Wednesday, June 6, 2018

Neolithic bottleneck of Y-chromosome had its epicentre in India since Yayati’s times.

A recently published paper by Zeng et al of the Stanford University proposes socio-cultural causes for the sudden and simultaneous appearance of a ‘bottleneck’ in Y-chromosome diversity across the Old world (Asia, Europe and Africa) around 5000 -7000 BP. The two limits of this date correspond to eventful India of those times with the lower date coinciding with the traditional date of Mahabharata and the upper with Ramayana period extending upto Yayati’s times whose descendants spread out to Europe. The authors’ postulation of socio-cultural causes for this bottleneck further reiterates the suitability of the events in India of those times in giving rise to a bottleneck in male lineage across the world and more intensely in Eurasia.

The paper by Zeng et al is an improvisation or development over a previous paper published in 2015 by Karmin et al of Arizona University. The extent of the bottleneck proposed by Karmin et al was 4000 -8000 BP which is also very much within the span of momentous events in India. A sudden drop in genetic diversity of male centric Y-chromosome had happened in this period while the female centric mtDNA had continued to thrive without any reduction. The authors did not see the reduction in Y chromosome diversity as a case of biological survival of the fittest, but of a “reproductive success of a “limited number of ‘socially fit’ males and their sons” caused by “the accumulation of wealth and power”

Using the same data, Zeng et al hypothesized the effect of repeated wars over generations in wiping out many male lineages while losing considerably the males of their own clan thereby leading to a drop in male genetic diversity. The tricky part is that there was a sudden and sharp drop in genetic diversity of male chromosome but not in the overall size of the male population. There is no such change in female diversity and population-size. These made them fine tune their hypothesis by comparing the patrilineal and non-patrilineal groups. Their models showed acute loss of diversity in patrilineal groups - in the lineages from a common ancestor - to the extent that there was just one male for 17 women.

According to them a common cultural ethos promoted high levels of Y-chromosomal homogeneity from a common descent and also ‘high levels of between-group variation’. The presence of many groups of common patrilineal descent also resulted in inter-group competition, leading to clashes that wiped out lineages, which is genetically perceived as a drop in genetic diversity. Their computer simulations of patrilineal societies showed early extinction of many haplogroups in the beginning with one or many other haplogroups quickly becoming dominant in frequency. The same is not found in non-patrilineal societies where very less number of haplogroups became extinct and overall representation continued till the end of simulation. 

The inference from a layman point of view is that different groups that sprang from a common ancestor did undergo a politico-military survival of the fittest for a couple of millennia between 5000 -7000 BP (or 4000 -8000 BP as per Karmin et al) and ended up with specific groups among them becoming dominant and continuing the progeny. The surprising element is the simultaneity of this phenomenon across the Old World.

The Old World covered by Karmin et al was Africa, the Andes, South Asia, near East and Central Asia, Europe and Oceania. The DNA samples were taken from 456 males from these regions for the study. Following illustration shows the sampling locations.

The dominant feature of this map is non-representation of China in the study. It is difficult not to think that the sampling pattern of Eurasia follows the popular conception of western academia of PIE or IE or Aryan migration from central Europe to India (South Asia), leaving out China. The socio-cultural hypothesis of this study is presumed to be largely influenced by the western perception of PIE.  

Another feature that catches up attention is why neither of the teams left untouched the most striking feature, namely the surprising simultaneity of the bottleneck in all these regions across the globe. Though the bottleneck lifts are connected with the rise of regional polities and statehood in the respective regions, what caused the bottleneck around the same time in all the seven regions of the five continents leaves very less to speculate.  Was there a singular force having a global reach?   
To answer this, let us take a look at the bottleneck curves for all these regions.  They tell a story of their own which Zend et al did not probe.  

In the above map the red curve represents mtDNa and yellow curve, Y-chromosome. The sudden dip in the yellow curve (Y-chromosome) in all the regions in the period 5000-7000 BP (or 4000 -8000 BP), except Siberia and Andes is striking. The bottleneck is less extreme in South East and East Asia whereas it is more in Near East and Europe. But Zeng et al clubs together West Asia, Europe and South Asia in their paper as having similar trend which is not true as per this figure.
South Asia (India) presents a unique shape of a winnowing basket or a flat bottomed bowl and not a sharp curve as with Europe and Near East. This covers a longer time period than it is for other regions. The figure shows that the drop in male genetic diversity had started soon after 10,000 BP.

