North Caucasian genetics - The source of Steppe ancestry

Let's discuss the origins of Steppe ancestry in North West Caucasian ( NWC) people also known as Abkhaz-Adyghean family. Here is a quote from Wang paper.

------ 

First, sometime after the BA present-day North Caucasian populations must have received additional gene-flow from steppe populations that now separates them from southern Caucasians, who largely retained the BA ancestry profile. The archaeological and historic records suggest numerous incursions during the subsequent Iron Age and Medieval times33, but ancient DNA from these time periods will be needed to test this directly. 

------ 

Indeed we have a Dolmen LBA sample which do not have steppe ancestry despite the fact that it is a prime candidate of being Proto NWC culture. Modern NWC do have steppe ancestry (except Abkhazians)  mostly from a Scythian source, this after LBA. The presence of R1a in NWC reinforce this idea. Also they have East Asian ancestry from medieval Turkic populations. In the picture attached it is called MNG_Early_Xiongnu. And some minor Yamna related ancestry which is called Kubano-Tersk. The low level of direct Yamna ancestry in North West Caucasus is not surprising given that R1b Z2103 is less frequent than R1a Abkhaz-Adyghean people. Interestingly NWC people do not have any ancestry from Steppe Maykop, which should not be confused with Mountainous (Caucasus) Maykop.

Most ancestry in NWC people is from MBA North Caucasus sample from Kudachurt. It has virtually no Steppe ancestry, and genome wide it is close to Eneolithic period Darkveti Meshoko. I couldn't use Dolmen LBA because it is absent in the G25 calculator. In most likelihood the extra Anatolian farmers related ancestry (Bulgaria_Chl) that NWC people had is related to Bronze Age Dolmen culture. The alternative explanation is the Colchian culture. The extra Anatolian shift could be related to high level of G2a2b in North West Caucasus. What is the origin of Y dna G2a2-U1>L1264 prevalent in NWC people is not clear but ancient DNA almost certainly will help to solve this puzzle.