Genetics and Archaeogenetics of South Asia: Encyclopedia II - Genetics and Archaeogenetics of South Asia - Y chromosome

Genetics and Archaeogenetics of South Asia - Y chromosome

Some researchers (Kivisild et al. 2003b; Cordeaux et al. 2003) emphasize that the combined results from mtDNA, Y-chromosome and autosomal markers suggest that "Indian tribal and caste populations derive largely from the same genetic heritage of Pleistocene southern and western Asians and have received limited gene flow from external regions since the Holocene" (Kivisild 2003b; Cordeaux et al. 2003). However, in 2004 paper Cordaux [5] argues independent origins of Indian caste and tribal paternal lineages: “Thus, the quantitative comparison of an extensive dataset of Y chromosome haplogroups in both Indian caste and tribal groups, as well as nongenetic information, support a scenario of independent origins of Indian caste and tribal paternal lineages, with recent immigration of caste Y lineages and subsequent bidirectional gene flow between caste and tribal groups. This conclusion contrasts with the earlier suggestion that both Indian caste and tribal Y chromosomes largely derive from the same Pleistocene genetic heritage, with only limited recent gene flow from external sources. In contrast with the Y chromosome evidence, the mtDNA evidence suggests a common origin of tribal and caste groups. It is likely that most maternal lineages largely represent the original mtDNA gene pool of India, implying that caste maternal lineages mainly derive from local tribal ancestors.”

The haplogroup R1a1 (M17) has been previously linked with the ancient Kurgan (Yamna - "ямная") culture and Proto Indo-Europeans of Southern Russia/Ukraine, who supposedly migrated to Europe, Central Asia and India between 3000 and 1000 BC (Passarino et al. 2001; Quintana-Murci et al. 2001; Wells et al. 2001). However, the high frequency of R1a1 found in Punjab and in the South Indian Chenchu tribe, together with a higher R1a1-associated STR diversity in India and Iran compared with Europe and Central Asia, indicates that R1 and R1a1 differentiation may have originated in Southern or Western Asia (Kivisild 2003b). The defining M17 mutation has also been found in several South Indian tribes (Kivisild 2003b; Ramana et al. 2001; Wells et al. 2001). Stephen Oppenheimer, who reports upon the results of the Human Genome Diversity Project in his book "The Real Eve: Modern Man's Journey out of Africa", comments that, "For me and for Toomas Kivisild, South Asia is logically the ultimate origin of M17 and his ancestors ... thus undermining any theory of M17 as a marker of a 'male Aryan Invasion of India'" (p. 152). Oppenheimer further believes that it is highly suggestive that India is the birthplace of the Eurasian mtDNA haplogroups which he calls the Eurasian Eves. According to Oppenheimer it is highly probable that nearly all human maternal lineages in Europe (and similarly in East Asia) descended from only four mtDNA lines that originated in South Asia 50,000-10,000 years ago.

Unfortunately, there is not enough data to make the final conclusion about the R1a1 origin. In order to do so, comparative study of R1a1 haplogroup diversity in Ukraine (and/or South/Central Russia), Pakistan and India populations (using the same (large) set of microsatellite markers) is necessary. So far, only one attempt of such study has been made by Passarino in 2001 [6]. This study employs the 49a,f/TaqI Y specific system and the set of seven microsatellite markers to compare diversity of R1a1 (M17, Eu19) haplogroup in 29 world populations (including Ukraine, Poland, and India). According to Passarino (2001) “the 49a,f Ht 11 displays a major diversification in East Europe with respect to the other areas. Actually, in East Europe, all the derivatives of the 49a,f Ht 11 were observed (9 vs 6 in the "Balkans," 4 in the "Middle East," 1 in India, and 2 in West Europe). Moreover, Ukraine presents at least twice as many derivatives as the other East European populations. These findings suggest that East Europe is the place where this lineage originated or started to expand, particularly in Ukraine, which also includes a refuge area during the LGM.” However, more extensive studies, including Pakistan populations (i.e Kashmiri) are necessary to make the reliable conclusions.

