Afghanistan, Once Upon A Time

There was a Greek kingdom in Afghanistan and surrounding parts of Central Asia, called the Greco-Bactrian Kingdom, for roughly 136 years from 256 BCE until 120 BCE.

Ethnic Turkish Expansion

Razib Khan has been publishing a three part series on the genetics and human population history of Anatolia on his Unsupervised Learning platform. His latest, on how Anatolia became Turkish is here and opens with the useful summary map below. 

The site is worth subscribing to, if you have the time for it, and the quality is, as usual, first rate: artfully written and informed by Razib's wide historical, linguistic and genetic knowledge. I agree pretty much 100% with the narrative told by the map below.

Turkish invaders ca. 1100 CE (a quite accurate estimate, more specifically, it is historically attested to have happened in 1071 CE) led to language shift in Anatolia, even though genetic estimates are that these invaders account for only perhaps 8%-20% of modern Turkish genetic ancestry (probably closer to the low end of that range). Their expansion was a classic case of expanding herder tribes confronting sedentary farmers.

Turkish expansion predates the Mongolian Empire and postdates by centuries, the Bronze Age. Their expansion was arguably the last of a series of sweeps east to west and west to east across the general region of roughly comprised of the Pontic Caspian steppe, Central Asia and Siberia that persisted. The Mongolian Empire left only a weak trace after it collapsed, but one could arguably call Russian expansion to the east the last sweep.

A Principal Component Analysis Of Major Branches Of Eurasian Population Genetic Diversity

Via Razib Khan.

This chart is a two dimensional chart of the relative genetic similarities and relationships of many modern and one group of ancient Eurasian populations from a paper analyzing the genetics of the Saami people of Northern Scandinavia (especially Finland with which they have the strongest linguistic ties), who are now herders and historically were one of the last hunter-gatherer populations of Europe.

Inbreeding Declined In West And Central Eurasia During The Holocene Era

A new paper published in the journal Cell shows that inbreeding has declined over the last 12,000 years, as demonstrated with 411 ancient DNA samples from West Eurasia (defined as Europe) and Central Eurasia (defined as Southwest Asia, the Caucasus and Central Asia).

Extreme consanguineous matings did occur among agriculturalists but were rare, while inbreeding was more common in hunter-gatherers and declined more gradually as farming societies grow more complex. Modern Europe, which has far more people, has even less inbreeding.

The regressions and images above go from the present on left, to the past, on the right. F(ROH) (for runs of homozygosity) is a measure of inbreeding with a higher number indicating more inbreeding in the lineage of the individual whose DNA is examined.

Essentially, the larger the size of the communities involved, as improving food production technology makes possible, the less inbreeding is found.

The detailed numerical data is summarized in the chart below. The key data points (with median F(ROH)) are:

* Hunter-gathers (N=40) 0.0633

* Simple agriculturalists (N=102) 0.0286

* Early complex agriculture (N=230) 0.0250

* Advanced complex agriculture (N=160) 0.0160

* Modern Central Eurasia (N=309) 0.0156

* Modern Europe (N=139) 0.0039

Central Eurasia is less inbred than Europe among hunter-gathers, simple agriculturalists, and advanced complex agricultural societies, but is modestly more inbred in the era of early complex agriculture, although the statistical significance of the differences in these areas is modest.

In the modern era, Central Eurasia with an inbreeding coefficient of 0.0156 (which is more than in Central Eurasia during the advanced complex agriculture phase) is much more inbred than modern Europe which has an inbreeding coefficient of 0.0039. The combined modern inbreeding coefficient is 0.0066.

Prevalence Of Moderate Inbreeding With Some Cousin Marriage

100% of hunter-gatherers, 95% of farmers prior to the advanced complex agriculture phase, 77% of farmers in an era of advanced complex agriculture, and 14% of modern Europeans are as inbred as the median modern Central Eurasian (0.0117). This is what one would expect to arise from endogamy within a community with some cousin marriage (including remote cousins) that is not predominant.

