According to a new study:
We estimate that the geographic origin of hg G plausibly locates somewhere nearby eastern Anatolia, Armenia or western Iran. The general frequency pattern of hg G overall shows that the spread of hg G extends over an area from southern Europe to the Near/Middle East and the Caucasus, but then decreases rapidly toward southern and Central Asia. . . .
Concerning the presence of hg G in the Caucasus, one of its distinguishing features is lower haplogroup diversity in numerous populations compared with Anatolia and Armenia, implying that hg G is intrusive in the Caucasus rather than autochthonous.
Another notable feature is its uneven distribution. Hg G is very frequent in NW Caucasus and South Caucasus, covering about 45% of the paternal lineages in both regions2 in this study. Conversely, hg G is present in Northeast Caucasus only at an average frequency of 5% (range 0–19%). Interestingly, the decrease of hg G frequency towards the eastern European populations inhabiting the area adjacent to NW Caucasus, such as southern Russians and Ukrainians, is very rapid and the borderline very sharp, indicating that gene flow from the Caucasus in the northern direction has been negligible.The paper's methodology is generally reliable. It traces the phylogenetic relationships of subhaplogroups of Y-DNA haplogroup G and then examines the geography of each with an eye towards analytically determining the kind of pattern of distribution that could produce that result.