The Source Book (1)

Eastern European hunter-gatherers, with some influences from the
languages of Caucasus hunter-gatherers. Anthony rejects the possibility
that the Bronze Age Maykop people of the Caucasus were a southern
source of language and genetics of Indo-European.[31][32] Referring to
Wang et al. (2019), he notes that the Anatolian Farmer component in
the Yamnaya-ancestry came from European farmers, not from the
Maykop, which had too much Anatolian farmer ancestry to be ancestral
to the Yamnaya-population.[105] Anthony also notes that the paternal
lineages of the Yamnaya, which were rich in R1b, were related to those
of earlier Eastern European hunter-gatherers, rather than those of
southern or Caucasus peoples such as the Maykop.[106] Anthony rejects
the possibility that the Bronze Age Maykop people of the Caucasus
were a southern source of language and genetics of Indo-European.
According to Anthony, referring to Wang et al. (2019),[note 17] the
Maykop culture had little genetic impact on the Yamnaya, whose
paternal lineages were found to differ from those found in Maykop
remains, but were instead related to those of earlier Eastern European
hunter-gatherers. Also, the Maykop (and other contemporary Caucasus
samples), along with CHG from this date, had significant Anatolian
Farmer ancestry "which had spread into the Caucasus from the west
after about 5000 BC", while the Yamnaya had a lower percentage which
does not fit with a Maykop origin. Partly for these reasons, Anthony
concludes that Bronze Age Caucasus groups such as the Maykop
"played only a minor role, if any, in the formation of Yamnaya
ancestry." According to Anthony, the roots of Proto-Indo-European
(archaic or proto-proto-Indo-European) were mainly in the steppe
rather than the south. Anthony considers it likely that the Maykop
spoke a Northern Caucasian language not ancestral to Indo-
European.[31][32][31]