The definition of Sredni Stog phenomenon (SSP) varies and is often a loosely applied term to refer to pretty much any individual in the Dnieper and Don regions between the ‘Neolithic’ and Yamnaya periods. In order to elucidate the SSP, some brief remarks on the preceding Mariupol phenomenon are warranted. Understanding the Mariupol horizon is fairly straightforward – its development was catalysed by an intrusion of groups from somewhere west of the Dnieper, ~ 5500BC. The ‘proto-Mariupol’ group were genomic and economic ‘hunter-gatherers’, lacking any discernible EEF admixture, and with Y-hg I-L702 uniparental ‘trace-dye’. The Mariupol phenomenon predominantly impacted the lower reaches of the Dnieper and Azov steppe (Lower Dnieper- Azov group, ‘LDA’), but extended toward the Don, Volga and even the Kuban steppe in an attenuated form. The elevated levels of “Ukr N’ in Golubaya Krinitsa and the Y-hg I2a-L702 individual at Berezhnovka attest to this movement. The Mariupol phenomenon is associated with the development of formal cemeteries, linking them with Late Neolithic mixed farmer/HG groups in the northeast Balkans. Individuals were buried in a ‘supine straight-legged’ inhumation, with grave goods such as boar-tusk pendants for select males and adorning shell beads for females. This might signal the emergence of gender-differentiation in burials and the rise of local leaders or ‘chiefs’. Data sets treat the ‘Neolithic’ in Ukraine as a monolithic phenomenon, however it is important to note that Dereivka stands apart – it is 200km north of other “Ukraine_N” sites such as Volnienski, Igren and Vovnigi, beyond the ‘Dnipro bend’. Moreover, male individuals from Dereivka are overwhelmingly assigned to Y-hg R1b-V88 and the burial pose (N-S) at Dereivka deviates from the more common E-W orientation seen elsewhere. Quite a few of the published ‘Sredni Stog’ individuals are from Dereivka, and often earlier than 4500BC, and N. Kotova assigns them to the Dnieper-Donets culture. Moreover, the recently published middle Don individuals, such as those from Golubaya Krinitsa and Vasilyevsky Cordon -17, are also not Sredni Stog, but can be thought of as ‘partially Mariupolised hunter-gatherers’. In another example, the (undated) ‘Sredni Stog’ individual I27930 from Igren was assigned to Y-hg Q and he can be modelled as a 2-way mix of EHG & WHG. This individual is actually from the Mesolithic. So what occurred during the Sredni Stog period? In contrast to the Mariupol phase, the population dynamics associated with SSP are complex: at least three external flows can be highlighted (i) the advance of Tripolje communities from the Carpathians to the Dnieper (ii) arrival of South-Caucasian/CHG agro-pastoralists in the north Caucasus, and (iii) arrival of ‘central Asian’ populations in Volga-Caspian region (represented by “TTK individual’); in addition to intra-steppe shifts and flows. Notwithstanding, the ‘ideological background’ of SSP is rooted in the Mariupol horizon. The stereotypical SSP burials features individuals buried on their back, but increasingly with legs up-flexed. And we see the beginnings of kurgan constructions, which vary from stone cairns to soil-thrown barrows. Most are buried in simple pits, however some have more complex ‘catacomb’ pits. What happened in the Dniester-Dnieper-Don region during the SSP? We can begin by orientating ourselves with a PCA to observe two main clines developing. One cline develops between ‘Ukr_N and EEF and a second cline pulls toward Lower-Volga Caucasus groups. The first cline mostly comprises of ‘Farmers’ from Tipolje and ‘hunter-gatherers’ from Dereivka. The second cline consists of individuals from Dereivka and the lower Dnieper-Azov group pulling toward Lower Volga-Caucasus groups.Admixture analysis with qpAdm reveals 3 groups within the 2 broad clines. The first group can be thought of as ‘core Sredni Stog’. These individuals are 2-way mixes of ‘Ukr_N’ and ‘Steppe Eneolithic’ (sometimes Progress works, sometimes Remontoye or Berezhnovka). They are both males and females. In our examples, the females are from Kopachiv Yar (4000 BC) and Dereivka (3500BC). The males come from Dereivka (4300BC), Moluykhiv Bugor (4000BC), Vynohrado (4000BC); they are all derived for Y-hg I2a-L703+. These results represent a blending of social networks between the LDA and various lower Volga-Caucasus groups, and the subsequent expansion by LDA further West. The terminus ante quem of 4300 BC matches the corrected dating of the Kuban steppe sites such as Progress & Vojnuchka.Another subset comprises of individuals from Dereivka and Verteba cave who situated on an ‘Ukr-N’ < - - > EEF cline. Many of the earlier Dereivka individuals are almost 100% Ukr_N. Verteba cave Tripolje can be modelled as 80% EEF + 20% Ukr_N. One individual from Dereikva (I3719) falls outside the Dereivka <-> Tripolje clin, as he plots further ‘south’ with Balkan-LBK farmers. Consistently, he comes out as ~100% EEF with qpAdm. Dating to ~4700BC, he precedes the arrival of Tipolje groups to the region by hundreds of years. FtDNA have assigned him to I2-Z161- FTH81, which is distinctive to the LDA haplotypes and is phylogenetically linked to a Czech LBK individual.A third group consists of individuals with more complex 3-way ancestries, consisting of EEF, Ukr-N and Steppe_En and/or Maikop. These come from late Dereivka and late Tripolje groups, in archaeological literature often termed as ‘Soldanesti’, ‘Zhivotilovksa-Volchansk’, Cernavoda (Kartal). Once again, the males from Soldanesti and Cernavoda derive from LDA-related Y-hg I2a-L703 in some shape or form.Conclusions: 1) Firstly, we note that the Dereivka group was subject to early EEF influence, as soon as eastern LBK groups reached Ukraine after 5000BC. However, their main interaction occurred with the younger, Tripolje group, which expanded toward the Dnieper after ~ 4300 BC. 2) In the LDA group we observe patrilineal continuity. These clans created expansive social-networks. They initially mixed with groups from the lower Volga-Caucasus area. Some then moved west, and ‘took over’ the Tripolje region and acquired high levels of EEF. 3) As a third conclusion, we can reject the commonly held notion that Tripolje was ‘conquered by Yamnaya pastoralists’. Our analysis instead highlights that their core structure fragmented as they became intertwined with powerful networks to their west (Trpolje) and east (Sredni Stog). The ‘take-over’ was due to the expansion of LDA/ SS groups. Mixed groups emerged such as Cernavoda and Soldanesti, which retained Tripolje ancestry and some cultural traditions. By the time Yamnaya groups reached the Dniester forest steppe, Tripolje had been long gone.
