Origin of horse domestication likely on the North Caspian steppes

Open access Late Quaternary horses in Eurasia in the face of climate and vegetation change, by Leonardi et al. Science Advances (2008) 4(7):eaar5589.

Interesting excerpts (emphasis mine):

Here, we compiled an extensive continental-scale database, consisting of 3070 radiocarbon dates associated to horse paleontological and archeological finds across the whole of Eurasia, that has been analyzed in association with coarse-scale paleoclimatic reconstructions. We further collected the number of identified specimens (NISP) frequency data for horses versus other ungulates in 1120 archeological layers in Europe (…) This ma.ssive amount of data allowed us to track,with unprecedented details, how the geographic distribution of the species changed through time

Geographic range through time

For most analyses, the data have been divided into climatic periods: pre-LGM(older than 27 ka B.P.), LGM(27 to 18 ka B.P.), Late Glacial (18 to 11.7 ka B.P.), Preboreal (11.7 to 10.6 ka B.P.), Boreal (10.6 to 9.1 ka B.P.), Early Atlantic (9.1 to 7.5 ka B.P.), Late Atlantic (7.5 to 5.5 ka B.P.), and Recent (younger than 5.5 ka B.P.) (Fig. 1, A and B). The spatial and temporal distribution of horse remains compiled in our database reveals a strong imbalance in Eurasia (Fig. 1, A and B).

We found a common trend in both regions for a high number of occurrences at the end of the Pleistocene (with a decrease during the LGM, only visible in Europe), followed by a drastic reduction in the Early and Middle Holocene, and a relative increase toward more recent times. These included both the Early Atlantic in Europe, which started ~9.1 ka B.P., and the time range after 5.5 ka B.P. for Asia. The horse fossil record appears ubiquitous throughout Europe in the Late Pleistocene, while in the Early and Middle Holocene the finds are concentrated in central-western Europe and Iberia. From 7.5 ka B.P., the number of finds increases markedly, and the geographical distribution extends toward the east and southeast.

Horse occurrences through time. (A) Horse occurrences through time. Histograms showing the number of horse observations in Europe (left panel) and Asia (right panel) for each time bin (top) and for climatic period (bottom). Only time bins with more than 10 observations (black horizontal line) have been considered for the SDM analyses. From 22 ka B.P. backward (gray vertical line), time bins cover 2 ka following the available paleoclimatic reconstructions. The central map shows the boundaries considered while defining European and Asian regions, with the black line representing the Urals. The zoomed area shows the geographical resolution of the climatic reconstructions, with each pixel representing a grid cell. (B) Geographic distribution of horse occurrences. Maps showing horse occurrences for each climatic period in Europe (left) and Asia (right).

Different Asian and European niches

This analysis revealed that, in both continents, horses occupied only a portion of the climatic space available. The range covered by random locations shows that the paleoecological conditions present in Europe were only a subset of those found in Asia. However, European horses occupied a much wider climatic space than in Asia, with only limited overlap between the two ranges.

Horses conquered temperate environments from a European source

There is no evidence of climatic barriers between those two populations through time because the forecasts from Europe and Asia always overlap in central Eurasia, except 5 ka B.P. (figs. S3 and S4). An alternative explanation is the role of the Urals as a potential constraint for the dispersal of horses between Europe and north central Asia.

Climatic suitability. (A) Cumulative climatic suitability for the past 44 ka based on simulation on the European (left), Eurasian (middle), and Asian (right) data sets. To correct for sampling bias in the Eurasian data set, for each time slice, all estimates and projections for Eurasia are performed considering 100 random resampling of European occurrences in the same number as Asian occurrences. The darker the colors, themore stable the climatic suitability for horses (climatic niche = p-Hor) through time. (B) Projection of climatic suitability across Eurasia in different climatic periods based on occurrences in Europe (left), Eurasia (middle), and Asia (right). Because of the scarcity of data available for Asia, no models for the Holocene have been possible for both Asia and Eurasia, with the exception of 5 and 3 ka B.P. (both included in the “Recent” period).

Climatic and habitat association patterns for horses in Europe support increasing habitat fragmentation

The decrease of horse remains in Europe is not characterized by a geographic reduction in the overall extent of the area occupied by the species but in a drop of frequencies in a geographic extent that does not vary much between the Late Glacial and the Early Atlantic (Figs. 1B and 4B). This pattern is more likely to result from habitat fragmentation than from a geographic shift in the climatic range suitable for the species, as observed for many animals during the LGM (23).

