A Discussion on genetic deciphering to understand human migration
I have been getting into this subject and out of it so many times, so I finally decided to put down what I gleaned and be done with it, till more definitive answers were available. It was indeed a complicated subject and one which was very subjective. As you may have noticed it started with comments that one can get to our roots easily by studying the genetic makeup and divide it by castes and tribes. Easier said and done and that I agree with after so many forays into the subject. Ethiran kathiravan an eminent blogger and one who like me, loves movies and music had previously written a great article on this subject. I will refer to it often and augment it with inputs from a few other books, papers and a text book my ‘medical student’ son gifted me in exasperation (did not want me to come up with half-baked theories, as he said)after some arguments on migration.
Anthropology is an exacting study exemplified by eminent persons like the late LA Anathakrishna Iyer of Palghat, one of the first to venture into it. However, nowadays the methods have drifted more towards genetic studies and involve microscopes and computers. That such studies provide much insight to migration is amply clear and the methods used are quite interesting. Let us first see what is done from a very superficial level, and please note here that I am neither an expert nor a recurring student of this topic, but just somebody who tried to glean through some of these studies with interest.
Armed with all that I got into a brief study of what they term Proto Dravidians, in an area where much mingling of people occurred, both aborigines, invaders as well as visitors, to create thirty four or so groups. When a man belonging to one such group bonds with a girl of another, the resulting offspring carried properties of both. As time goes by and as generations of people are created by the offspring of this union the genetic sequence that one studies, exhibits what one could term a secret diary of the years and what happened. A genetic Sherlock Holmes puts meat into the study and comes up with startling results by unraveling the gene sequences and structure. How would that be possible? Well, as we note, a child carries chromosomes from both parents in a standard genetic structure or sequence. But then again, there are slight variations and these are called polymorphisms which can sometimes be observed over a wider population.
If parents have differing polymorphisms, the child carries both (John Tainer explains scientifically - For genetics, a polymorphism refers to genetic variants within the population that allow evolution by natural selection. A mutation may create a polymorphism in the population if the resulting variant form is transmitted to subsequent generations without causing major defects in biological functions). There is one other term one has to understand to get going and that is a term called Allele. An allele is defined an alternative form of a gene (one member of a pair) which is located at a certain position on a chromosome. This kind of genetic coding determines very distinct traits which are passed on from parents to their children. Gregor Mendel was the first to study this and formulated what is known as the Mendel's law of segregation (It is also to be noted here that organisms have two alleles defining each trait). Typically alleles of a heterozygous pair have one which is dominant and another, recessive. A study of distinct alleles can help one study migration or events in a specified population over time. These are the signatures or unique codes which a genetic detective studies to get to the point of singular origin.
Perhaps this is all quite confusing to the lay person, so a paragraph on the fundamentals would be useful. As we all know our body comprises zillions of cells. Some cells are somatic which compose the body structure and others are gamate or reproductive i.e. comprising of sperms or eggs. Every cell has 23 chromosome pairs (a genome) and each of these chromosome pairs have some 25,000 genes. The nucleus of a somatic cell thus comprises of 46 chromosomes, 23 from each parent whereas the gamate comprises only 23. Of the 23 pairs, 22 are termed autosomes and one sex chromosome. Alternative versions of genes account for variations and are based on inherited characteristics - termed alleles. Getting a little deeper, each gene comprises four different arrangement of atoms called bases or nucleotides. These are termed as G, A, T & C, each being a unique arrangement. So when one goes on to decipher a genome, he ends up writing a very long sequence using these 4 alphabets (In addition to the 25000 or so of these genes, there is also a lot of junk DNA).To summarize, genes are made of DNA, a genome is made up of genes and the genome has some 3 million bases or bits of information in them. This field is quite interesting and produces many pointers to where we are headed. As some of you may be aware, males have an X and a Y chromosome and females have 2 X chromosomes. The Y chromosome is gene poor and deteriorating, so will be gone in another 125,000 years, so you never know, males may become extinct!!!