Prevalence Of Cousin Marriage

93% of hunter-gatherers, 5-15% of ancient farmers, and 2% of modern Europeans are as inbred as 23% of modern Central Eurasian are (0.0391), a level typical for first cousin marriages. According to the paper:

Samples from modern groups like the Balochi, the Bedouin, or the Sindhi from Pakistan have the highest proportions of individuals with FROH > 0.0391 (50%, 41.3%, and 33.3% respectively).

Prevalence Of Highly Inbred Mating

10% of hunter-gathers, 1.9% of simple agriculturalists and modern Central Eurasians, 0.4% of farmers in early complex agriculture, and 0% of farmers in advanced complex agriculture and modern Europeans has an inbreeding coefficient of 0.0932. 

This is a level of inbreeding in excess of otherwise unrelated double cousin marriages, and similar to that of marriages between an uncle or aunt and that person's niece or nephew, between half-siblings, between a grandparent and a grandchild, or offspring of closer matings. 

Even remote cousin over many generations in a small community, however, can elevate the inbreeding coefficient of mere cousin marriages or of a double cousin marriage, above this threshold. The genetic evidence indicates that this sort of genetic drift was involved in the early hunter-gatherer communities, while cousin and/or closer marriage was a major factor in other genomes studied.

The high inbreeding coefficients in modern "Central Asians" are largely a product of Islamic law's acceptance of cousin marriage and of traditional cultures in some (but not all) Islamic societies, that favor high rates of cousin marriage of 10% to more than 50%, as shown on the map below. 

Cousin marriage is uncommon, however, despite being at least nominally legal under Islamic law, in countries that are predominantly Muslim where Muslims predominantly follow the school of Sunni Islamic jurisprudence that is predominant in Southeast Asia (i.e. the Shafi'i school of Sunni Islamic law).

Some concluding comments of the paper bear repeating in their entirety so as not to lose the nuance of these important caveats to its findings:

Three points further deserve mention regarding mating patterns in human societies. 

One is the seeming contrast between the high levels of drift-driven autozygosity (panmictic inbreeding) we report for ancient hunter-gatherer societies and ethnographic studies showing low levels of inbreeding among modern-day hunter-gatherers. For instance, a comparison of inbreeding patterns in a worldwide sample of contemporary hunter-gatherers with Amazonian horticulturalists reported lower inbreeding in hunter-gatherer groups. Hill and colleagues also report low levels of relatedness within modern-day hunter-gatherer bands. However, the mentioned ethnographic findings rely on genealogies and report the prevalence of inbreeding by consanguinity, not inbreeding by drift. In fact, we also find consanguinity to be rare among early Holocene Eurasian hunter-gatherers relative to agriculturalists, consistent with widespread exogamy in modern-day hunter-gatherers. This raises the possibility that reciprocal exogamy and consanguinity avoidance traditions may have been predominant among human foragers since prehistory (but possibly not in archaic hominins).

Second, our results lend support, albeit with limited data, to the hypothesis that extreme consanguinity may have become more common with farming. This result parallels higher within-group marriages among modern-day horticulturalists than foragers. It is also consistent with singular reports on ancient agriculturalist genomes, such as evidence for consanguinity identified in an early Neolithic farmer from Iran, a first-degree incest case from Neolithic Ireland, as well as a recent report on close-kin unions in the central Andes after 1000 CE. 

In our analysis, among the seven individuals with the highest level of inbreeding (with FROH > 0.125), all four hunter-gatherers appear autozygous by drift, while all three agriculturalists appear autozygous by consanguinity. This appears unlikely to happen by chance (Fisher’s exact test, two-sided p = 0.029). These results are consistent with the view that consanguineous traditions could have thrived in class-based agricultural societies with private property more readily than in more egalitarian hunter-gatherer groups.

Finally, we report higher consanguinity in Central versus West Eurasia in contemporary societies, in parallel with earlier work. This is consistent with widespread first- or second-cousin marriage practices in agricultural societies in Middle Eastern and North African countries and in South Asia, including Muslim and Jewish groups, as documented by ethnographic or genomic studies. We note that cousin marriages were also common among royal dynasties and upper classes of Europe until the 20th century, and many prominent European scientists of that period are known to have married their first cousins, including Charles Darwin and Albert Einstein. These traditions are thought to have arisen through various social factors, including the inheritance of property in class societies.