In the whole period ranging from the Preboreal (11.7 to 10.6 ka B.P.) to the Late Atlantic (7.5 to 5.5 ka B.P.), the total amount of land space most and likely suitable to horses is wider than in the Late Glacial, and only between 8 to 7 ka ago the European range appears patchy and fragmented (Fig. 4C). When comparing each of four successive time bins during the Holocene (8, 7, 6, and 5 ka B.P., respectively) (Fig. 4E), the difference in successive p-Hor values in Europe shows that the suitability for the species in Iberia, northeastern France, Italy, the Balkans, and eastern Europe steadily increased, while in Central Europe strong differences can be observed between neighboring regions.

Analyses of the European data set and biomefrequency. (A) Distribution through time of the frequency of horse remains in Europe calculated as NISP of horses versus other ungulates. (B) Density of horse remains through time in Europe, calculated as NISP of horses versus other ungulates. The numbers at the bottom of each bar represent the number of observations falling in each class, from 0 to >5%. (C) Climatic suitability for horses in Europe between 10 and 3 ka B.P. (D) Climatic suitability per time period. Percentage of land cells in Europe with a value of suitability for horses (p-Hor) > 0.5 and p-Hor > 0.8. (E) Holocene climatic amelioration. Difference in p-Hor in Europe comparing five successive time bins during the Holocene: 9, 8, 7, 6, and 5 ka B.P. Eachmap shows the difference in themore recent distribution compared to the previous one. (F) Environmental reconstructions in themacro area surrounding horse finds in Europe (left) and Asia (right) per climatic period. The lighter the color, the less forested is the region. The numbers at the bottom of the bars show the number of occurrences in closed environments over all the observations. The dotted line represents a frequency of 0.5.

Taken at face value, this pattern would suggest that horses were not restricted to open environments but could equally well inhabit closed, forested environments, as previously suggested (18). However, as others recently emphasized (19), the faunal associations inHolocene sites from Europe suggest a different pattern. The PCAs based on faunal assemblages (figs. S1 and S2) separate on the second principal component sites characterized by ungulates associated to forested areas (red deer, wild boar, and roe deer) and all other animals, associated to semi-open and open environments, including horses for most records.

Together, the contrast between the reconstructed microscale and macroscale vegetable coverage in Europe, the increase of horses in mainly forested macroregions, and the spatial pattern of extinction suggest that, from the beginning of the Holocene, the suitable environment became more and more patchy, with open areas increasingly fragmented by forests, where wild populations of horses could have survived in isolation until one or several waves of arrivals of domestic horses, leading to either local admixture or a full replacement of the preexisting local populations.


Our data show that, up to 5.5 ka ago, horse finds do not show association with species characteristic of forested areas such as wild boar and roe deer. We infer that the open and semi-open habitats occupied by horses on a narrow geographic scale appear less and less frequent at a macroenvironmental scale, supporting the possibility of increasing fragmentation of open habitats. This event is also likely to have led to an intensification of genetic isolation for the remaining horse populations, a pattern that still needs to be tested on genomic data.

The suitability of both Iberia and eastern Europe appears constant throughout the entire post-LGM period, in line with these regions being hotspots of genetic diversity and, possibly, the refugia sources for the recolonization of the continent (11). While the Pontic-Caspian region appears not suitable for European horses around the time when horses where first domesticated some 5.5 ka ago (6), part of this region appears suitable for the Asian horses (with the Caspian Sea as the westernmost boundary). This may suggest that horse domestication started from a population background related to an Asian ancestry and that the further spread of the domesticated horses in Europe involved either adaptation to novel niches (possibly through selective breeding) or the application of domestication techniques to local horse populations pre-adapted to these environmental conditions. Testing this scenario will require mapping the genetic structure of the Eurasian horse population within the fifth to third millennium BCE.

Some remarks

Cultural-anthropological research and archaeological remains (see here), genetics (see here and here), and now also thorough palaeoclimatic and archaeological models point to the North Caspian region, settled by the Khvalynsk culture, as the most likely earliest origin of horse domestication. The paper also supports the favorable conditions of western Europe up to Iberia for the introduction of a horse-riding culture.

I intended to write a post about the myth of Corded Ware horse riders, but for the moment I haven’t found the time. Not that Corded Ware pastoralists didn’t have horses, or could not ride them: they were a highly mobile culture of pastoralists stemming from eastern Poland / western Ukraine, so they must have known horses, like many other European cultures of the late 4th / early 3rd millennium influenced by expanding Yamna settlers. But it just cannot be said to have formed an essential part of their culture, as it was for Khvalynsk-Novodanilovka, and especially Yamna and later East Bell Beaker, Sintashta, etc.