And so looking back into our own history thus far, you will realize that it becomes a story of the wandering Y. But well, a study of alleles (certain specific ones like the HLA or Human leucocyte antigen) and their distribution frequency over a certain area can establish certain conclusions. In general this kind of study is a study of haplotypes. Put in simple words, haplotype is the group of genes that a progeny inherits from one parent. As time goes by you will see many more of these statistical studies to determine community migration paths and family history, triggered by for example Nairs who want to determine their ancestry, Ezhavas who want to determine theirs, each caste tired of the old myths and legends which talk about gods and kings having determined their fate.
Reference paper 1: One of the first analyses were tabulated in reference paper by Thomas, Nair and Banerjee in 2006. This analysis of HLA-A & C alleles in Pulayas, Nambuthiris, Malabar Muslims, Syrian Christians, Ezhavas and Nairs was conducted using a number of genetic samples. Some very general conclusions on genetic drifts were arrived at by these experts after comparing the HLA alleles. They were
- The tribal Dravidians of Kerala stood somewhat pure and isolated compared to a veritable mix in N India. The Pulaya and Kurichiyars seem to the original aborigines or ancestral stock.
- Malabar Muslims and Syrian Christians, based on the B35 and CW04 alleles show a characteristic Mediterranean influence showing a migratory pattern more consistent with history.
- Nairs show an influence of the European B07 and CW07 more often seen in Belgium Germany and Scottish populations. They also have the highest mix of alleles and corroborate North Indian influence, with connections to the Newars of Nepal.
- Ezhavas and Nambuthiri’s also exhibited influence from European as well as central and East Asian genetic pools.
- The Ezhava shows an eastern and Mongoloid influence, signifying a possible Buddhist past.
Reference paper 3: Now we look at a third study by the same group, this one focused on the 17 YSTR marker over 168 males which showed a peculiar connection to the males of Vasterbotten in Sweden as well as East Asian (Taiwan, China, Thailand) countries. Some connections were also seen to Afridi’s, Pathan’s and so on.
Reference paper 8: Ethiran Kathiravan also dwelt on some of these studies and agrees that no definitive pattern could be identified while it becomes clear that Pulayas and other hill tribes were the original aborigines of Kerala whereas all other non-Dravidian groups had much of intermixing, with significant contributions from other wanderers.
Reference paper 9: Andrew J Bohonak, San Diego State University, San Diego, California, USA states provides an interesting explanation - Genetic drift consists of changes in allele frequencies due to sampling error. Even if all individuals in a population have the same opportunities to mate, their reproductive contributions to the next generation will vary due to random chance alone. In any population of finite size, this sampling error will cause gene frequencies to fluctuate from generation to generation. Genetic changes due to drift are neither directional nor predictable in any deterministic way. Nonetheless, genetic drift leads to evolutionary change even in the absence of mutation, natural selection or gene flow.
Reference paper 4: While all this was going on, a team of Indian scientists got working on the popular folktale related to Parayi Petta panthirukalam (we will get to it another day - for a detailed account read Dr Rajan Chungath’s book or the Aithihyamala). Ethiran Kathiravan also focuses on this tale and its impact. But for those who do not know, there is an ancient legend in Kerala titled ‘Parayi petta panthirukulam’ and deals with the twelve offspring of a low caste woman and their lineage. As the story goes, Vararuchi, one of the nine wise men in Emperor Chandragupta Vikramaditya’s (375 – 415 AD) court married a Paraya girl (an orphan who came with the raging waters of Bharatapuzha and was raised at the Naripatta mana). As he married a lower caste woman, he excommunicated himself and the couple then set out on a long trip or pilgrimage in the course of which they were blessed with 12 children – 11 boys and a girl. As each child was born, Varuchi would enquire if the child had a mouth and if the answer was in the affirmative, Varuchi would say ‘good, God will take care of him’ and they would abandon him on the way. Each of these children ended up being cared by families of various castes, high, medium or low. It is said that the families which adopted these children were Mezhathol Agnihothri (Brahmin), Pakkanar (Parayan), Rajakan (Dhobi), Naranathu Bhranthan (Elayathu), Karakkal Matha (Nair adopting the girl child), Akavoor Chathan (Vaishya), Vaduthala Nair (Nair), Vallon (Pulaya), Uppukuttan (Moplah), Pananar (Panan, country musician) and Perunthachan (Carpenter). Interestingly the last and 12th child was born without a mouth. Vararuchi sadly buried this child near a hill. This location is supposedly near Kadampazhipuram in Palakkad and known as “Vaayillaakkunnilappan” (Hill Lord without mouth).
