Who We Are And How We Got Here - Part 4 - India
The Indian subcontinent is a patchwork quilt of cultures, languages and genetics
In many ways, the history of the Indian subcontinent parallels that of Europe, which is also a subcontinent of Asia. In both cases an indigenous population which consisted of a mixture of farmers and hunter-gatherers was impacted genetically and culturally by warlike migrants from the steppe who established highly stratified and unequal societies sometime between four and five thousand years ago (c. 2000 to 3000 BCE).
The great Himalayas were formed around ten million years ago by the collision of the Indian continental plate, moving northward through the Indian Ocean, with Eurasia. India today is also the product of collisions of cultures and people.
Consider farming…Indian farming today is born of the collision of the two great agricultural systems of Eurasia. The Near Eastern winter rainfall crops, wheat and barley, reached the Indus Valley sometime after nine thousand years ago according to archaeological evidence…Around five thousand years ago, local farmers succeeded in breeding these crops to adapt to monsoon summer rainfall patterns, and the crops spread into peninsular India. The Chinese monsoon summer rainfall crops of rice and millet also reached peninsular India around five thousand years ago. India may have been the first place where the Near Eastern and the Chinese crop systems collided.
Language is another blend. The Indo-European languages of the north of India are related to the languages of Iran and Europe. The Dravidian languages, spoken mostly by southern Indians, are not closely related to languages outside South Asia. There are also Sino-Tibetan languages spoken by groups living in the mountains fringing the north of India, and small pockets of tribal groups in the east and center that speak Austroasiatic languages related to Cambodian and Vietnamese, and that are thought to descend from the languages spoken by the peoples who first brought rice farming to South Asia and other parts of Southeast Asia…The people of India are also diverse in appearance, providing a visual testimony to mixture. A stroll down a street in any Indian city makes it clear how diverse Indians are…” (p. 127)
Researchers determined that the modern inhabitants of the Indian subcontinent are a mixture of two genetically distinct populations.
One was a native branch originating from the first migrants to the Indian subcontinent from Africa as determined by mitochondrial DNA. Another was a population closely related to the West Eurasians who possessed up to 50 percent Yamnaya-related ancestry. All Indians living today are some proportion of mixture between these two groups. There are no "pure" Indians, with the lone exception of the inhabitants of the Andaman Islands—a small, remote archipelago in the Bay of Bengal—who were used to establish the DNA profile of the original inhabitants of prehistoric India.
The researchers named these two ancestral groups the Ancestral North Indians (ANI) and the Ancestral South Indians (ASI).
The term Ancestral North Indian was chosen partly for political reasons. Although the ANI were closely related to West Eurasians, it was deemed politically explosive to imply that Indian culture traces its origins to somewhere outside the Indian subcontinent (especially with the rise of Hindu nationalism). It also had uncomfortable resonance with Nazi racial ideology which depicted a “superior” group of light-skinned invaders conquering and enslaving a larger population of "inferior" dark-skinned people. The Nazis even appropriated the term "Aryan" to refer to themselves and the Swastika—a traditional Indian good luck symbol—as their emblem.
Given that the exact geographic origin of this northern population was unknown, it was deemed most politically appropriate to refer to them simply as Ancestral North Indians—a term which gave no indication as to where this population originated; a fact which could not be determined with certainty in any case.
We wrote that the people of India today are the outcome of mixtures between two highly differentiated populations, "Ancestral North Indians" (ANI) and "Ancestral South Indians" (ASI), who before their mixture were as different from each other as Europeans and East Asians are today.
The ANI are related to Europeans, central Asians, Near Easterners, and the people of the Caucasus, but we made no claim about the origin of their homeland or any migrations. The ASI descend form a population not related to any present-day populations outside India.
