Origins
The TMRCA (time to most recent common ancestor) for the I clade was estimated by Karafet and colleagues in 2008 as 22.2 k.a. (22,200 years ago) with a confidence interval between 15.3-30.0 ka., placing the Haplogroup I-M170 founding event approximately contemporaneous with the Last Glacial Maximum (LGM) which lasted from 26.5 ka to 19 or 20 ka.
The TMRCA is an estimate of the time of subclade divergence. Rootsi and colleagues in 2004 also note two other dates for a clade, age of STR variation, and time since population divergence. These last two dates are roughly associated, and occur somewhat after subclade divergence. For Haplogroup I-M170 they estimate time to STR variation as 24±7.1 ky and time to population divergence as 23±7.7 ky. These estimates are consistent with those of Karafet 2008 cited above. However Underhill and his colleagues calculate the time to subclade divergence of I1 and I2 to be 28.4±5.1 ky, though they calculate the STR variation age of I1 at only 8.1±1.5 kya.
Some speculate the initial dispersion of this population corresponds to the diffusion of the Gravettian culture. Rootsi and colleagues in 2004 suggested that each of the ancestral populations now dominated by a particular subclade of Haplogroup I-M170 experienced an independent population expansion immediately after the last glacial maximum.
Read more about this topic: Haplogroup I (Y-DNA)
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