Are Bactrian (BMAC) horses not horses?

Librado, P., Khan, N., Fages, A. et al. The origins and spread of domestic horses from the Western Eurasian steppes. Nature 598, 634–640 (2021). https://doi.org/10.1038/s41586-021-04018-9

This paper was published in October 2021. The following is the abstract:

Domestication of horses fundamentally transformed long-range mobility and warfare. However, modern domesticated breeds do not descend from the earliest domestic horse lineage associated with archaeological evidence of bridling, milking and corralling at Botai, Central Asia around 3500 BC. Other longstanding candidate regions for horse domestication, such as Iberia and Anatolia, have also recently been challenged. Thus, the genetic, geographic and temporal origins of modern domestic horses have remained unknown. Here we pinpoint the Western Eurasian steppes, especially the lower Volga-Don region, as the homeland of modern domestic horses. Furthermore, we map the population changes accompanying domestication from 273 ancient horse genomes. This reveals that modern domestic horses ultimately replaced almost all other local populations as they expanded rapidly across Eurasia from about 2000 BC, synchronously with equestrian material culture, including Sintashta spoke-wheeled chariots. We find that equestrianism involved strong selection for critical locomotor and behavioural adaptations at the GSDMC and ZFPM1 genes. Our results reject the commonly held association between horseback riding and the massive expansion of Yamnaya steppe pastoralists into Europe around 3000 BC driving the spread of Indo-European languages. This contrasts with the scenario in Asia where Indo-Iranian languages, chariots and horses spread together, following the early second millennium BC Sintashta culture

I have a serious problem with the emphasized part, and the emphasis is mine. So I exchanged mails with the authors. They are pasted below. Thoughts in the comments will be appreciated.

To: ludovic.orlando@xxxxxxxxxx
Hello,
Congratulations on your published paper. I am an amateur genomics blogger and had a few queries, specifically regarding this sentence from the paper.

"This contrasts with the scenario in Asia where Indo-Iranian languages, chariots and horses spread together, following the early second millennium BC Sintashta culture11,12."

I will list my queries pointwise:

1. A Problem of the Earliest Horse Domestication. Data from the Neolithic Camp Ayakagytma ‘The Site’, Uzbekistan, Central Asia
This 2009 paper claims finding evidence of domesticated horses between 6000-5400bce in Uzbekistan. I believe none of the samples have been analyzed in your paper.

2. The Katelai site in Swat, Pakistan has 2 horse burials (Narasimhan et al 2019, Supplement pg 154). These have not been analyzed either.

3. And finally, we have horses from BMAC
THE INDO.IRANIAN PROBLEM IN THE LIGHT OF THE LATEST EXCAVATIONS IN MARGIANA- V. Sarianidi 
 The domesticated horse was known to the BMAC tribes as early as on the eve of the second millennium BC. This was proved by the excavations in Bactria where bronze sceptre tops were found in the form of horse heads with carefully plaited mane (Sarianidi 1982, fig. 2). Also their cylinder seals bear horse images (Sarianidi 1998b, nos. 1441, 1442,1444, etc.)  

 And, finally, one should mention the burial of an about one-year-old foal that was found at the Gonur necropolis. The foal was headless and its skeleton was placed in the correct anatomical order

The image of a spoke-wheeled chariot on a cylinder seal from the grave of the Hissar IIIB of the BMAC (Schmidt 1937, ftg. 118) proved the fact that chariots were not foreign to the people of the BMAC.  
These horses from gonur are dated to 2200-2100 bce (V Narsimhan et al 2019). The chariot seal from Tepe HissarIIIB is dated to 2000 bce (A Parpola 2020). This is before there was any genetic impact of Sintashta on BMAC (V Narasimhan et al, 2019). The Gonur horses have also not been tested.
My question is:
Given the above data from the region which would be the indo iranian speaking lands, and given that none of the horse remains have been analyzed, and given that the horse and chariot seal are dated to a period before any genetic impact of sintashta on the region - how can you make the claim that "horses and chariots spread together with indo iranian languages following the sintashta culture"?
Awaiting your response,
Thanks

The reply I got is pasted below

To: ME
Cc: Alan Outram (A.K.Outram@xxxxxxx)
Dear xxxxx
Thanks for reaching out to me and for your interest in our study. You certainly raise important points. I have taken the time to rapidly discuss those points with Prof Outram, one of our leading archaeologists in this study, before replying to you. Our answers are just below.
I hope that this will answer your questions.