Interestingly, we do not observe the relatively high rates of consanguineous marriage observed in modern-day Central Eurasia in any of the past societies we studied, in Antiquity or earlier. We naturally prefer to remain cautious, especially given the limited sample size of our advanced complex agriculturalist samples from West and Central Eurasia (n = 9 and n = 30, respectively). Nevertheless, it appears possible that present-day cultural patterns may have emerged relatively late in time.

Responding To The 5.2 Kya Event In Anatolia

There aren't many studies demonstrating the impact of the 5.2 kiloyear climate event on historic communities of people, in part, because the civilizations impacted by it at the Neolithic-Copper Age transition didn't have the same scale of urban areas, empires, architecture and sophisticated goods to collapse from, and writing was much more limited then, making the impact less obvious. 

But this study deserves kudos for using clever methods to observe these subtle impacts on human communities on a quite fine grained time scale which other methods can't always resolve nearly as finely.

Just as the 4.2 kya event was pivotal in ushering in the Bronze Age and creating a political vacuum into which Indo-Europeans could expand in Europe, Central Asia and South Asia, the 5.2 kya event was pivotal in creating a political vacuum in Neolithic society into which copper age cultures could expand. 

This (or the 5.9 kya event) is probably the climate event that was the proximate cause of the demographic transition from the Sardinian-like Anatolian first farmers of the Fertile Crescent Neolithic Revolution to copper age people with a different genetic makeup who migrated to Anatolia from elsewhere in the West Asian highlands who partially replaced them in Anatolia.

It is also one of the first documented iterations of a pattern that would repeat itself many times in history. When rain is ample and temperatures are comfortable, agriculture flourishes and sophisticated sedentary civilizations arise. When drought strikes and it gets too hot or too cold, herding civilizations replace the farming civilizations that flourished in better times.

"People would build a mud brick structure, and over the years the structure is either abandoned or collapses and the people just build on top of it," Smith says. "Eventually these villages look like they have been built on hills, but they're really just occupations going up and up."

Just as the occupants built new layers up, the archaeologists excavate down to get a glimpse of history and how lives changed over the millennia. Within the layers, archaeobotanists like von Baeyer and Smith look for ancient plant remains; for instance, intentionally or unintentionally charred plant matter. Though wood was often used, much can be learned by looking at the remains of fires fueled by livestock dung, says Smith: "The dung contains seeds that give clues about what the animals were eating." 

. . .

The focus was on a time period called the Late Chalcolithic, roughly 3700-3200 years before the common era (BCE). By referencing paleo-climatic data and Steadman's very detailed phasing at Çadır Höyük, the researchers were able to discern how lifestyles changed as the climate rapidly shifted in what is called the 5.2 kya event, an extended period of aridity and drought at the end of the fourth millennium BCE.

With climate change, there are lots of strategies that can be used to adapt says Smith, "They could have intensified, diversified, extensified, or abandoned the region entirely. In this case they extensified the area of land used and diversified the herds of animals they relied upon."

Zooarchaeologists on the site examined the bones to further demonstrate the shift in the types of animals herded, while the seeds from the dung-fueled fires at the dig site gave clues to what the animals were eating.

Smith says, "We know they were herding cattle, sheep, goats, and pigs, and we saw a shift to animals that are grazers. They all have a different diet, and by diversifying you are maximizing the range of potential calories that can eventually be consumed by humans."

By employing this mixed strategy, the people of Çadır Höyük were ensuring their survival as the climate became increasingly dry. Smith says that at the same time they continued to grow wheat, barley, chickpeas, and lentils, among other crops for humans, while the animals grazed on crops not suitable for human consumption -- a strategy to maximize resources and resilience.

From here. The paper and its abstract are as follows:

This study examines how the population at Çadır Höyük on the north central Anatolian plateau modified agricultural and fuel use practices in response to rapid social and environmental change between 3600 and 2900 BCE (Late Chalcolithic and Transitional to Early Bronze periods). 

