Category: Genetics

Readers of this weblog may sometimes notice that I break out in pompous and self-important declarations of being a “scion of the All-Father.” This is basically a joke. But, it’s a joke that draws from a legitimate basis of science and mythology. The “All-Father” is another name for Odin. I’m really talking about Indra, who is probably more like Thor. And obviously, Norse paganism is only distantly related to the mythology of the Indo-Aryans. As someone more familiar with the lineaments of Northern European mythology than Indian, of course, it’s easier for me to draw on the motifs of the former to relate to the latter.

The scientific component has to do with R1a. Specifically, R1a1a, defined by the M17 mutation (discovered by my boss at my day-job 20 years ago). There are two very closely related “clades,” that is, families of pedigrees, of this Y chromosomal lineage, passed from father to son. One of them defines mostly European R1a1a, Eastern Europeans, and to a lesser extent Western Europeans. Another branch is found mostly in Central and South Asia.

When I first saw this distribution around the year 2000 it left me scratching my head. Of course, I knew about the Indo-European languages. But I had always assumed that the demographic impact of the original Indo-Europeans was relatively marginal. And yet this Y chromosome was found at frequencies in the 10-50% range across vast swaths of Eurasia.

Much of the 2000s was spent on arguments as to whether R1a was indigenous to South Asia or to Central Eurasia. Ultimately these arguments were not resolvable due to limitations of the data. To calibrate dates and diversity researchers relied on microsatellites, which are useful due to their high mutation rates, but also erratic for the same reason (not only were confidence intervals wide, some of the assumptions of the model parameters were guesses).

In the early 2010s, whole-genome sequences of Y chromosomes came online. It became very clear that the most common R1a1a lineages exhibited the “star phylogeny.” Demographically, what this means is that men carrying this lineage underwent very rapid population expansion for a short period of time. So rapid that a “father” lineage would give rise to numerous “son” lineages one mutational step away

You can see in the figure that node “A” has given rise to a “star phylogeny.” A large number of individuals are one mutational step away from that genotype. A more normal phylogeny would produce a complex structured tree which accrues mutations across the various branches gradually.

In the South Asian context, a paper from 2004, Independent origins of Indian caste and tribal paternal lineages, introduced a result which prefigured what we now know:

Analyses of molecular variance also suggest that caste groups are more homogeneous for Y chromosome variation than tribal groups, since the variance among caste groups (sampled from all over India) is 3-fold less than that observed among tribal groups and 2-fold less than that observed among all Indian populations grouped together (Table 3). Moreover, if only north caste groups are considered, the variance among populations is not significantly different from zero (Table 3), indicating that spread over the Indian subcontinent although they are located up to ∼1500 km away from each other, these populations have highly homogeneous Y chromosome compositions.

The implications of the lack of structure of R1a on the Indo-Gangetic plain is always something that struck me. It suggested that the paternal lineages only recently expanded since they didn’ have time to build up distinct regional mutations. In contrast, the adivasi populations had a wider distribution of Y chromosomal haplogroups, and they exhibit a lot deeper diverged lineages.

Which brings me to the personal angle. In the spring of 2010, I did my first personal genomic test. I got my Y and mtDNA results back first. It turned out my Y was R1a1a, and my mtDNA was U2b. I was surprised by both. Eastern Bengali has the highest fraction of mtDNA macrohaplogroup M in the world. R1a1a was less surprising. But, it was very strange to have a concrete, personal, connection to this lineage which had been on my mind for a decade or so.

My funny attachment to my haplogroup is probably a function of my upbringing. Growing up as brown in the United States, I wasn’t exposed to Indian culture, nor was I well versed in the details of South Asian communalism. My family is pretty conventional in being upper-middle-class Bengali Muslims, so there is not a jati identity or anything like that I could identify with (and though my parents are Muslim, they are not extremely so, therefore religious identity was a background and not foreground variable). When I looked at my overall genome in 2010 it was clear I didn’t have the “runs of homozygosity” that characterize many people from South Asian backgrounds who come from endogamous communities. I know some of my ancestors were Kayasthas, and my father has some Brahmin ancestry, but the most distinctive thing about me in hindsight is I’m a typical east Bengali with more than a usual dollop of East Asian ancestry (my family is from Comilla).

My Y chromosomal haplogroup, in contrast, is something clear, distinct, and precise. It is an anchor, something which I use to channel my preoccupations and concerns. I don’t have Omar’s Gujar tribal ancestry, or Zach’s Muhajir/Persian origins. I’m just a brown American whose parents did not instill him a patriotism about the “motherland” (Bangladesh), because they themselves didn’t even live a decade in that nation. Though there is a spectrum, it is clear that many South Asian Americans are less “coconut” than I am, and are attuned to fine differences of status, origin, and background. Growing up around only white people my identity was racialized, not ethnicized.

I have never felt superior or inferior to any community or ethnicity of South Asian because I never belonged to any community, have weak ethnic identity, and don’t believe in any religion. The religious prejudices I do have are probably Anglo-Protestant ones against Catholicism, because of the implicit assumptions and background facts of America’s Whig culture.

What R1a1a symbolizes to me is that I have a concrete connection to a semi-historical phenomenon between the end of prehistory and before the written word, which we have not grasped or understood very well. Though it is true R1a1a is found at higher concentrations in “upper castes,” as well as in the north and west of the subcontinent, and among Indo-Aryan speakers, the reality is it is found in almost every community in South Asia (the main exception being among Tibeto-Burmans and Munda). There are many communities, such as Chenchus, which have very little steppe ancestry but retain a substantial proportion of R1a1a.

For obvious reasons this haplogroup is associated with Indo-Aryans (the earliest find of R1a1a-Z93 is from the Bronze Age Volga Srubna culture), but its reach is far beyond current areas of Indo-Aryan speech. Its ubiquity is a testament to a broader South Asia cultural matrix that emerged in the centuries after 1500 BC, from north to south.

This is of course not a moral judgment. The expansion of this paternal lineage at the expense of others likely occurred through a process of aggression and social exclusion. This is nothing to be proud of…or ashamed of. It’s just a description.