India is a country remarkable for its diversity; biological and human. The biological diversity owes itself to the country’s position at the trijunction of the African, the northern Eurasian and the Oriental realm; its great variety of environmental regimes, and its relative stability of biological production. It is this biological wealth that has attracted to the subcontinent many streams of people at different times, from different directions; bringing together a great diversity of human genes and human cultures. Whereas in other lands the dominant human cultures have tended to absorb or eliminate others, in India the tendency has been to isolate and subjugate the subordinated cultures, thereby augmenting cultural diversity. This tendency to nurture diversity has been favoured by the diversity of the country’s ecological regimes [Gadgil and Guha, 1992].
People migrate because of pulls from their destination and pushes in their homeland, often propelled along by some technological advantage. Thus in 16th century Europeans came to India in search of spices, pushed out by the little ice age that had gripped Europe, equipped with superior seagoing vessels and guns. That migration is well documented and understood; but it is the many earlier ones that have brought to India the bulk of human genes and cultural traits. It is our purpose in this paper to elucidate what we can of these many earlier migrations.
Role of Technology and Innovations
People have of course migrated out of India as well, but these out-migrations have been on a much smaller scale, and mostly over the last three centuries. This is related to the fact that India has never been the site of any significant technological innovations. A series of important innovations have, over the years taken place outside of India, innovations which have given an edge to people in control of these innovations, propelling major migrations [Habib, 1992].
In chronological order the most relevant of these include:
(i) Evolution of symbolic language, probably by the first modern Homo sapiens, in Africa, perhaps around 100 kybp (kybp = thousand years before present);
(ii) Husbanding of wheat, barley, cattle, pig in the mideast around 10 kybp;
(iii) husbanding of rice, buffalo in China and Southeast Asia around 8 kybp;
(iv) Domestication of horse in Central Asia around 6 kybp;
(v) Use of iron in Anatolia around 5 kybp;
(vi) Use of stirrup for horse riding in Central Asia around 2 kybp;
(vii) Use of gunpowder in China around 2 kybp;
(viii) Use of canons and guns in war in Arabia in 15 th century
Our theme then is that these manifold innovations to the west, east and north of the Indian subcontinent have propelled many waves of people onto our land, giving rise to what is genetically as well as culturally the most diverse society in the world. There are diverse lines of evidence for these migrations – genetic, linguistic archaeological, anthropological. We will endeavour to draw on all these disciplines to reconstruct the story of peopling of India.
The earliest migrants into India, perhaps 50 kybp may have been the Austric speaking Homo sapiens, with the advantage conferred by the mastery over a symbolic language. Their genetic footprints may be discerned in the trends evident in the 2nd P.C of the synthetic genetic map of Asia. The next major waves of migrations around 6 kybp may have been those of wheat cultivators from the middle east and the rice cultivators from China and south east Asia. The former are likely to have been Dravidian speakers and contributed to the trend evident in the 1st P.C. of the synthetic genetic map of Asia. the latter may have been Sino-Tibetan speakers who would have contributed further to the trend revealed by 2nd P.C. The latest major migration around 4 kybp may have included several waves of Indo-European speakers equipped with horses and iron technology.
What the Indian population is remarkable for is the segmentation of this large population into thousands of endogamous groups. The People of India data recognizes 4635 such ethnic communities. Many of these are however clusters of endogamous groups with similar traditional occupations and social status. The actual number of endogamous groups is decidedly much larger, of the order of 50 to 60 thousand (Joshi, Gadgil and Patil 1993; Gadgil and Malhotra 1983). This persistence of tribe like endogamous groups, characteristic of hunter-gatherer-shifting cultivation stage all over the world, in a complex agrarian, and now industrial society of India is a unique phenomenon. It seems to be a result of a peculiarly Indian tradition of subjugation and isolation, rather than the worldwide practice of elimination or assimilation of subordinated communities by the dominant groups.
Our mitochondrial DNA studies provide some notable insights into the structure of this social mosaic. For this purpose we chose two communities, Haviks and Mukris from the same district of Uttara Kannada. Haviks are a Brahmin group well known for their skills at growing multi-storeyed spice gardens of cardamom, pepper and betelnut. They also perform priestly functions, and are today prominent in many white collar occupations. Their current populations is around 100,000 individuals concentrated in an area of about 20,000 km2. The Mukri, on the contrary are members of a scheduled caste, earlier treated as untouchables. Their current population numbers around 9000 individuals concentrated in an area of 2000 km2. They continue to indulge in substantial amounts of hunting, gathering and fishing to this date and serve as unskilled labour on Havik and other farms.
These might have been the most massive migrations peopling India. Others have followed, largely from the west, through the Khyber pass on the northwestern frontiers of the subcontinent. These seem to have been propelled by superior weaponry, increasingly better control over horses and finally seagoing ships.