Using descriptive and multivariate statistics to explore data from 60 archaeobotanical samples spanning three periods of occupation (3600–3200 BCE, 3300–3100 BCE, and 3100–2900 BCE) the results reveal that the inhabitants of Çadır relied heavily on barley, emmer, lentils, and flax throughout the Late Chalcolithic. Both dung and wood were used as fuel, although dung fuel appears to have been preferentially used. 

The most significant change throughout this period was a shift from foddering animals to grazing animals on the steppe. This shift corresponded with the 5.2 kya event, a period of increased aridity at the very end of the 4th millennium BCE. By diversifying their agricultural strategies to more risk adverse practices, the population at Çadır demonstrated their ability to be resilient in the face of climate change.

Madelynn von Baeyer, Alexia Smith, Sharon R. Steadman. "Expanding the plain: Using archaeobotany to examine adaptation to the 5.2 kya climate change event during the Anatolian Late Chalcolithic at Çadır Höyük." 36 Journal of Archaeological Science: Reports 102806 (2021). DOI: 10.1016/j.jasrep.2021.102806

Why Are Anatolian and Tocharian Languages The Most Divergent Indo-European Languages?

It is widely agreed that Anatolian and Tocharian are the most divergent Indo-European languages and the conventional view is to attribute this to a greater time depth of divergence from Proto-Indo-European.

The divergences are, in my humble opinion, not primarily due to time depth. 

(Note that this post expands upon a comment to this post at Gene Expression).

General Considerations In Historical Linguistics and Language Evolution

The naive mutational variation accumulation over time model of language divergence greatly overestimates that importance of that component of language change, which is actually much slower, and ignores the central role played by language contact.  See, e.g., the overview here.

One example of that is Icelandic, which was until very recent times when telecommunications and air travel became available, the closest of the Germanic languages to Old Norse (which is basically proto-Germanic), mostly because it had less contact with other languages due to its isolation at the frontier. See, e.g., here,

Another example is that phonetically, the Appalachian accent is the closest modern dialect of English to the Elizabethan English of Shakespeare, again, due to low levels of contact with other dialects of English. 

Likewise, the New Zealand accent was until recently more conservative of 19th century British dialect than modern British English, while adopting some Maori substrate words for concepts it didn't have words for and being influenced by contact with the Australian dialect.

Low population sizes also reduce mutational change in all of these case.

Also, language divergence actually tends to be punctuated:

We used vocabulary data from three of the world's major language groups—Bantu, Indo-European, and Austronesian—to show that 10 to 33% of the overall vocabulary differences among these languages arose from rapid bursts of change associated with language-splitting events. Our findings identify a general tendency for increased rates of linguistic evolution in fledgling languages, perhaps arising from a linguistic founder effect or a desire to establish a distinct social identity.

The divergence between Old English and Middle English, for example, is largely due to the singular impact of French Norman influence on the language after the Norman Conquest of England, in the common case of language change due to emulation of elite dialects (one of the most common sources of homogenization of language in a region). 

Language replacement scenarios also usually involve strong substrate influences (e.g. the quirks of the South Asian dialects of English) especially for words with no superstrate language counterpart like local botany words. 

It is also often the case that simplifications of language structure due to mass language learner effects. But see this paper reviewing this hypothesis critically.

The differences in American English from British English, in contrast, reflect another common punctuated influence, where a community of people deliberately exaggerate local dialect differences in order to create shibboleths that expose outsiders and to distinguish themselves culturally from a community that they are alienated from.

Language contact usually has mostly lexical impact (i.e. loan words), but also can give rise to other areal and contact language features (like the sentence closing term “lah” in Malaysian and Singaporian dialects derived from Arabic traders), and sometimes place names (e.g. Punic place names in Britain and Ireland).

Distinct Indo-European Substrates

The other key point is that in almost all of the Indo-European language family’s European ranges, hunter-gatherer languages were extinct or all but extinct, and the substrate first farmer languages shared a descent from the language family of Western Anatolian farmers (probably in two main subfamilies, one for Linear Pottery Farmers in the Danubian basis and point north, and the other for the Cardial Pottery Farmers of the Mediterranean coast). See also here and here.

