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.
[2], placing the
Haplogroup I founding event approximately contemporaneous with the Last Glacial Maximum (LGM) which lasted from 26.5 ka to 19 or 20 ka.[3]
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 they estimate time to STR variation as 24±7.1 ky and time to population divergence as 23±7.7 ky.
[4] 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.
[5]
Some speculate the initial dispersion of this population corresponds to the diffusion of the
Gravettian culture.
[6] Rootsi and colleagues in 2004 suggested that each of the ancestral populations now dominated by a particular subclade of Haplogroup I experienced an independent population
expansion immediately after the last glacial maximum.[4]