A mere look at these maps suffices to assess the limited role of the horse in north-eastern Europe, the only region where groups of late Corded Ware-derived cultures survived the expansion of Yamna, and especially East Bell Beakers after ca. 2500 BC, which transformed Western, Northern, and Central Europe, and even East Europe reaching the modern Baltic countries, Belarus, and Romania. Even Trzciniec was born out of the influence from expanding Bell Beakers into earlier Corded Ware territory, although the later (Iron Age) relevance of this culture was probably quite limited.

As you can imagine, without horses and horse symbolism, horse riding, carts, and intensive cattle-breeding (associated with Yamna and the broad, east-central European grasslands typical of steppe regions), there can be no Proto-Indo-European, whose reconstructed vocabulary is particulary rich in horse-related words, and whose reconstructed culture, society, and religion cannot be understood without the domesticated horse. In forest regions to the north-east and eastern Europe, there was apparently little space for horses, but plenty of room for other ungulates and thus hunting, and indeed Uralic languages

In the upcoming months we will see R1a-fans associating Proto-Indo-Europeans more and more with wool, and sheep, and corded ware, and forest regions, until the proposed homeland shifts to the Baltic and Finland, instead of dat boring horse-riding people of the steppes…No wait, it’s already happening.

NOTE. Also open access is the recent Horse Y chromosome assembly displays unique evolutionary features and putative stallion fertility genes, by Janečka et al. Nature Communications (2018).


Climatic conditions in the Cis-Ural Steppe region and the Repin culture


New paper (behind paywall) Climate and Vegetation Changes over the Past 7000 Years in the Cis-Ural Steppe, by Khokhlova, Morgunova, Khokhlov, and Gol’eva, Eurasian Soil Sc. (2018) 51: 506.

Abstract (emphasis mine):

A multilayered archaeological site Turganik Settlement in the valley of the Tok River in the Cis- Ural steppe (Orenburg oblast) was examined with the use of paleopedological and microbiomorph methods. Ancient people inhabited this area in the Latest Neolithic (Eneolithic) (5th millennium BC) and Early Bronze (4th millennium BC) ages. It was found that cultural layers dating back to the Atlantic period of the Holocene had been formed under conditions of a predominance of grassy–forb vegetation with a small portion of tree species and dry climate; the ancient settlement was not affected by floods and was suitable for permanent living. It is probable that soils of the chestnut type with salinization and solonetzic features were developed in that time. The final stages of the accumulation of cultural layers were marked by strong shortterm floods, whose sediments partly masked the features of the previous long arid epoch. The highest degree of aridity was at the end of the Atlantic period. In the Subboreal and Subatlantic periods, soils of the meadowchernozemic type were formed; the spore–pollen spectra of these periods are characterized by a higher portion of tree species and by the presence of phytoliths of meadow grasses. The climatic conditions were generally colder and more humid, though some short-term aridization stages could take place. Some of these stages are recorded in the thickness of the studied sediments.

Interesting excerpts:

Paleosols buried under archaeological monuments of different periods represent a valuable archieve of information about the paleoenvironment. Most of the works in the field of archaeological pedology deal with earthen burial sites and kurgans [2, 5, 7, 9, 11]. Paleosols buried under the kurgans present us the paleoenvironmental records of a relatively short time before they were buried under the kurgan bodies. The study of kurgans created in different times makes it possible to characterize paleosol sequences storing information on longer periods of time in the second half of the Holocene. However, groups of kurgans that were consecutively created during the entire time span of kurgan construction, beginning from about 6000 yrs BC to the Early Medieval epoch, are few in number [8, 18, 22]. Even for such groups of kurgans, there are considerable time intervals that cannot be characterized because kurgans were not constructed during them. Hence, it is impossible to study the soils buried during these intervals. To reconstruct paleoenvironmental conditions for them, certain interpolation is required [29].

At the same time, there are archaeological sites — ancient settlements — the material of which gradually accumulated during very long time, e.g., beginning from the Middle Holocene to the present. Though such objects may also contain “missing layers” for certain periods, when the processes of denudation, erosion, or deflation predominated over sediment accumulation, they represent an almost continuous record on information about the paleoenvironmental conditions from the beginning of their functioning [25]. The most valuable among such sites are those that retain information on those periods of the Holocene that cannot be characterized on the basis of available data on the paleosols buried under the kurgans. In particular, this is the Atlantic period (7500–5000 yrs ago), because the construction of kurgans began only in the second half of this period (within the Volga–Ural interfluve [14]), and such ancient kurgans are rarely found. We studied such an archaeological site in the valley of the Tok River in the Cis-Ural steppe zone in Orenburg oblast. This site is known as the ancient Turganik settlement.