As societies lacking metal and horses, these Neolithic first farmers of Europe also had fairly low population density (even though it was 100x that of terrestrial hunter-gatherers), so due to low population density and frontier status, the amount of divergence between the first European Neolithic farmers and the struggling farmer societies a couple of thousand years later when Indo-Europeans filled a vacuum was probably modest.

This shared substrate over so many Indo-European subfamilies no doubt hides the extent of Anatolian Neolithic language family substrate influence in them. See, e.g., here (reviewing Bronze Age outlines of Indo-European expansion in Europe). But not all Indo-European language families shared this substrate.

Why Are Tocharian Languages Divergent?

Tocharian is divergent because it is the purest of the descendants of Indo-European, because they had virtually no substrate influence or language contact, were on a frontier, and weren’t a particularly large language community despite fairly high population density, because it was geographically constrained to a handful of towns, rather than being divergent due to its great antiquity. 

Notably, J.P. Mallory, one of the leading Tocharian scholars, came around in about 2012 to the view that the Tarim basin civilization isn’t all that old, based upon archaeological evidence stating:

[T]here is really no serious evidence for arable agriculture (domestic cereals) east of the Dnieper until after c. 2000 BCE (see also Ryabogina & Ivanov 2011; Mallory, in press:a). This means that there is also no evidence for domestic cereals in the Asiatic steppe until the Late Bronze Age (Andronovo etc). From the perspective of the Pontic-Caspian model, the ancestors of the Indo-Iranians and Tokharians should not cross the Ural before c. 2000 BCE at the very earliest. Hypotheses linking the Tokharians to earlier eastward steppe expansions associated with the Afaasievo or Okunevo cultures of the Yenisei or Altai (Mallory and Mair 2000) become very difficult if not impossible to sustain (as long as there is no evidence of arable agriculture in these cultures) as Tokharian retains elements of the Indo-European agricultural vocabulary.

– J. P. Mallory, “Twenty-first century clouds over Indo-European homelands” (Conference Presentation in Moscow, September 12, 2012).

Mallory made the case in a 2011 talk that R1b was a Tocharian genetic signature based upon West Eurasian Y-DNA haplogroups found in Uyghur populations that were direct successors to and brought about the fall of the Tocharians during a period of Turkic expansion. There is also R1b in Iron Age ancient DNA east of the Tarim basin from what appears to be a related West Eurasian culture. But, ancient Tarim mummy DNA from ca. 1800 BCE, analyzed in 2009 showed uniformly R1a1a Y-DNA haplogroups (citing Li, Chunxiang, et al., “Evidence that a West-East admixed population lived in the Tarim Basin as early as the early Bronze Age” BMC Biology (February 17, 2010)).

Not exactly on point but relevant is that Tocharian cemeteries contained ephedra, a commonly hypothesized botanical extra drug to be the active ingredient in Indo-Iranian Soma/Homa. Tocharian culture also has primitive antecedents of physical culture attributes (e.g. basic Tartan weaves) typically associated with Celtic culture.

The Case For A Young Origin For Anatolian Languages

In the case of the Anatolian languages, in contrast, strong contact with a highly divergent substrate from the Anatolian Farmer substrate of Europe is what explains its divergence.

In the early metal ages, the Hattic language and civilization (probably derived from metal using civilizations of the Caucasus mountains and Zargos mountains in a language family that may have also included Hurrian and is probably modest strongly related to one or more of the modern Caucasian languages), spread across Anatolia replacing the Anatolian farmer language. There is suggestive evidence that the Minoan language was also from the same language family (e.g. the phonetic structure of the two languages, recorded in the Minoan case by Eto-Cretian inscriptions and Egyptian phonetic records of Minoan incantations).