Kivisild in his 2003 paper [7] compares diversity of R1a1 (M17) haplogroup in Indian, Pakistan, Iran, Central Asia, Czech and Estonian populations. This study shows, that diversity of R1a1 in India (Pakistan, Iran) is higher, than in Czechs and Estonians. However, one should take into consideration, that the territory of modern Estonia was repopulated after the end of LGM by the small groups of settlers (founder effects are inevitable), not all of whom came from Ukrainian refuge. More than 1/3 of Y chromosome gene pool in Estonians is represented by “Uralic” N3 haplotype [8]. Even Estonian language is not Indo-European. According to Novelletto et al. work, presented on "European Human Genetics Conference 2005", R1a haplogroup was introduced into the Czech population relatively recently (which would guarantee the relatively low diversity), reflecting historical or recent prehistorical events, not the post-LGM re-colonization of Europe. Thus Czechs and Estonians are very poor choice, if one wants to study diversity of certain haplogroup in direct descendants of Paleolithic population of Ukrainian LGM refuge (one of the possible origin places of M17 marker). Ukrainian/South Russian (and m.b. Polish) population most likely would show much greater diversity of R1a chromosomes, than any other European population (see: Passarino in 2001 [9]). However at this point such study is remained to be done. Some new data on R1a (defining mutation of R1a is SRY-1523 = SRY10831, preceding the M17 mutation which defines R1a1) diversity in Southeastern Europe (Croatia, Bosnia and Herzegovina, Serbia and Montenegro, and Macedonia) are represented in 2005 paper by Peričić et al [10]. According to this paper, R1a haplotype shows high diversity in this area (especially in Bosnia and Herzegovina), “and the estimated range expansion at 15.8 ± 2.1 KYA, consistent with its deep Paleolithic time depth”.

The neolithic spread of farmers to Europe from Levant/Middle East has also been linked to 12f2 (haplogroup J) and the markers M35 (haplogroup E3b) and M201 (haplogroup G). But while M35 (E3b) is present in Europe, Anatolia, South Caucasus and Iran, Indians generally do not have the Alu insertion in their Y chromosomes. The lack of YAP+ chromosomes (haplogroup E) in India suggests that M35 appeared in the Middle East only after a migration from Iran to India had taken place, but earlier than the later migration of Near and Middle Eastern farmers to Europe (Kivisild 2003a).

Virtually all modern Central Asian Y-chromosome M lineages seem to belong to the Eastern Eurasian (Mongolian) rather than the Indian subtypes of haplogroup M, which indicates that no large-scale migration from the present Turkish-speaking populations of Central Asia to India (and vice versa) could have occurred (Kivisild 2000). However, one should take in consideration that genetic makeup of the modern Central Asian populations most likely differs dramatically from the ancient population. Ancient mtDNA data [11] indicate the total absence of Eastern Eurasian (Chinese/Mongolian) mtDNA lineages among ancient Kazakhstan samples dated before seven century BC. It is also possible that Y-chromosomal diversity in ancient Central Asia mirrored this noticeably European (“non Middle Eastern”) ancient mtDNA diversity (and all ancient Central Asians had predominantly European ancestry). Unfortunately, no data on ancient Y-chromosomal makeup in Central Asia available so far. The most possible source of these clearly European (“non Middle Eastern”) mtDNA lineages in ancient Central Asia (before 700 BC) is the population of former Ukrainian LGM refuge. If ancient Central Asian population was the source of subsequent Proto Indo-European migration, than this proposed migration into the territory of modern Pakistan apparently happened before the arrival of eastern Eurasian lineages on the territory of Central Asia (before 700 BC).

A 2001 examination of male Y-DNA by Indian and American scientists indicated that higher castes are genetically closer to Western Eurasians than are individuals from lower castes, whose genetic profiles are similar to other Asians. According to Bamshad et al. (2001), higher caste Telugus have a higher frequency of haplogroup 3 (R1a1) than lower castes. Haplogroup 3 is also characteristic for the Eastern Europeans. In the study, Bamshad and his team wrote, "Our results demonstrate that for biparentally inherited autosomal markers, genetic distances between upper, middle, and lower castes are significantly correlated with rank; upper castes are more similar to Europeans than to Asians; and upper castes are significantly more similar to Europeans than are lower castes."