We studied different layers of the Turganik settlement with the use of a set of methods in order reconstruct the paleoenvironmental conditions (climate and vegetation) for the entire period of the accumulation of these sediments.

Thus, the Atlantic period of the Holocene in the Cis-Uralian steppe was characterized by dry climatic conditions with the driest stage during the Early Bronze Age (the Early Yamnaya culture of the middle of the fourth millennium BC). The Subboreal and Subatlantic periods were generally colder and wetter, though they also included short-term aridization phases, some of which were recorded in the sediment thickness.

This site is at the core of the interaction of Samara, Khvalynsk, and Repin cultures during the Eneolithic.

You can read more about it and the nature of Repin described by Morgunova (in favour of Gimbutas’ model), as combining traditions from Eneolithic steppe cultures from Khvalynsk to Sredni Stog, e.g. in Pottery from the Volga area in the Samara and South Urals region from Eneolithic to Early Bronze Age (2015).

Eneolithic settlements (1–5, 7, 10–16, 20, 22–43, 48, 50), burial grounds (6, 8–9, 17–19, 21, 47, 49) and kurgans (44–46) of the steppe Ural-Volga region: 1 Ivanovka; 2 Turganik; 3 Kuzminki; 4 Mullino; 5 Davlekanovo; 6 Sjezheye (burial ground); 7 Vilovatoe; 8 Ivanovka; 9 Krivoluchye; 10–13 LebjazhinkaI-III-IV-V; 14 Gundorovka; 15–16 Bol. Rakovka I-II; 17–18 Khvalunsk I-II; 19 Lipoviy Ovrag; 20 Alekseevka; 21 Khlopkovskiy; 22 Kuznetsovo I; 23 Ozinki II; 24 Altata; 25 Monakhov I; 26 Oroshaemoe; 27 Rezvoe; 28 Varpholomeevka; 29 Vetelki; 30 Pshenichnoe; 31 Kumuska; 32 Inyasovo; 33 Shapkino VI; 34 Russkoe Truevo I; 35 Tsaritsa I-II; 36 Kamenka I; 37 Kurpezhe-Molla; 38 Istay; 39 Isekiy; 40 Koshalak; 41 Kara-Khuduk; 42 Kair-Shak VI; 43 Kombakte; 44 Berezhnovka I-II; 45 Rovnoe; 46 Politotdelskoe; 47 burial near s. Pushkino; 48 Elshanka; 49 Novoorsk; 50 Khutor Repin.

The migration model of Anthony (2007, 2015), who collaborated with this group, is a more precise description of how peoples from the east of the Don River (mainly Khvalynsk/Repin cultures) migrated to develop a greater Yamna community, with Repin-type material culture expanding east of the Urals (into Afanasevo) and west of the Don River (into previous Sredni Stog/Kvitjana territory) – which I followed for the Indo-European demic diffusion model (we have recent samples of other potential Khvalynsk/Repin-related migrations).

NOTE. I usually refer to this Khvalynsk/Repin migration in genomics as of ‘Khvalynsk migrants’, for simplicity purposes, given that the few samples we have are from Khvalynsk, and that cultural regions east of the Don are difficult to differentiate precisely. However, it remains to be seen if – as I proposed – there are genetic differences between Repin and Khvalynsk groups, especially regarding R1b-L23 subclades – I proposed mainly Z2103 for Khvalynsk, L51 for Repin, a difference which has not been confirmed for the moment in Afanasevo, probably of Pre-Tocharian dialect, an archaic Northern dialect of Late PIE.

Anthony’s model of Khvalynsk/Repin as Yamna forefathers is probably, as we are seeing in Yamna samples, the right interpretation of peoples behind pots, compared to Gimbutas’ general idea of expanding kurgans of the 1970s.

On the other hand, the alternative Russian school version of Yamna developing from a heterogeneous community of Khvalynsk-Sredni Stog-Lower Danube cultures is probably by now to be fully dismissed, in archaeology (as Morgunova says) as in genetics.


Indo-Europeans and Finno-Ugric peoples might have shared the love for weed


Funny and interesting read to help relax the trolling wave caused by the first early Hittite samples:

Cannabis is indigenous to Europe and cultivation began during the Copper or Bronze age: a probabilistic synthesis of fossil pollen studies, by McPartland, Guy, & Hegman, Vegetation History and Archaeobotany (2018).

