Din in the south is probably just due to another founder effect due to the fact that the South Slavs originated in western Ukraine, where the ratio of I2a to R1a was higher. Virtually all Dinaric I2a falls under the CTS10228 (aka CTS5966 or L147.2) subclade, and the majority to the S17250 ramification, who descend from a common patrilinear ancestor who lived only 1,800 years ago.
IDK for credible is this, but sound fairly decent explanation.