One can see the yellow curve gradually dropping down even since 10,000 BP and flattening a couple of millennia later. The lift comes approximately another 4000 years later. That is, for a period of roughly 6000 years since the beginning of 10,000 BP the male genetic diversity had been much less. Applying the rationale of Zeng et al, this period had seen a severe and continuing power struggle within the same patrilineal clan.

Such prolonged dip is found only in India and not in any other regions under study. In other regions the bottleneck is found simultaneously in the period 5000 -7000 BP which falls well within the flat bottom period of India between 4000-10,000 BP.

Only other exception is Central Asia which however has been explained by Zeng et al.

They say,

“Central Asian pastoralists, who are organized into patriclans, have high levels of intergroup competition and demonstrate ethnolinguistic and population-genetic turnover down into the historical period. They also have a markedly lower diversity in Y-chromosomal lineages than nearby agriculturalists. In fact, Central Asians are the only population whose male effective population size has not recovered from the post-Neolithic bottleneck; it remains disproportionately reduced, compared to female estimates using mtDNA. Central Asians are also the only population to have star-shaped expansions of Y-chromosomes within the historical period, which may be due to competitive processes that led to the disproportionate political success of certain patrilineal clans.”

The above figure is self-descriptive of a power struggle or unrest in Central Asia with a continuing lower diversity of male lineages for thousands of years. However the sudden dip has happened in 5000-7000 BP in tune with other regions.

A glaring feature in this scenario is that South Asia is in the centre of the all the regions that experienced the bottleneck simultaneously. And South Asia experiencing the bottleneck for a much extended period within which the bottlenecks occurred in the surrounding regions makes it plausible that South Asia was the epicentre of the struggle that resulted in dispersal to the neighbouring regions. The power struggle among the dispersed clan in the newly settled regions had caused the sudden dip in the male diversity between 5000 -7000 BP.  

Even though Southeast and East Asia enjoyed a steady and higher coalescence between female and male lineages, the bottleneck did appear in the same period as in Europe but less intensely. For Europe, Central Asia and South Asia, the authors echo the same sentiment as PIE proponents of a distribution of pastoral culture. But the large flat bottom of South Asia does not correspond to the pastorals coming from Europe and causing bottleneck in India in the power struggle. Contrary to that the figure suggests a long history of sibling rivalry in India ever since 10,000 BP and a spill over to Europe and central Asia. The history of Bharat known from Itihasas and Puranas also establish this spill over due to power struggle among same patrilineal clans.

The most well known spill over was that of Yayati clan. Even Ramayana accounts for the spread of the kins to distant lands to establish independent suzerainty. By Mahabharata times struggle for power has become a regular norm with numerous clans of west Asia and Europe siding with the two sides that belonged to the same Kuru clan. One can say that Mahabharata war was a high point of a clash of patrilineal clans that caused a severe bottleneck in the male progeny. Needless to say that the revival from bottleneck coincided with post Mahabharata period, in 4000- 5000 BP.

Historical evidence from India on patrilineal group struggle.

Sibling rivalry is inherent in human nature. Having understood the extent of damage it could do to a family, the early ancestors of Bharat had favoured migration to distant lands and setting up polity by conquering those regions. For a long time since Manu, transfer of power was to the eldest son only. The Ikśvāku-s followed that tradition (VR 2-110-35). The younger siblings had to see newer pastures.
Rama himself says this in justifying his acceptance of Vibhishana. Kin of the same family do not see eye to eye. (VR 6.18.10 and 14)

“It is told that persons of the same family and rulers belonging to adjoining territories become enemies and strike in times of adversities. For this reason, he (Vibhishana) came here.”

 “Kinsfolk do not live together in a fearless mode and in a delightful manner. Hence, they get a split among themselves.”

Rama envisions a personal enmity between the brothers, Vibhishana and Ravana and justifies that it is common to see this – a perfect example of the patrilineal enmity that Zeng et al proposes to explain the genetic bottleneck.