Best

1. Our paper does not rule out earlier attempts at horse husbandry, though the cases you outline present limited evidence compared to other cases. Species abundance or burial alone are insufficient.

2. The Narasimhan article indicates that graves at the Katelai site could date back to 1000-800 BCE (only a handful are radiocarbon dated though), which appears to post-date by quite a margin the horse expansion uncovered in our work. While we cannot be sure about the genetic profile of these horses as they could not be sampled and, thus, sequenced, we could expect them to show the genetic profile found in all other horses analyzed across all the other regions. At the time the horse population structure was almost homogeneous across Eurasia and, thus, it cannot provide insights onto migration patterns. You raise however a very fair point: even though our work includes the largest ever collection of ancient genomes from an animal species, our sampling efforts should be increased in many regions, including those you indicate, as well as others such as Greece and Macedonia as they remain poorly documented at the genetic level.
 
3. There is indeed need for further research to understand the exact nature of the rapid spread of DOM2 and other equestrian materials such as chariots. We make this note of caution in our paper: "We, however, acknowledge substantial spatiotemporal variability and evidential bias towards elite activities, so we do not discount additional, harder to evidence, factors in equine dispersal." We clearly show that the traditional package or horses, language and genetics does not hold together in the spread to the West, but Eastwards they are still apparently synchronous. We are careful about the exact mechanisms involved. Indeed we end by inviting further  research "The results thus open up new research avenues into the historical developments of these different societal trajectories." It is likely that in some regions this was via human migrations, but in others through trade without significant patterning in human DNA patterns. Archaeologically we are challenged by the accuracy of dating. The spread appears very fast to some regions, but in fact dating methods do leave us with error margins representing multiple generations to past peoples. Thus what appears instant may have taken 100 years or more.
Prof Director Ludovic Orlando, PhD.

I was not convinced by their answer fully so this is my further mail to them to which no response has been received yet.

Dear Dr Orlando & Dr Outram,

Thank you for the response. Some of your comments are satisfactory, whereas some are still not. Let me outline those quickly.

1.	Our paper does not rule out earlier attempts at horse husbandry, though the cases you outline present limited evidence compared to other cases. Species abundance or burial alone are insufficient.

I agree that burial alone is insufficient evidence for domesticated horse. However, the horses in Gonur necropolis were purportedly found buried along with 4 wheeled wagons and other humans. 

1. Quotes from 2021, J.BENDEZU-SARMIENTO, Horse domestication history in Turkmenistan and other regions of Asia, MIRAS, 1, p. 17-29, emphasis mine. At Gonur-Depe, one finds the remains of at least six horses (one of them complete), and some ten proven asses [5; 6].The most important remains for science were no doubt the almost complete skeleton of a foal resting on a four-wheeled chariot (the wheels circled with bronze bands) which was found in royal grave №3200.2.

2. Quote from  The Oxus Civilization - C.C. Lamberg-Karlovsky, emphasis mine Tomb 3210 contained a silver “signal trumpet (…) for training of domestic horses”; one of five trumpets recovered (Sarianidi, 2009: 324, fig. 184) (Fig. 10c).  

3. Quote from Animal Burials and Cult of them in Margiana - NA Dubova. Some words need to be said about the discovery of horse remains. It becomes clear that we can only talk about one whole horse burial at Gonur: this was a young animal leaning against the east wall of the courtyard of the royal tomb 3200 and fixed against the side of a four wheeled cart. Only one tooth preserved from it which R Sataev identified as belonging to a horse (Sataev 2008a 2008b).It can be said with confidence that there was a domestic horse in Margiana.