We showed that the ANI and ASI had mixed dramatically in India. The result is that everyone in mainland India today is a mix, albeit in different proportions, of ancestry related to West Eurasians, and ancestry more closely related to diverse East Asian and South Asian populations. No group in India can claim genetic purity...we found that West Eurasian-related mixture in India ranges from as low as 20 percent to as high as 80 percent...No group is unaffected by mixing, neither the highest nor the lowest caste, including the non-Hindu tribal population living outside the caste system. (pp. 135-136)
Although geneticists made no claim about their origins, many archaeologists trace the origins of Indo-Iranian culture and languages to a group known as the Sintashta-Petrovka culture, which inhabited the Eurasian steppe between 2200 and 1800 BCE. The earliest known chariots have been found in Sintashta burials. This steppe culture was also notable for its extensive practice of bronze and copper metallurgy.
Genetic studies showed them to be related to the Corded Ware people in Eastern/Central Europe, suggesting that they were an eastward migration of the Corded Ware culture. Sintashta culture was succeeded by the Andronovo culture which existed between 2000 to 900 BCE. Archaeologists have noted clear similarities between the burial rituals of the Andonovo culture and those outlined in the Rig Veda—the earliest Indian religious text. Cultural and linguistic connections have also been noted with Scandinavian Bronze Age cultures.
Chariot Racers of the Steppes (Discover Magazine)
The researchers found a correlation between genetics and language, with higher amounts of ANI ancestry where Aryan (Indo-European) languages are spoken in India today, and higher amounts of ASI ancestry where Dravidian languages are spoken, indicating that these were probably the original native languages of these two groups. They also found that groups placed higher in the Indian caste system had more ANI ancestry than those placed lower in the caste system: "...the findings...suggest that the ANI-ASI mixture in ancient India occurred in the context of social stratification." (p. 137)
By studying the relative sizes of stretches of ANI and ASI ancestry in the chromosomes of modern Indians, researchers were able to estimate a date for when this admixture occurred. The dates they came up with were sometime between 4,000 and 2,000 years ago. Thus, the mixing of ASI and ANI must have taken place within this roughly two thousand year window. Somewhat counterintuitively, the earliest admixture was detected in southern populations, with more recent admixture happening in northern populations. To explain this phenomenon, researchers hypothesized that the earliest mixed populations would have migrated southward, while mixing would have continued to occur along the original interaction zone in the north.
We found that all Indian groups we analyzed had ANI-ASI mixture dates between four thousand and two thousand years ago, with Indo-European speaking groups having more recent admixture dates on average than Dravidian-speaking groups.
The older mixture dates in Dravidian-speaking groups surprised us. We had expected that the oldest mixtures would be found in the Indo-European speaking groups of the north, as it is presumably there that the mixture first occurred. We then realized that an older date in Dravidians actually makes sense, as the present-day locations of people do not necessarily reflect their past locations.
Suppose that the first round of mixture in India happened in the north close to four thousand years ago, and was followed by subsequent waves of mixture in northern India as previously established populations and people with much more West Eurasian ancestry came into contact repeatedly along a boundary zone. The people who were the products of the first mixtures in northern India could plausibly, over thousands of years, have mixed with or migrated to southern India, and thus the dates in southern Indians today would be those of the first round of mixture. Later waves of mixture of West Eurasian-related people into northern Indian groups would then cause the average date of mixture estimated in northern Indians today to be more recent than in southern Indians.
A hard look at the genetic data confirms the theory of multiple waves of ANI-related mixture into the north. Interspersed among the short stretches of ANI-derived DNA we find in northern Indians, we also find quite long stretches of ANI-derived DNA, which must reflect recent mixtures with people of little of no ASI ancestry.
Remarkably, the patterns we observed were consistent with the hypothesis that all of the mixture of ANI and ASI ancestry that occurred in the history of some present-day Indian groups happened within the last four thousand years. This meant that the population structure of India before around four thousand years ago was profoundly different from what it is today. Before then, there were unmixed populations, but afterward, there was convulsive mixture in India, which affected nearly every group. (pp. 139-140)
After 2016, genetic studies of Near Eastern farming populations found a genetic relationship between the people of India and prehistoric farming peoples who inhabited the Iranian plateau. It was further discovered that this Iranian farmer ancestry was present in both Ancestral North Indians and Ancestral South Indians. This suggested that the farming/herding cultures of ancient Iran must have migrated into India at some point and left a genetic signature in both of these ancestral populations.