Abstract (emphasis mine):

Conventional wisdom states Cannabis sativa originated in Asia and its dispersal to Europe depended upon human transport. Various Neolithic or Bronze age groups have been named as pioneer cultivators. These theses were tested by examining fossil pollen studies (FPSs), obtained from the European Pollen Database. Many FPSs report Cannabis or Humulus (C/H) with collective names (e.g. Cannabis/Humulus or Cannabaceae). To dissect these aggregate data, we used ecological proxies to differentiate C/H pollen, as follows: unknown C/H pollen that appeared in a pollen assemblage suggestive of steppe (Poaceae, Artemisia, Chenopodiaceae) we interpreted as wild-type Cannabis. C/H pollen in a mesophytic forest assemblage (Alnus, Salix, Populus) we interpreted as Humulus. C/H pollen curves that upsurged and appeared de novo alongside crop pollen grains we interpreted as cultivated hemp. FPSs were mapped and compared to the territories of archaeological cultures. We analysed 479 FPSs from the Holocene/Late Glacial, plus 36 FPSs from older strata. The results showed C/H pollen consistent with wild-type C. sativa in steppe and dry tundra landscapes throughout Europe during the early Holocene, Late Glacial, and previous glaciations. During the warm and wet Holocene Climactic Optimum, forests replaced steppe, and Humulus dominated. Cannabis retreated to steppe refugia. C/H pollen consistent with cultivated hemp first appeared in the Pontic-Caspian steppe refugium. GIS mapping linked cultivation with the Copper age Varna/Gumelniţa culture, and the Bronze age Yamnaya and Terramara cultures. An Iron age steppe culture, the Scythians, likely introduced hemp cultivation to Celtic and Proto-Slavic cultures.

Interesting excerpts (modified to make them more readable):

C. sativa during the Copper age

We compared the territories of Copper age cultures with locations of C–H pollen consistent with Cannabis in Fig. 5. This suggests that two Copper age cultures had the potential to domesticate wild-type C. sativa: the Greek Chalcolithic, and the Cucuteni-Tripolye culture. C–H pollen consistent with cultivated Cannabis occurred at one site in Bulgaria. This site may correspond to the Varna culture or Gumelniţa culture. However, pollen at five other Varna and Gumelniţa sites was interpreted as Humulus, or undetermined C/H. Archaeological studies of Gumelniţa and Cucuteni-Tripolye sites have found C. sativa seeds and less-robust evidence—pottery seed impressions (Clarke and Merlin 2013; Long et al. 2017; McPartland and Hegman 2017).

Cannabis distribution ca. 4,500–2,300 cal BP.

C. sativa during the Bronze age

Eight Bronze age cultures had potential: C–H pollen consistent with wild-type Cannabis in Fig. 6 appeared within the boundaries of several Bronze age cultures. These include the Netted Ware culture, Ezero culture, Yamnaya culture, Corded Ware culture, Bell-Beaker culture, Terramara culture, Aegean Bronze age, and Mycenaean Greece. C–H pollen interpreted as cultivated C. sativa appeared in four studies: One study in Yamnaya territory agrees with archaeological studies, which have recovered C. sativa seeds or pottery seed impressions (Clarke and Merlin 2013; Long et al. 2017; McPartland and Hegman 2017). Two study sites are associated with the Terramara culture. However, pollen in 11 other studies at Terramara sites suggested Humulus or indeterminate C/H pollen. One FPS in France was likely contaminated by taphonomic processes, as admitted by its authors.

Scythian contacts with Celts and Balto-Slavs

The Scythians impacted deeply on the Celts, in the realms of art, animal husbandry, military strategy, language, and even clothing. The oldest evidence of Scythian–Celtic interactions that we could find was a 7th century bce burial in Bulgaria, which combined elements of Scythian culture along with a Hallstatt vessel (Braund 2015). Scythian artifacts in Hallstatt-occupied Hungary first appear around 550 bce (Bartosiewicz and Gál 2010). A Hallstatt burial at Vix in France from 525 bce contains items and motifs inspired by Scythian culture (Megaw 1966). These data collectively suggest a conservative date of 550 bce as the terminus post quem for Scythian contact with the Celts. Only three sites in Celtic territory showed pollen signals consistent with hemp cultivation prior to 550 bce. To wit, the oldest ones had problems with dating. In contrast, 28 FPSs in Celtic territory showed pollen signals of hemp cultivation arising post-550 bce, after their contact with the Scythians.