There is some evidence that a few millennia ago, a group of people with (Eastern) European genetic affinities migrated into the Indian subcontinent from the northwest. In the abstract to their paper Bamshad et al stated, "In the most recent of these waves, Indo-European-speaking people from West Eurasia entered India from the northwest and diffused throughout the subcontinent. They purportedly admixed with or displaced indigenous Dravidic-speaking populations. Subsequently they may have established the Hindu caste system and placed themselves primarily in castes of higher rank" [12]. However, critics point out that Andhra Pradesh might not be the best place for such a study. One of the upper castes, Kshatriyas, belongs to the miniscule part of Telugu population. Also, historically South Indian royal families had marital relationship with Central and East Indian royal families. In other words, Kshatriyas were not as isolated as Chenchu tribe. In the regions of present day Andhra Pradesh, the dominant and generally feudal castes were Reddys and Kammas though they were classified as Shudras. Also, terming Brahmins in South India as a proof of dominance of Indo-European people shows fundamental ignorance from researchers' part regarding the Brahmin migration to South India. From historical records it has been observed that the transition of South Indian kings from Buddhism, Jainism and non-Vedic Saivism to Brahmanical Hinduism resulted in Brahmins being imported from North India to perform religious duties. In addition to that, it has also been noted that many North Indian Brahmin families took refuge in South India escaping from religious persecution at the hands of invaders. This again questions researchers' competency in making such definite statements. Critics also point out that the European specific markers, however controversial might their origins be, is observed across the caste lines in North-West of India. The study also revealed another classic anthropological observation, that women are significantly more mobile in terms of caste and hierarchical class than men, who are barely socially mobile at all in terms of caste and hierarchical Social class. Genetic evidence reveals that over millennia men from higher casts have married women from lower castes, but women from higher casts have rarely married men from lower castes. Thus the researchers imply that caste and class to a large extent is perpetuated by women and has also thereby contributed to the minimal mixing of Aryan blood with the natives. Recent paper in Current Biology, Cordaux et. al. (2004) confirms the Bamshad (2001) results and concludes that the paternal lineages of Indian caste groups are primarily descendants of Indo-European speakers who migrated from Central Asia about 3,500 years ago.

However, other studies (Kivisild 2003a; Kivisild 2003b) have revealed that a high frequency of haplogroup 3 (R1a1) occurs in about half of the male population of Northwestern India and is also frequent in Western Bengal. These results, together with the fact that haplogroup 3 is much less frequent in Iran and Anatolia than it is in India, indicates that haplogroup 3 among high caste Telugus did not necessarily originate from Eastern Europeans. The high diversity of haplogroup 3 and 9 in India suggests that these haplogroups may have originated in India (Kivisild 2003a). (See also Colin Renfrew [13].)

Most of the pro-migration papers imply that R1a1 is the genetic marker that is representative of a migration, due to its high frequency in Eurasia. But an equally likely genetic marker is haplogroup L. This haplogroup is present in Greek, Turkish, Lebanese, Iranian, Central Asian, and Indian populations (and Europe, see Kivisild). This marker is found in locations where written sources record the presence of Indo-European languages and people: i.e. Greeks, Hittite, Mitanni, Iranians and Indians. Its peak frequency is found in Indo-Iranian populations. The 'Western Eurasian' components that are found in Indian mtDNA show a distribution closer to that found in the Southern Caucasus and Middle East than to that found in Eastern Europe. There is also the question of why one should assume only one Y haplogroup is representative of the Aryan gene pool. R1a1, R1b, J2, L and H - all of which are present in India and Central and West Asia - are all possibilities. However, haplogroup L has a very low level of diversity in the Punjab. This is suggestive of a recent migration or expansion event in the area, and is supported by the fact that the diversity of R1a1, J2 and haplogroup C is higher in the region. Haplogroup C is supposed to be the remmants of the "Out of Africa" migration of humans, but still retains a high level of diversity. Haplogroup L is also found in South India at relatively high freqencies and has been associated by some (along with J2) with the spread of farming and Dravidian languages.