The descendants of these children live at Shornur, Pattambi and Thrithala of Palakkad district of Kerala state and despite the differences in their caste and social status, these families are bound together by various rituals and religious customs. These were the subjects of the next study, but when the group headed by Suresh collected genetic samples from these families to study the patterns, they actually found that the results were contrary to the folktale and common haplotypes were not detected across the tested families with the result that co-ancestry could not be proven.
Why mention this? Well it is to prove that genetic sampling and studies are not always conclusive when you span many generations and so hype about genetic studies is not a good thing. The authors concluded thus - Considering that the survival of a lineage from a single founder through 20 generations (approximately 700 years) is only 9.6%, the chance of survival of Vararuchi’s lineage, which is believed to have originated 1600 years ago (45 generations) is meagre. On the other hand, it is also possible that the haplogroups of different families, who adopted Vararuchi’s children, were different and had multiple own men at the time of adoption. The true descendants of Vararuchi’s sons may have been either extinct through time due to different genetical or social reasons or severely declined in relation to the descendants of the own men of a family lineage. Alternatively, the Vararuchi episode may be a pure myth.
Reference paper 5: In the next paper covering directional migration, we come across another interesting conclusion - Migrants leaving the high status castes showed a greater probability of entering the middle-status castes than entering the low-status castes. Migrants leaving the middle-status castes showed a greater probability of entering the low-status castes than the high-status castes. Why so? The Hindu concept of anuloma, for instance, occasionally permits men to marry women of lower caste, while women are rarely permitted to marry men of lower caste. This mechanism of movement implies that females should be more “upwardly mobile” than males, and it has been suggested that anuloma is the source of greater female inter-caste mixing inferred from genetic data.
Reference paper 6: The next paper on genetic affinities covers a wider study and concludes that - No significant difference was observed in the mitochondrial DNA between Indian tribal and caste populations, except for the presence of a higher frequency of west Eurasian-specific haplogroups in the higher castes, mostly in the north western part of India. On the other hand, the study of the Indian Y lineages revealed distinct distribution patterns among caste and tribal populations. The paternal lineages of Indian lower castes showed significantly closer affinity to the tribal populations than to the upper castes. The frequencies of deep-rooted Y haplogroups compared to the upper castes. However, Y-SNP data provides compelling genetic evidence for a tribal origin of the lower caste populations in the subcontinent. Lower caste groups might have originated with the hierarchical divisions that arose within the tribal groups with the spread of Neolithic agriculturalists, much earlier than the arrival of Aryan speakers. The Indo-Europeans established themselves as upper castes among this already developed caste-like class structure within the tribes.
Reference paper 7: But one has to look at the Tamil areas to compare conclusions. So we look at yet another study where the conclusion is that Genetic data from Y-chromosome, mtDNA, and autosomal STRs are in accord with historical accounts of northwest to southeast population movements in India. The influence of ancient and historical population movements and caste social structure can be detected.
Times Of India article: But CCMB scientist Kumarasamy Thangarajan states - There is no truth to the Aryan-Dravidian theory as they came hundreds or thousands of years after the ancestral north and South Indians had settled in India. The genetics proves that castes grew directly out of tribe-like organizations during the formation of the Indian society. The study provides an interesting conclusion
Between 135,000 and 75,000 years ago, the East-African droughts shrunk the water volume of the Lake Malawi by at least 95%, causing migration out of Africa. ``The initial settlement took place 65,000 years ago in the Andamans and in ancient south India around the same time, which led to population growth in this part,'' said Thangarajan. He added, ``At a later stage, 40,000 years ago, the ancient north Indians emerged which in turn led to rise in numbers here. But at some point of time, the ancient north and the ancient south mixed, giving birth to a different set of population. And that is the population which exists now and there is a genetic relationship between the population within India.''
