Older research considered that the high frequency of this subclade (I2a-L621) in the South Slavic-speaking populations to be the result of "pre-Slavic" paleolithic settlement in the region. Peričić et al. (2005) for instance place its expansion to have occurred "not earlier than the YD to Holocene transition and not later than the early Neolithic".
However the prehistoric autochthonous origin of the haplogroup I2 in the Balkans is now considered as out of date,[nb 1] as already Battaglia et al. (2009) observed highest variance of the haplogroup in Ukraine, and Zupan et al. (2013) noted that it suggests it arrived with Slavic migration from the homeland which was in present-day Ukraine.