Documentary and archaeological evidence, however, suggest that the Hittites occupied only a few towns in a sea of Hattic people ca. 1800 BCE, before their dramatic expansion, roughly contemporaneous with the appearance and expansion of the Mycenaean Greeks (the first Aegean people to speak Indo-European languages), and while there are many Anatolian languages attested, all but a couple have the relationship of the Romance language to Latin with Hittite, and the couple of earlier ones are not attested significantly earlier than the Hittite language. Iron use and cremation were important litmus tests of Anatolian Indo-Europeans that are corroborated with documentary evidence and archaeological evidence in the post-1800 BCE time period. I review some of that evidence here. See also here.

It also isn’t clear how much of the Anatolian languages were elite imitation driven (compare Hungarian ca. 1000 CE which results in language shift without much demic impact), and how much was due to population replacement/introgression. 

The frequency of R1b in modern Anatolian samples suggests a significant demic component, but is complicated by the multilayered palimpsest of periods in Anatolian history and prehistory including Hellenic sourced migration into Anatolia, and a period of Iranian steppe migration into the Levant, at least partially through Anatolia (See also here).

So, how do the Anatolian languages grow so divergent?

The grow divergent because the Hattic substrate in which they were immersed (to the extent that it influenced their choice of proper names and that Hattic remained a liturgical language in the Hittite empire centuries after it ceased to be used in daily life, like liturgical relicts of ancient Hebrew, ancient Latin, ancient Sumerian, and Coptic), was profoundly different from that of the Anatolian Neolithic farmer substrate in Europe or the Harappan substrate in Sanskrit (which may be shared by all Indo-Iranian languages, as BMAC was in the Harappan sphere of influence and both Harappan and BMAC languages may be derived at great time depth from the Caucasian Neolithic first farmer substrate). 

Copper age/early Bronze Age Hattic culture and language (like Copper Age/early Bronze Age Harappan culture) also had more staying power and influence than stone age European Neolithic culture because more advanced civilizations had more populations density and couldn’t just be trampled into oblivion by Indo-European successors. 

My suspicion is that pre-Indo-European conquest acquisition of metallurgy also was important in allowing Basque and related Vasconic languages to survive Indo-European obliteration. (See also here and here and here and here and here).

We don’t have enough Hittite, other Anatolian language speaker, and Hattic ancient DNA to confirm an appearance of steppe ancestry around 1800 BCE and its absence before then in Anatolia, but we also have no ancient or modern DNA evidence that isn’t a good fit to that hypothesis.

A Footnote On Armenian 

In the same vein, Armenian is hard to classify because it has mixed influences for different neighboring Indo-European language families, with Greek influence competing, for example, with Slavic and Indo-Iranian language influence. Armenian is attested in writing only in the mid- to late Iron Age, so a whole stew of diverse Indo-European linguistic influences is hard to parse out.

Buddhist Origins In One Map

 

Drought Destroyed River Civilizations In The Turan Before The Mongols Arrived

One emerging repeated pattern in history is that climate destroys a civilization and then, after a civilization is already in its death throes, "barbarians" rush in to fill the vacuum, while famine begets plagues as well. A few of many examples make the point.

It happened in the Indus River Valley Civilization, Mesopotamia, Egypt, the Levant around 2000 BCE that also was pivotal in further Indo-European expansion into Europe. 

There were parallel events of this type in East Asia and Southeast Asia (both island and mainland). 

It happened with Bronze Age collapse in the Mediterranean basin and Europe around 1200 BCE. 

The fall of the Roman Empire was, in part, to due climate issues. 

This happened to the Ancient Puebloans around 1000 CE and related event also pushed Na-Dene peoples out of Canada and into what became the American Southwest severely impacting tribal civilizations with Meso-American roots like the Utes.

Something along these lines facilitated the dramatic Mongol Empire expansion by destroying Central Asian river civilizations (which you'd probably never even heard of) of a region also known as the Turan, clearing the way for barbarian invasions in the late Middle Ages, and that is the subject of a new paper on the subject in PNAS.

While Genghis Khan and Mongol invasion is often blamed for the fall of Central Asia's medieval river civilizations, new research shows it may have been down to climate change. Researchers conducted analysis on the region and found that falling water levels may have led to the fall of civilizations around the Aral Sea Basin, as they depended on the water for irrigation-based farming. . . .