Interestingly, studies show that there has been very little mixing of the male lines between castes/clans for some time. They show distinct haplotypes even though many clans within a region have similar haplogroups. For instance, Northwest Indians exhibit mainly haplogroups R1a1, R1b, J2 and L, yet there is very little sharing of haplotypes with other castes/clans in the same region. In fact according to the yhrd.org database, Jats (mainly Punjabi Sikhs) have more haplotypes in common with Germans, Balts, Slavs and Iranians (2%-10%, 1-5 haplotypes, mainly R1a1) than with some neighbouring castes in India and Pakistan. The question arises, if Aryans came from outside India and Pakistan, how is it that they were able to separate into distinct clans without any of the clans sharing a considerable percentage of haplotypes? [14] (Also, note that most Indo-European-speaking people exhibit a mixture of R1a1, R1b, I1a, I1b, E3b and J2. The Hindu text the Laws of Manu states that Punjabis are no longer Aryans since they do not follow the caste system. It would be interesting if this is reflected in the genetics.

autosomal markers

One more important marker for Caucasian ancestry in admixed populations may be taken into consideration: H2 haplotype of the gene MAPT. It is shown to be Caucasian in origin, and may work as a good estimator of European admixture. “The constancy of the H2 allele frequency in Caucasian populations from the Middle East to the Orkneys suggest that its origin in European populations is ancient and coincides with the colonization of Europe.” ([15]). MAPT represented “by two distinct lineages, H1 and H2, that have diverged for as much as 3 million years and show no evidence of having recombined”. “The H2 lineage is rare in Africans, almost absent in East Asians but found at a frequency of 20% in Europeans” ([16]). There are some “evidence suggesting that Homo neanderthalensis contributed the H2 MAPT haplotype to Homo sapiens” ([17]). H2 is found in many Pakistan populations ([18]).

Interestingly, map of the worldwide frequencies of ASPM (Brain Size Determinant in Homo sapiens) haplogroup D ("derived") ([19])matches surprisingly well the map of H2 haplotype distribution. “The frequency of haplogroup D chromosomes is ... 44% in Europeans and Middle Easterners”. “Estimated the coalescence age (i.e., time to the most recent common ancestor) of haplogroup D at 5800 years, with a 95% confidence interval between 500 and 14,100 years.” Of course one should take into consideration, that ASPM “haplogroup D ... rose to high frequency under strong positive selection”, thus Frequency of the ASPM haplogroup D is expected to be higher, than MAPT haplogroup H2. However, considering the facts that only few Pakistani populations were sampled and both markers (ASPM haplogroup D, MAPT haplogroup H2) are present not only in European, but in Middle Eastern populations too, one should consider distribution of these markers only as a suggestion of the eastward migration of “Caucasian peoples” (Europeans and/or Middle Easterners). Thus distribution of these markers taken alone can hardly prove specific Indo-Aryan migration or invasion.

Intriguingly, well-discussed CCR5 delta 32 mutation may be older, than suspected before ([20]), and was detected in 2900-year-old skeletal remains from different burial sites in central Germany and southern Italy with rather high allele frequency (11.9%) ([21]). Thus this mutation may work as a marker of European (vs. Middle Eastern) ancestry. According the 2002 Khaliq paper ([22]) frequency of the CCR5 delta 32 allele ranged from 0.62% to 3.57% in Pakistani ethnic groups, which is much lower than that found in European populations (10% average frequency), and similar to that in the Middle East. One of the possible explanations of such geographical distribution is the migration of the mutation carriers from the territory of high mutation frequency into the area where such mutation is absent.

Adapted from the Wikipedia article "Y chromosome", under the G.N U Free Docmentation License. Please also see http://en.wikipedia.org/wiki