The Ancestral South Indians, then, were not a pure aboriginal population after all; but rather a mixture of Iranian farmers and native Indian hunter-gatherers. The Ancestral North Indians were a mixture of Iranian farmers and West Eurasian steppe peoples.
Just as the Early Anatolian Farmers migrated east and introduced farming into Europe, the early Iranian farmers headed west and brought farming into India. Then, at some later period, horse-riding nomadic pastoralists from the Pontic-Caspian steppe swept into both regions sometime around 4000 and 5000 years ago and contributed significant portions of ancestry—especially male ancestry— to both subcontinents, along with culture and language.
Our finding that both the ANI and ASI had large amounts of Iranian-related ancestry meant that we had been wrong in our original presumption that one of the two major ancestral populations of the Indian Cline had no West Eurasian ancestry. Instead, people descended from Iranian farmers made a major impact on India twice, admixing both into the ANI and the ASI.
...The ANI were a mixture of about 50 percent steppe ancestry related distantly to the Yamnaya, and 50 percent Iranian farmer-related ancestry from the groups the steppe people encountered as they expanded south.
The ASI were also mixed, a fusion of a population descended from earlier farmers expanding out of Iran (about 25 percent of their ancestry), and previously established local hunter-gatherers of South Asia (around 75 percent of their ancestry).
So the ASI were not likely to have been the previously established hunter-gatherer population of India, and instead may have been the people responsible for spreading Near Eastern agriculture across South Asia. Based on high correlation of ASI ancestry to Dravidian languages, it seems likely that the formation of the ASI was the process that spread Dravidian languages as well. (pp. 149-150)
The researchers found that the population with the highest percentage of steppe-related ancestry (and consequently the lowest percentage of Iranian farmer ancestry), was not a geographically defined group, but rather a socially defined group—the Brahmin varna (caste) which has traditionally been associated with ritual practices and the interpretation of sacred texts in the Hindu religion. This implied that the Ancestral North Indians contained internal caste divisions of their own prior to encountering the Ancestral South Indians:
A natural explanation for this was that the ANI were not a homogeneous population when they mixed with the ASI, but instead contained socially distinct subgroups with characteristic ratios of steppe to Iranian-related ancestry.
The people who were the custodians of Indo-European language and culture were the ones with relatively more steppe ancestry, and because of the extraordinary strength of the caste system in preserving ancestry and social roles over generations, the ancient substructure in the ANI is evident in some of today's Brahmins even after thousands of years.
This finding presents yet another line of evidence for the steppe hypothesis, showing that not just Indo-European languages, but also Indo-European culture, as reflected in the religion preserved over thousands of years by Brahmin priests, was likely spread by peoples whose ancestors originated in the steppe. (p. 152)
Another relevant finding was that the Ancestral North Indian population contributed far more male DNA to the population of modern India than female DNA as indicated by the Y-chromosome which is inherited exclusively from fathers. Between 20-40 percent of Indian men carry a Y-chromosome that descends from a single male ancestor living between 6800 to 4800 years ago. By contrast, nearly all mitochondrial DNA is native to the Indian subcontinent—even in the north—indicating an origin in the ASI population.
This meant that ANI males were far more successful at leaving offspring that either ANI women or ASI men, suggesting something of a harem effect. A similar trend was found in European DNA from the Yamnaya-derived ancestry.
Today, ANI ancestry in India derives more from males than from females. This pattern is exactly what one would expect from an Indo-European speaking people taking the reins of political and social power after four thousand years ago and mixing with the local peoples in a stratified society, with males from the groups in power having more success in finding mates than those from the disenfranchised groups. (pp. 140)
Researchers also detected significant bottlenecks—sharp reductions in genetic diversity—in a number of modern-day Indian populations. These indicated that after a certain point populations in India no longer mixed freely, but instead reproduced endogamously, meaning only within their socially-defined group (i.e. varna or jati). That is, the genetic evidence verified a deep institutional history for the Indian caste system—a history which must have extended very far back in time based on both the antiquity and persistence of such bottlenecks.