The enmity and rivalry forced the siblings to go to distant places to set up their own kingdoms and start dynasties in their name.  The Chola dynasty was one such off-shoot of the Solar dynasty that traced its beginnings to Ikśvāku.  The presence of many branches of lineages and the mix-up of names of ancestors in the chronology given by Puranas can be attributed to this.

The first ever migration of siblings was that of Amāvasu, whom the western Indologists see as a migrant Aryan. Amāvasu was one among six children born to Pururavas and Ila, the daughter of Manu. The eldest was Āyus who became the inheritor of the throne (VR 4.7, MB 1.75). The kingdom was his and there was no need for him to look for newer pastures. This is also ascertained from the name Āyu – that has many meanings, among which ‘descendant’ or ‘offspring’ are suitable for him as the eldest son. On the other hand, Amā in Amāvasu means ‘in the house of’ or ‘non-authority’, indicating a co-existence with his eldest brother.  

A verse in Baudhāyana Śrautasūtra  suggests that Amāvasu went to the West in the regions of Gāndhāra, Parśu and Arāṭṭa. Further movement to West Asia and Europe was well within reach of those who left home. Sage Vishwamitra was the 11th descendant of Amāvasu and he preferred to stay in Bharat.

Yayati clan.

Another important patrilineal clan that dispersed out of India comes from the house of Yayati. This family has all features of a mix of European and Indian races. One of the wives of Yayati was of Danu’s lineage. Of the three sons born to her two went out of India due to sibling fights while one stayed back in India and continued the progeny that can be detected as a strong European mtDNA mix-up in Indian population.

Of the two who went out of present-day boundaries of India, Anu went to the West and Druhyu to North and North West (central Europe). They would not have gone alone but accompanied with their well wishing kin. Conquests of new regions could have happened in the following period causing considerable extinction of native lineages.

While on the West this march was going on, an expedition was launched on East Asia too. Puru, the other sibling of Anu and Druhyu who stayed back in India had a son named Janamejaya. The son born to Janamejaya went to the countries to the east of India till the region where the sun rises – a reference to Udayagiri in Fiji Islands. Ramayana also describes the route till Udaya Parvata (VR 4.40. 54, 55) indicating the familiarity with the regions of the east and frequent travels to them.

The son of Janamejaya and grandson of Puru was perhaps inspired by the western occupation of Puru’s siblings and tried his hand in conquering eastern part of the globe. It is for the reason that he brought eastern countries under his power, he was called as “Prachinvat” (MB 1-95).

Thus we have two records in ancient history of Bharat of the same paltrolineal clans making inroads in West and East of India. Those who went to West ended up in power struggle later that finally reflected in genetic bottleneck. Such violent reflections were less in the eastern sector. But the simultaneity of the bottleneck in the west and east of India has the backing of history of India in Anu and Druhyu in the west and Prachinvat in the east.

Rama was born 20 generations after Anu as per the genealogy given in Vishnu Purana 4-18. Rama was not genetically connected with Anu but his father’ friend Romapada was the 20th descendant of Anu. Assuming 3 generations for a century, Rama can be presumed to have been born 700 years after Yayati.

The flat bottom of the bottleneck coincides with Rama’s period (7000 BP as per Pushkar Bhatnagar’s decipherment of Ramayana and the corresponding date of sage Agastya, a contemporary of Rama, which is known from the sighting of star Agastya to the north of Vindhyas for the first time ). Though Rama was wary of sibling rivalry of other dynasties, he didn’t experience the same in his family. But all his brothers and brothers’ sons set up kingdoms in far off regions with Bharat’s sons reaching to North West India.  

Rama’s reign was felt far and wide – in west Asia too, known from the fact that many cities of West Asia and Middle East had their name connected to Rama. The relative calm in rivalry for the next millennium perhaps ensured a horizontal progression of the genetic curve. This ended by Mahabharata times, which saw extermination of own lineages and other lineages as well. By the end of Mahabharata war the territorial rights were more or less established and this is made out from lifts from bottlenecks.

An expansion of each of the above mentioned historic events will stretch further this monograph. But what is to be made out is that India had a prolonged history of struggle for power among the clans of a common ancestor. The loss of males in wars and occasional loss of complete lineages is more palpable in the research study matching with history. This is bound to have a profound impact on dismantling the Aryan Invasion ideas.

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