The Scythians also impacted Proto-Slavic cultures. The Scythians left a trail of burned-out settlements built by the Proto-Slavic Lusatian culture around 600 bce (Bukowski 1977). A horde of Scythian artifacts found at Witaszkowo in Lusatia dates to 550 bce (Furtwängler 1883). Only two pre-550 bce sites in Slavic/Baltic territory showed signals consistent with hemp cultivation, and they occurred in the southeast, towards the Scythian homeland. Ralska-Jasiewiczowa and van Geel (1998) linked the appearance of Cannabis pollen in Poland with Scythian incursions. The Scythians appear to be responsible for the spread of Cannabis amongst several Iron age European cultures.

There you have it, the long-sought Yamna – Corded Ware cultural connection. Finno-Ugric peoples liked it wild, though 😉

On the potential origin of Caucasus hunter-gatherer ancestry in Eneolithic steppe cultures

An interesting open genomic question is the origin and spread of Caucasus hunter-gatherer (CHG) ancestry in steppe populations during the Eneolithic.

My broad theory regarding the appearance of this ancestral component is based on:

Two recently published papers ivestigating the Don Region may shed some light on this issue:

Plant food subsistence in the human diet of the Bronze Age Caspian and Low Don steppe pastoralists: archaeobotanical, isotope and 14C data, by Shishlina, Bobrov, Simakova, et al. Veget Hist Archaeobot (2018).

EDIT (16/3/2018): You can now read or download the paper at Academia.edu.


The paper presents the result of analysis of charred food on the interior part of the vessels from the graves of the East Manych and West Manych Catacomb archaeological cultures (2500–2350 cal bc). The phytolith and pollen analyses identified pollen of wild steppe plants and phytoliths of domesticated gramineous plants determined as barley phytoliths. Direct 14С dating of one of the samples demonstrates that barley spikelets and stems were used in funeral rites by local steppe communities. However, there are no data suggesting that steppe inhabitants of the Lower Don Region were engaged in agriculture in the mid-3000 bc. Supposedly, barley could have reached the steppes through seasonal migrations of mobile pastoralists to the south, use of North Caucasus grasslands in the economic system of seasonal moves and exchange with local people. Nevertheless, presence of carbonized barley seeds in the occupation layers at North Caucasus settlements of 4000–3000 bc requires confirmation by direct 14С dating of such samples.

Location of sites. 1: Ulan IV; 2: Peschany IV and V; 3: Shakhaevskaya 1; 4: Zunda-Tolga 2; 5: Lesnoye; 6: Chidgom; 7: Meshoko; 8: Chishkho; 9: Svobodnoye

Dynamics of Chemical and Microbiological Soil Properties in the Desert–Steppe Zone of the Southeast Russian Plain during the Second Part of the Holocene (4000 BC–XIII century AC), Kashirskaya, Khomutova, Kuznetsova, et al. Arid Ecosyst (2018) 8(1):38-46.


The results of studies of the chemical and microbiological properties of the soils buried under the barrows of the Eneolithic, Bronze, and Middle Ages periods of the southeast of the Russian Plain are presented. It was shown that the climate of the region in the Eneolithic period (4200–4100 BC) and in the Middle Ages (700 years ago) was more humid in comparison to the present time. The third millennium BC was characterized by a gradual increase of the climate aridity. Its peak was at the end of the III millennium BC. The number and biomass of microbial cells was maximal in soils buried in periods of high atmospheric humidity (4200–4100 and 3000–2800 BC) and sharply decreased during the aridization period in the second half of the III millennium BC. In general, the variability of indicators of microbocenosis conditions of desert–steppe buried soils of all ages from the burial mounds correlated with the centuries-old dynamics of the climate.

Number of microbial cells in buried soils of different ages and modern background soil.

It is well known that access to more food – as in favorable crops and cattle feeding – may cause demographic explosions, and the second article – together with recent genomic data – may be yet another proof of that.

Until now, pastoralism seemed to be the main subsistence economy for most steppe groups. It seems that earlier Eneolithic contacts of certain steppe groups with settlements of the Northern Caucasus might have been not just to obtain prestige goods though, but – if proper radiocarbon dating confirms it – also implied essential goods, and maybe more stable seasonal exchange systems.

Such stable economic exchanges might have therefore included bidirectional exogamy practices, justifying the sizeable genomic contribution from the Caucasus.

At this point this is just another good theory to take into account.