The 4 wheeled vehicle was definitely a wagon/cart, but there indeed is some evidence that the Gonur animals were horses and that they were domesticated.

2. The Narasimhan article indicates that graves at the Katelai site could date back to 1000-800 BCE (only a handful are radiocarbon dated though), which appears to post-date by quite a margin the horse expansion uncovered in our work. While we cannot be sure about the genetic profile of these horses as they could not be sampled and, thus, sequenced, we could expect them to show the genetic profile found in all other horses analyzed across all the other regions. At the time the horse population structure was almost homogeneous across Eurasia and, thus, it cannot provide insights onto migration patterns. You raise however a very fair point: even though our work includes the largest ever collection of ancient genomes from an animal species, our sampling efforts should be increased in many regions, including those you indicate, as well as others such as Greece and Macedonia as they remain poorly documented at the genetic level.

Indeed the Katelai horses are likely to be the same genetic profile as the other horses of the same time period. It would have been great if these were analyzed as well to bolster your claims about steppe human ancestry, Indo-Iranian language and horse spread.

3. There is indeed need for further research to understand the exact nature of the rapid spread of DOM2 and other equestrian materials such as chariots. We make this note of caution in our paper: "We, however, acknowledge substantial spatiotemporal variability and evidential bias towards elite activities, so we do not discount additional, harder to evidence, factors in equine dispersal."

Agreed, however since the section regarding Indo Iranian is after this part in your paper, it seems to me as a reader as though it does not apply to the claim of indo iranian spread along with horses and chariotry. In fact, i see no caveat at all applied to this specific indo iranian and horse spread claim in your paper. It is made quite matter of factly without studying ancient horse genomes from the region of indo iranian languages.

3. ...continued We clearly show that the traditional package or horses, language and genetics does not hold together in the spread to the West, but Eastwards they are still apparently synchronous. We are careful about the exact mechanisms involved. Indeed we end by inviting further research "The results thus open up new research avenues into the historical developments of these different societal trajectories." It is likely that in some regions this was via human migrations, but in others through trade without significant patterning in human DNA patterns. Archaeologically we are challenged by the accuracy of dating. The spread appears very fast to some regions, but in fact dating methods do leave us with error margins representing multiple generations to past peoples. Thus what appears instant may have taken 100 years or more.

To me the spread of language and horses is not apparently synchronous in the region of SC asia and NW south asia. And it is also not clear what evidence is there to show that the horses are related to Sintashta culture. It is still a hypothesis according to me. I will explain below.

As I had stated in previous email, Gonur burials are carbon dated and calibrated to earlier than the Sintashta culture. Gonur has 25 human remains carbon dated and calibrated to between 2400 & 1772 calBCE. Sintashta has 16 human remains carbon dated to between 2298-1662 calBCE. More importantly, there is very minor human genetic contact between Gonur & Sintashta populations with only 2 outliers being found among 47 sampled Gonur adna. The rest of the aDna shows complete absence of steppe ancestry. Not just that, the human aDna from sites like Dzharkutan, Sapalli Tepe, & Bustan which are BMAC or post BMAC show very little steppe ancestry till 1700bce apart from a few outliers. Appearance of human steppe ancestry in Uzbekistan and Tajikistan is seen only post 1700bce in sites like Dashti Kozy and Kokcha. (all data from Narasimhan 2019) This is in contrast to European Corded ware where Yamnaya like people made a huge genetic impact and turnover.
The point that im trying to make is that this region of SC Asia which would become teeming with iranian speaking tribes was domesticating horses centuries before any human genetic (and therefore linguistic) impact from Sintashta happened. These horses could well be DOM2, or maybe not, but from some other culture rather than Sintashta or maybe through trade with Sintashta. Truthfully there is no reason to claim anything definitive without analyzing the remains from the region.

I hope that your article will reflect some of these ideas.

Thank you.

Also See

Ancient ancestral south indians (AASI) came from the east, not straight from Africa!