Reference paper 11: And the last paper emphasizes European connections - Our results show the presence of west-Eurasian typical mtDNA haplogroups in Indian tribes, presumably resulting from admixture with Indo-Europeans (i.e. who probably introduced the caste system in India). This interpretation would suggest that caste people initially possessed west-Eurasian mtDNAs rather than Asian mtDNAs. This view is reinforced by the fact that caste groups are more similar to west Eurasians than are the tribals .In summary, although the data support a recent India–Australia connection, we could not find in Indian tribals any unquestionable genetic signature of the approx. 60 000 year-old migration from Africa to Sahul following the postulated southern route. A possible explanation would be that such migration never occurred along that route. Alternatively, the early migrants from Africa may have made their way to Sahul following the southern route without settling in India. Another possibility, which is probably the most reasonable one, is that in India the genetic traces of early migrations along the southern route were erased by the subsequent migrations which shaped the present-day mtDNA gene pool of India
Reference paper 8: This is all in line with Ethiran Kathiravan’s conclusions that you will find connections to lower caste tribes even in the progeny of the highest classes and there is always certain amount of intermixing in populations. So the notion of purity in races and classes or castes is a bigger myth.
But then again to detect migratory patterns, the study of genetics will help, only that you need access to a large amount of samples coupled with well-funded and dedicated research using proper tools. Presently it is sporadic, based on small amounts of samples and hardly conclusive.
While my own reading of all this was very stimulating, the potential for misunderstanding (If I have already done that please forgive me, for all I wanted to do was make some general summaries on the subject to show its general complexity, but also explaining the general methods adopted) was too much considering my relative lack of in-depth knowledge in the subject. So let us wait and watch as we leave the leg work to the experts….
- A crypto-Dravidian origin for the non tribal communities of South India based on human leukocyte antigen class I diversity R. Thomas, S. B. Nair & M. Banerjee
- Haplotype analysis of the polymorphic 17 YSTR markers in Kerala nontribal populations - Seema Nair Parvathy, Aswathy Geetha, Chippy Jagannath
- Y-short tandem repeat haplotype and paternal lineage of the Ezhava population of Kerala, South India- Seema Nair, Parvathy, Aswathy Geetha, Chippy Jagannath
- Co-Inheritance of Y-Chromosome Haplogroups And Lineages In ‘Parayi Petta Panthirukulam’: An Evaluation Of Human Motifs In A Popular Folktale In Kerala, India. Kumar U Suresh, R. V. Ratheesh, Rajan Chungath, George Thomas, George Sanil
- Directional migration in the Hindu castes: inferences from mitochondrial, autosomal and Y-chromosomal data - Stephen Wooding, Christopher Ostler, B. V. Ravi Prasad, W. Scott Watkins, Sandy Sung, Mike Bamshad, Lynn B. Jorde
- Genetic affinities among the lower castes and tribal groups of India: inference from Y chromosome and mitochondrial DNA Ismail Thanseem1, Kumarasamy Thangaraj, Gyaneshwer Chaubey, Vijay Kumar Singh, Lakkakula VKS Bhaskar, B Mohan Reddy, Alla G Reddy and Lalji Singh
- Genetic variation in South Indian castes: evidence from Y-chromosome, mitochondrial, and autosomal polymorphisms WS Watkins, R Thara, BJ Mowry, Y Zhang, DJ Witherspoon, W Tolpinrud, MJ Bamshad, S Tirupati, R Padmavati, H Smith, D Nancarrow, C Filippich and LB Jorde
- Kerala Kaumudi – Ethiran Kathiravan – Pulayar – The great grandfathers of Namboothiris, Christians and Muslims
- Genetic Drift in Human Populations Andrew J Bohonak,
- Reconstructing Indian population history David Reich, Kumarasamy Thangaraj, Nick Patterson, Alkes L. Price & Lalji Singh
- Mitochondrial DNA analysis reveals diverse histories of tribal populations from India - Richard Cordaux, Nilmani Saha, Gillian R Bentley, Robert Aunger, S M Sirajuddin and Mark Stoneking
Panthirukulathinte Pingamikal – Dr Rajan Chungath
Human Origins – Rob Desalle & Ian Tattersall
The Journey of Man – Spencer WellsDeep Ancestry – Spencer Wells