I don't really understand why there is such a heated argument about the origins of the Anatolian branch. Some people seem to think that it is important to determine whether PIE originated in the Steppe or in the South Caucasus. But that's a false dichotomy. I have been saying for nearly 10 years, without needing to adjust my discourse as all ancient DNA evidence have always confirmed my proposed scenario, that R1b-M269 (and L23, which was not yet discovered when I started writing my R1b history in early 2009) originated in the South Caucasus (or Eastern Anatolia, which is almost the same thing) and that this R1b branch were cattle herders who crossed the Caucasus between 6000 and 5000 BCE. They mixed with the local population (I2a, R1a and, to my surprise also older branches of R1b like L388 and P297), and only then around the time of the Late Khvalynsk/Sredny Stog or Early Yamna/Maykop can we say that a common lingua franca had appeared in the Pontic Steppe that included vocabulary for horses (domesticated c. 4000 BCE), carts/wagons and metallurgy.
I have explained
here and
here why it is nonsensical to think of the Hittites and other Anatolian IE as not having a Steppe origin. They had Steppe vocabulary and even possessed Steppe technology. There is no way these people were descendants from the R1b-L23 who stayed in the South Caucasus. Since PIE is estimated to be approximately 6000 years old (4000 BCE), it is equally ludicrous to believe that the Anatolian branch could have split from other IE languages 8000 years ago. Yet one cannot say that the Anatolian branch remained in the Caucasus without asserting all this by the same occasion.
As for the CHG admixture in Bronze Age Anatolia, most of it would have been brought by the
Kura-Araxes expansion, which was contemporaneous to the Yamna expansion, but from the South Caucasus to Anatolia, Aegean Greece, Cyprus, the Fertile Crescent, Iran, Bactria-Margiana and as far as the Indus. The Hurrians, Hattians, Minoans, and possibly also the Akkadians, Assyrians and Elamites descend at least partly from the Kura-Araxes people. The Kura-Araxes haplogroups included J2a1 (M319, Z7671, F3133, Z6046, L581, etc.), J1-Z1828, G2a-L293 and T1a-P77.
But the bottom line is that R1b-L23 is the principal original lineage of PIE, as R1b-L23 did originated in the South Caucasus, but PIE as a language did not develop until c. 4000 BCE over 1000 to 2000 years after R1b-L23 settled in the Pontic Steppe.
So genetically, the paternal line of Indo-European is from the South Caucasus, but PIE people and language are a hybrid of South Caucasian and Steppe people. There is no point arguing beyond that.