Apologies if this has already been posted.

See:

I don't see much new. As always, however, he's a very good summarizer and writes very clearly.

I wonder if it's the Reich Lab who asked him to take a look at all the genetic data and try to match it to his knowledge of the archaeological record and the linguistics.

"But before 4500 BC, CHG ancestry appeared among theEHG hunter-fishers in the middle Volga steppes from Samara toSaratov, at the same time that domesticated cattle and sheepgoats appeared. The Reich lab now has whole-genome aDNAdata from more than 30 individuals from three Eneolithiccemeteries in the Volga steppes between the cities of Saratovand Samara (Khlopkov Bugor, Khvalynsk, and Ekaterinovka),all dated around the middle of the fifth millennium BC."

"three Khvalynsk individuals, dated about 4500 BC, showed EHGancestry admixed substantially with CHG, and not a trace ofAnatolian Farmer ancestry, so the CHG was a Hotu-Cave orKotias-Cave type of un-admixed CHG. The proportion of CHGin the Wang et al. (2018) bar graphs is about 20-30% in twoindividuals, substantially less CHG than in Yamnaya; but thethird Khvalynsk individual had more than 50% CHG, likeYamnaya. The ca. 30 additional unpublished individuals fromthree middle Volga Eneolithic cemeteries, including Khvalynsk,preliminarily show the same admixed EHG/CHG ancestry invarying proportions. Most of the males belonged to Ychromosome haplogroup R1b1a, like almost all Yamnaya males,but Khvalynsk also had some minority Y-chromosomehaplogroups (R1a, Q1a, J, I2a2) that do not appear or appearonly rarely (I2a2) in Yamnaya graves."

"Wang et al. (2018) discovered that this middle Volgamating network extended down to the North Caucasiansteppes, where at cemeteries such as Progress-2 andVonyuchka, dated 4300 BC, the same Khvalynsk-type ancestryappeared, an admixture of CHG and EHG with no AnatolianFarmer ancestry, with steppe-derived Y-chromosomehaplogroup R1b. These three individuals in the North Caucasussteppes had higher proportions of CHG, overlapping Yamnaya.Without any doubt, a CHG population that was not admixedwith Anatolian Farmers mated with EHG populations in theVolga steppes and in the North Caucasus steppes before 4500BC. We can refer to this admixture as pre-Yamnaya, because itmakes the best currently known genetic ancestor for EHG/CHGR1b Yamnaya genomes. The Progress-2 individuals from NorthCaucasus steppe graves lived not far from the pre-Maikopfarmers of the Belaya valley, but they did not exchange mates,according to their DNA. The hunter-fisher camps that first appeared on the lowerVolga around 6200 BC could represent the migration northwardof un-admixed CHG hunter-fishers from the steppe parts of thesoutheastern Caucasus, a speculation that awaits confirmationfrom aDNA. After 5000 BC domesticated animals appeared inthese same sites in the lower Volga, and in new ones, and ingrave sacrifices at Khvalynsk and Ekaterinovka. CHG genes anddomesticated animals flowed north up the Volga, and EHGgenes flowed south into the North Caucasus steppes, and thetwo components became admixed. After approximately 4500 BCthe Khvalynsk archaeological culture united the lower andmiddle Volga archaeological sites into one variablearchaeological culture that kept domesticated sheep, goats, andcattle (and possibly horses). In my estimation, Khvalynsk mightrepresent the oldest phase of PIE."

"theEneolithic populations of Dnieper-Donets II type seem to havelimited their mating network to the rich, strategic region theyoccupied, centered on the Rapids. The absence of CHG showsthat they did not mate frequently if at all with the people of theVolga steppes, a surprising but undeniable discovery."

"Also, neither they northe Volga steppe Eneolithic populations showed any AnatolianFarmer ancestry."

"among 48 individuals withwhole-genome aDNA from 16 Neolithic and Copper Agecemeteries in Bulgaria and Romania dated 5800-4300 BC, onlythree showed any ancestry from a steppe mating network(Mathieson et al. 2018). Around 95% of the southeasternEuropean farmer population tested had no steppe relatives overa period of 1500 years. They must have actively avoidedmarriage with steppe people, a rule broken only among the elitetowards the end of the Eneolithic. All three of the steppe-admixed exceptions were from theVarna region (Mathieson et al. 2018). One of them was thefamous “golden man’ at Varna (Krause et al. 2016), Grave 43,whose steppe ancestry was the most doubtful of the three. If hehad steppe ancestry, it was sufficiently distant (five+generations before him) that he was not a statisticallysignificant outlier, but he was displaced in the steppe direction,away from the central values of the majority of typicalAnatolian Farmers at Varna and elsewhere. The other two, atVarna (grave 158, a 5-7-year-old girl) and Smyadovo (grave 29,a male 20-25 years old), were statistically significant outlierswho had recent steppe ancestry (consistent with grandparentsor great-grandparents) of the EHG/CHG Khvalynsk/Progress-2type, not of the Dnieper Rapids EHG/WHG type. Again, this issurprising, because the Volga is much farther away from Varnathan the Dnieper. All three graves were unusually wellequipped with typical Varna pottery and ornaments, and grave43 was spectacularly rich. Steppe people occasionally becamethe parents of children whose local parents belonged to OldEuropean elite families, presumably as the result ofarrangements tied to political and economic negotiations. Butthe children were kept in the tell towns and lived and diedthere. Aside from these three elite-looking Varna-regionindividuals dated 4650-4450 BC (Krause et al. 2016; Mathiesonet al. 2018: Supplementary Materials), the majority of Eneolithicfarmers who lived near the steppe region had no stepperelatives, mirroring the absence of Anatolian Farmer ancestryin Eneolithic steppe cemeteries."