Due to these bottlenecks, genetic diversity in many modern-day Indian populations is greatly reduced leading to an increased susceptibility to a number of genetically-related health conditions. Such conditions are also seen in a number of other ethnic groups who were reproductively isolated from the surrounding population for long periods of time such as Finns and Ashkenazic Jews. The degree to which people married exclusively within their in-group was remarkable, as was the genetic similarity within the various populations. This means that the Indian population today is not homogeneous, even at a genetic level, but can be seen as a multi-ethnic society as diverse as that of Europe but with social (i.e. caste) and linguistic divisions substituting for ethnic and cultural ones.
The genetic data told a clear story. Around a third of Indian groups experienced population bottlenecks as strong or stronger that the ones that occurred among Finns or Ashkenazi Jews...Many of the population bottlenecks in India are exceedingly old. One of the most striking we discovered was in the Vyasa of the southern Indian state of Andhra Pradesh, a middle caste group of approximately five million people whose population bottleneck we could date to between three thousand and two thousand years ago.
The observation of such a strong population bottleneck among the ancestors of the Vyasa was shocking. It meant that after the population bottleneck, the ancestors of the Vyasa had maintained strict endogamy, allowing essentially no genetic mixing into their group for thousands of years. Even an average rate of influx into the Vyasa of as little as 1 percent per generation would have erased the genetic signal of a population bottleneck...And the Vyasa were not unique. A third of groups we analyzed gave similar signals, implying thousands of groups in India like this. Indeed, it is even possible that we were underestimating the fraction of groups in India affected by strong long-term endogamy...
What the data were showing us was that the genetic distinctions among jati groups within India were in many cases real, thanks to the long-standing history of endogamy in the subcontinent.
People tend to think of India, with its more than 1.3 billion people, as having a tremendously large population, and indeed many Indians as well as foreigners see it this way. But genetically, this is an incorrect way to view the situation. The Han Chinese are truly a large population. They have been mixing freely for thousands of years.
In contrast, there are few if any Indian groups that are demographically very large, and the degree of genetic differentiation among Indian jati groups living side-by side in the same village is typically two to three times higher than the genetic differentiation between northern and southern Europeans. The truth is that India is composed of a large number of small populations. (pp. 144-146)
A relevant question for archaeologists is to what extent Iranian farmers contributed genes and culture to the Harappan civilization of the Indus river valley—the earliest known archaeological civilization in the region which flourished between 4500 to 3800 years ago. That civilization ended abruptly, possibly due to natural disasters, invasion, or—most likely—shifts in the monsoon cycles. It’s possible that this culture is the ultimate origin of the Dravidian languages of southern India, but the Indus Valley writing system has yet to be deciphered making it difficult to verify.
Were the inhabitants of this enigmatic ancient civilization Ancestral North Indians, Ancestral South Indians, Iranian farmers, some sort of mixture of these groups, or something else entirely? To date, no genetic material from this culture has so far been analyzed making it a prime subject for future study.
These results reveal a remarkably parallel tale of the prehistories of two similarly sized subcontinents of Eurasia—Europe and India. In both regions, farmers migrating from the core region of the Near East after nine thousand years ago—In Europe from Anatolia, and in India from Iran—brought a transformative new technology, and interbred with the previously-established hunter-gatherer populations to form new mixed groups between nine thousand and four thousand years ago.
Both subcontinents were then also affected by a second later major migration with an origin in the steppe, in which Yamnaya pastoralists speaking an Indo-European language mixed with the previously established farming population they encountered along the way, in Europe forming the peoples associated with the Corded Ware culture, and in India eventually forming the ANI.
These populations of mixed steppe and farmer ancestry then mixed with the previously established farmers of their respective regions, forming the gradients of mixture we see in both subcontinents today. (pp. 151-152)
The Indian population, then, is a mixture of these two populations: Ancestral North Indians (ANI) and Ancestral South Indians (ASI). The ANI are a mixture of Iranian farmers and steppe herders, while the ASI are a mixture of Iranian farmers and indigenous hunter-gatherers. This is reflected in the linguistic and cultural divisions of modern India.
How ancient DNA may rewrite prehistory in India (BBC)
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