"We found that Central Asia recovered quickly following Arab invasions in the 7th and 8th centuries CE because of favourable wet conditions. But prolonged drought during and following the later Mongol destruction reduced the resilience of local population and prevented the re-establishment of large-scale irrigation-based agriculture."

The research focused on the archaeological sites and irrigation canals of the Otrar oasis, a UNESCO World Heritage site that was once a Silk Road trade hub located at the meeting point of the Syr Darya and Arys rivers in present southern Kazakhstan.

The researchers investigated the region to determine when the irrigation canals were abandoned and studied the past dynamics of the Arys river, whose waters fed the canals. The abandonment of irrigation systems matches a phase of riverbed erosion between the 10th and 14th century CE, that coincided with a dry period with low river flows, rather than corresponding with the Mongol invasion.

Via Science Daily. 

The paper and its abstract are as follows:

Our paper challenges the long-held view that the fall of Central Asia’s river civilizations was determined by warfare and the destruction of irrigation infrastructure during the Mongol invasion. An integration of radiometric dating of long-term river dynamics in the region with irrigation canal abandonment shows that periods of cultural decline correlate with drier conditions during multicentennial length periods when the North Atlantic Oscillation had mostly positive index values. There is no evidence that large-scale destruction of irrigation systems occurred during the Arab or Mongol invasion specifically. A more nuanced interpretation identifies chronic environmental challenges to floodwater farming over the last two millennia, punctuated by multicentennial-length periods with favorable hydromorphic and hydroclimatological conditions that enabled irrigation agriculturists to flourish.

Abstract

The Aral Sea basin in Central Asia and its major rivers, the Amu Darya and Syr Darya, were the center of advanced river civilizations, and a principal hub of the Silk Roads over a period of more than 2,000 y. The region’s decline has been traditionally attributed to the devastating Mongol invasion of the early-13th century CE. 

However, the role of changing hydroclimatic conditions on the development of these culturally influential potamic societies has not been the subject of modern geoarchaeological investigations. In this paper we report the findings of an interdisciplinary investigation of archaeological sites and associated irrigation canals of the Otrār oasis, a United Nations Educational, Scientific and Cultural Organization (UNESCO) World Heritage site located at the confluence of the Syr Darya and Arys rivers in southern Kazakhstan. This includes radiometric dating of irrigation canal abandonment and an investigation of Arys river channel dynamics. 

Major phases of fluvial aggradation, between the seventh and early ninth century CE and between 1350 and 1550 CE coincide with economic flourishing of the oasis, facilitated by wet climatic conditions and higher river flows that favored floodwater farming. Periods of abandonment of the irrigation network and cultural decline primarily correlate with fluvial entrenchment during periods of drought, instead of being related to destructive invasions. Therefore, it seems the great rivers of Central Asia were not just static “stage sets” for some of the turning points of world history, but in many instances, inadvertently or directly shaped the final outcomes and legacies of imperial ambitions in the region.

Toonen, W.J.H., et al., "A hydromorphic reevaluation of the forgotten river civilizations of Central Asia." Proceedings of the National Academy of Sciences, (2020) DOI: 10.1073/pnas.2009553117

Northern Route Migration

Assuming that humans dispersed into Asia predominantly via a southern coastal route is firmly rooted in conventional wisdom. But, the evidence is far more equivocal on the question. 

Northern and Central Asia have been neglected in studies of early human migration, with deserts and mountains being considered uncompromising barriers. However, a new study argues that humans may have moved through these extreme settings in the past under wetter conditions. By analyzing past climate, northern Asia emerges as a potential route of human dispersal, as well as a zone of potential interaction with other hominins such as Neanderthals and Denisovans.

From here.

Feng Li, Nils Vanwezer, Nicole Boivin, Xing Gao, Florian Ott, Michael Petraglia, Patrick Roberts. "Heading north: Late Pleistocene environments and human dispersals in central and eastern Asia." PLOS ONE, 2019; 14 (5): e0216433 DOI: 10.1371/journal.pone.0216433