I find some of the following pretty speculative:

"I believe that the Suvorovo-Cernavoda Imovement into the lower Danube valley and the Balkans about4300 BC separated early PIE-speakers (pre-Anatolian) from thesteppe population that stayed behind in the steppes and thatlater developed into late PIE and Yamnaya. This archaeological transition marked the breakdown ofthe mating barrier between steppe and Anatolian Farmermating networks.

After this 4300-4200 BC event, AnatolianFarmer ancestry began to pop up in the steppes. The currently oldest sample with Anatolian Farmer ancestry in the steppes inan individual at Aleksandriya, a Sredni Stog cemetery on theDonets in eastern Ukraine. Sredni Stog has often been discussedas a possible Yamnaya ancestor in Ukraine (Anthony 2007: 239-254). The single published grave is dated about 4000 BC (4045–3974 calBC/ 5215±20 BP/ PSUAMS-2832) and shows 20%Anatolian Farmer ancestry and 80% Khvalynsk-type steppeancestry (CHG&EHG). His Y-chromosome haplogroup wasR1a-Z93, similar to the later Sintashta culture and to South Asian Indo-Aryans, and he is the earliest known sample toshow the genetic adaptation to lactase persistence (I3910T).."

He's on firmer ground here, imo.

"The west-to-east gene flow that began after the 4300-4200 BC collapse could have continued into the Yamnayaperiod. Part of the WHG that Wang et al. (2018) detected inYamnaya genomes could have been picked up in the Dniepervalley, where many Dnieper-Donets individuals had WHGancestry, possibly lessening the necessity for mate exchangeswith Globular Amphorae. Probably, late PIE (Yamnaya) evolved in the same part ofthe steppes—the Volga-Caucasus steppes between the lowerDon, the lower and middle Volga, and the North Caucasuspiedmont—where early PIE evolved, and where appropriateEHG/CHG admixtures and Y-chromosome haplogroups wereseen already in the Eneolithic (without Anatolian Farmer).There have always been archaeologists who argued for anorigin of Yamnaya in the Volga steppes, including Gimbutas(1963), Merpert (1974), and recently Morgunova (2014), whoargued that this was where Repin-type ceramics, an importantearly Yamnaya pottery type, first appeared in dated contextsbefore Yamnaya, about 3600 BC. The genetic evidence isconsistent with Yamnaya EHG/CHG origins in the VolgaCaucasus steppes. Also, if contact with the Maikop culture wasa fundamental cause of the innovations in transport andmetallurgy that defined the Yamnaya culture, then the lowerDon-North Caucasus-lower Volga steppes, closest to the NorthCaucasus, would be where the earliest phase is expected."

" I would still guess that the Darkveti-Meshoko culture andits descendant Maikop culture established the linguisticancestor of the Northwest Caucasian languages inapproximately the region where they remained. I also acceptthe general consensus that the appearance of the hierarchicalMaikop culture about 3600 BC had profound effects on preYamnaya and early Yamnaya steppe cultures. Yamnayametallurgy borrowed from the Maikop culture two-sided molds,tanged daggers, cast shaft hole axes with a single blade, andarsenical copper. Wheeled vehicles might have entered thesteppes through Maikop, revolutionizing steppe economies andmaking Yamnaya pastoral nomadism possible after 3300 BC. So it is still possible that steppe people interacted asraiders and traders and perhaps even political clients of theMaikop people, with interaction intense enough to makeleading political figures in the pre-Yamnaya steppes bilingual inthe Maikop (Northwest Caucasian?) language. Some Maikopwomen might also have become the wives of some preYamnaya men. If their speech was copied by others aroundthem, the linguistic exchanges and interferences suggested byBomhard could have occurred and spread without an equallylarge exchange of mates. But if the interpretations presentedhere are supported, mate exchanges between Maikop and preYamnaya or Yamnaya people were few in number, rare infrequency, and when they did happen, involved primarilyMaikop women, not men. If more mating had occurred, wewould see more EHG among the Maikop genomes and moreAnatolian Farmer among Yamnaya steppe genomes than we dosee. Of course another, final, possibility, consistent with thearchaeological and genetic evidence presented here, is thatthere were two phases of interference from Caucasianlanguages in two periods. The first, perhaps responsible forsome of the basic morphological and phonological traitsBomhard detected, could have occurred in the fifth millenniumBC and involved very archaic eastern Caucasian languages thathad moved to the lower Volga steppes with CHG people, wherethey intermarried with Samara-based EHG pre-Uralic people tocreate early PIE and the Khvalynsk culture and a newEHG/CHG genetic admixture; and the second phase, which left a Northwest Caucasian imprint over late PIE, perhaps moresuperficial (lexical) than the earlier interference, could havebeen during the Maikop period, but without a major geneticexchange between Maikop and Yamnaya."

I would opt for the latter.