Animals from crucial trade route leave faintest of signatures

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Species richness from ZooMS analysis of faunal remains from habitation structures in the survey area, Image: Taylor et al. https://doi.org/10.1371/journal.pone.0205646.g010
Species richness from collagen mass fingerprinting of faunal remains from habitation structures in the survey area, Image: Taylor et al. https://doi.org/10.1371/journal.pone.0205646.g010

The Silk Road, the ancient network of trade routes that connected the East and West, is not quite paved with DNA, but researchers have found enough evidence to identify animals species important to pastoral communities based along an important stretch.

The Silk Road channeled goods, people, plants, animals, and ideas across the continental interior of Eurasia. It fueled key social developments across the Old World.

Scientists have focused their attention on a wide corridor in Kyrgyzstan between the Pamir and Alay ranges, known as the Alay Valley. The corridor, with a baseline elevation of nearly 3000 metres, was one of the primary channels of the ancient Silk Road.

Recent archaeological survey reveal a history of pastoral occupation in the region going back more than 4000 years, to the early Bronze Age, through to the Medieval period.

DNA recovered from ancient animal remains has been highly fragmented and mostly unidentifiable using traditional zooarchaeological methods, the researchers reported in the open-access peer-reviewed journal PLOS ONE.

However, they were able to identify species at several sites across the valley using a technique known as collagen mass fingerprinting (ZooMS), coupled with sex and first-generation hybrid identification through ancient DNA.

This revealed important insights into the animal economy of the early local herders.

Evidence of agropastoral occupation

The evidence pointed to a primary reliance on sheep around 2200 BCE, with cattle and goats also present.

The discovery of a large grinding stone near a Bronze or Iron Age habitation structure suggested a mixed agropastoral economic strategy, rather than a unique reliance on domestic animals.

Radiocarbon-dated work from remains recovered from later structures revealed the additional presence of domestic horses and even Bactrian camels.

The work by Max Planck Institute researcher William Taylor and his colleagues revealed that agropastoral occupation of the high-mountain Alay corridor started thousands of years before the formal establishment of the Silk Road.

In the first millennium BCE, the Trans-Eurasian system of caravan routes known as the Silk Road became one of the world’s most important channels of early globalization and transcontinental exchange, linking China with Central Asia and Europe.

By the time of the western Han Dynasty, at the end of the first millennium BCE, domestic animals — particularly horses — were exchanged in the tens of thousands from highland areas of Central Asia to the Central Plains of China.

The “blood-sweating” or “heavenly” horses from the Ferghana Valley (comprising parts of modern-day Kyrgyzstan, Uzbekistan, and Tajikistan), mentioned in Sima Qian’s historical work Shiji, were especially prized for their large size, angular build, and stamina.

In later centuries, annual trade in horses between China and Central Asia, in exchange for goods such as tea and silk, would reach into the hundreds of thousands.

The authors, discussing their findings, noted that many influential scholars have argued that the spread of pastoralism across Central Asia was likely aided by the use of horses.

Botai – Przewalski’s horse link

A key tenet of this argument was based on the assumption that horses have been used for mounted riding since around 3500 BCE, as evidenced by tooth damage to horses at the site of the Botai culture in northern Kazakhstan.

However, recent genomic research indicates that Botai horses were actually the direct ancestors of Przewalski’s horses, and were neither the progenitor of modern domestic horses nor those found in domestic contexts within the last 4000 years.

That meant the earliest direct evidence for the use of the modern domestic horse, Equus caballus, in transport now falls to the chariot burials of the Sintashta culture, around 2000 BCE, found in northern Kazakhstan and the Trans-Ural region of southern Russia.

The apparent absence of horses in other Central Asian pastoral assemblages from before 2000 BCE suggests that horse domestication may not have played a key role in the appearance of early Bronze Age pastoralists in the Alay Valley, they said.

Despite the small sample size available from the researchers’ work at later occupied sites, one apparent pattern is the regular occurrence of equid bones in features from the early through to the late Medieval period.

This, they said, sat in marked contrast to their absence in analyzed materials from earlier periods.

Discoveries from one of the sites investigated indicates that domestic horses were present in the territory of modern Kyrgyzstan by around 1600 BCE.

But it was difficult to make justifiable inferences about how horses might have been used by local residents at this time.

Mounted horsemen

“However, by the late second or early first millennium BCE, definitive evidence for mounted horseback riding in Central Asia can be found in both the archaeological and historical records.

“By the end of the first millennium BCE, military incursions to the Ferghana region by the western Han Dynasty formalized the large-scale exchange of horses between Central Asia and Chinese states, a process which continued and accelerated across the Medieval period.

“By the time of the occupation of Kyzyl-Unkur and Chegirtke Canyon, the Alay Valley was already an artery of the Silk Road and a major trade corridor, one in which horses may have been key as both a prized commodity as well as a means of traveling and exchanging goods along the mountain corridors of the Pamir, Alay, and Tien Shan.

“Other equids, particularly donkeys, are also known to have played a crucial role in the transport networks of Silk Road Central Asia due to their stamina and low water requirements.

“Nonetheless, our DNA results indicate that all identified equids in the present study were female domestic horses. In contrast to stallions and geldings, commonly preferred as battle mounts, mares are more docile and easily controlled.

“In historical records, mares were often preferred by Mongol cavalry on long journeys because of the added sustenance that could be gleaned from the animal’s milk.

“The consistent presence of female horses in the small assemblage of analyzed Alay sites may relate to their use in long-distance transport across the ancient Silk Road.”

At two sites, mares may have also played a role in subsistence, particularly for the production of kymyz (fermented mare’s milk) that remains popular in the Alay region today.

In conclusion, they said their results revealed that the Alay Valley, one of the most important geographic corridors of interior Central Asia and a major artery of the historic Silk Road, was occupied by pastoralists or mixed agropastoralists by the early Bronze Age, during the late 3rd millennium BCE.

The techniques used had enabled a clearer view of the subsistence choices of ancient peoples in the region, they said.

“When considered in chronological context alongside other early Bronze Age archaeological contexts from montane Central Asia, our results suggest that, contrary to some hypotheses, horses did not likely play a role in the genesis of pastoral lifeways in southern Kyrgyzstan during the Bronze Age, at least as a dietary resource.

“Instead, the ancient herding economy seems to have focused largely on sheep, supplemented by cattle and goat, and perhaps agricultural activity — much as it remains today.

“Following the development of mounted riding and the formation of the Silk Road, both horses and camels may have increased in economic significance.”

Horses were both transport animals and a trade commodity, which may explain their increased visibility in some of the Alay archaeological assemblages.

The findings paint a picture of a rich and multi-millennial history of domestic animal use in the Alay Valley, and suggest that the development of horse transport and the formation of transcontinental exchange networks had a key influence on the economic choices of high-mountain herders in the continental interior.

Taylor W, Shnaider S, Abdykanova A, Fages A, Welker F, Irmer F, et al. (2018) Early pastoral economies along the Ancient Silk Road: Biomolecular evidence from the Alay Valley, Kyrgyzstan. PLoS ONE 13(10): e0205646. https://doi.org/10.1371/journal.pone.0205646

The study, published under a Creative Commons License, can be read here

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