Such significant innovations may include some of the following. An important early development in weaponry was the composite angular bow which appeared in west Asia around 5 kybp. Bending through the length of the limb, releasing this bow string produced no kick leading to a smooth and accurate shot. The extremely long draw length of over 1 m led to a greatly enhanced cast. A crucial piece of equipment associated with control over horse is stirrup, which helps in balancing the rider and permits him to stand up to threw the lance. The earliest form of the stirrup was a string with two loops on either side for the rider’s foot. The first known instance of iron stirrups comes from China in sixth century A.D. reaching Iran by 7th century, and arriving in India with Turkish warriors in 11th century. Another significant invention was the iron horse shoe first known from Siberia in 9th Century A.D., reaching India with Turkish warriors in 13th Century A.D. The gunpowder was invented in China around 100 A.D. and slowly reached Iran, Arabia and finally Europe with Mongols around 1400 A.D. It reached India with the arrival of the first Mughal emperor Babur who used it in the first battle of Panipat in 1526 A.D..
Linguistically, Indians are classified into four major language families; Indo-European, Dravidian, Austroasiatic and Tibeto-Burman. Indo-European is the most widely spoken language family in India, particularly in northern, central and western India. Dravidian speakers are mainly confined to southern parts of the country. Austroasiatic speakers are dispersed mostly in the central and eastern parts, while the Tibeto-Burman speakers are concentrated in and around the foothills of the Himalayas and north east states. In addition to these major language families, there are a few isolated languages, such as Andamanese, spoken by the enigmatic tribal populations of Andaman and Nicobar Islands, and Nihali spoken in the pocket of the Western Ghats.
There are various evidences supporting the peopling of India by the early modern humans. It is well established that the modern human originated in Africa about 200,000 years before present (YBP). They started migrating out-of-Africa between 55,000 and 85,000 YBP. There are several thoughts regarding the cause and timing of this migration. One compelling view being put forward is based on geological finding. It states that there was a mega drought in East Africa between 135,000 and 75,000 YBP, when the water volume of Lake Malawi was reduced by at least 95%. The timing of this mega drought corresponds with the timing of the exodus of anatomically modern humans out-of-Africa along the southern coastal route. The firm establishment of the southern coastal route of modern human migration reveals India as a major corridor for early human migration. The anthropological, historical, linguistic and genetic evidence for early peopling of India is found imprinted all over the country.
Recently, archaeological evidence supporting the early peopling of India was discovered in the Kurnool district of Andhra Pradesh, one of the southern Indian states. This study shows that modern humans inhabited the country before and after the Toba eruption around 74,000 YBP. The evidence is in the form of stone tools. The stone tools of this study most likely resemble contemporaneous Homo sapiens technologies in Africa. Further, a partial cranium recovered from Narmada Basin was dated back to around 300,000 to 250,000 YBP.Over the past two decades, several independent studies have been carried out in various Indian populations with ancient and modern DNA using haploid and diploid markers. Almost all the studies found signs of early settlement by the first group of modern human venturing out-of-Africa and very recent gene flow from west and east Eurasia.
India is a land of social stratifications, such as castes, tribes and religious groups. Although the precise date of origin for the caste system in India is unclear, the written evidence about the organisation of the caste system exists in the Rig Veda, which was written between 1700 and 1100 BC. Caste is a social hierarchy based on occupation. There are four broad categories of castes in Hindu society: Brahmin, Kshatriya, Vaishya and Sudra. Each caste is known to perform a specific duty. Brahmins perform rituals and are in charge of teaching society; Kshatriyas are rulers and warriors, and are involved in ruling and defending the territories; Vaishyas are cultivators and businessmen; Sudras rank last in society and are labourers by profession. Each caste is further subdivided into smaller units generally known as subcastes, which in turn are further divided into multiple exogamous clans known as Gotras. The caste system governs all social, religious and economic activities of the people. The long-term social boundaries and endogamy practice among all social groups has given birth to diverse, population-specific social traditions and the development of distinct linguistic dialects.The divergent endogamous cultural and social structures are helpful in understanding genetic variation among the populations and their ancestry.
Emergence of caste system in India and its amalgamation with the waves of migrations
A noteworthy view can be put forward on the development and maintenance of the caste system on the basis of genetic observations .The ancestral tribes might have given birth to various subtribes over time. Some of the subtribes might have migrated and gradually established themselves as lower caste groups through better knowledge of procuring necessary resources. Further, the empowerments of some of the lower caste group might have helped them to establish themselves as middle caste groups. Increased mastery over technological and economic measures among some of the middle caste group might have facilitated attainment of the upper caste level (Figure), thus giving rise to a complete caste system. Hence, a person’s profession became the symbol of the caste to which he or she belonged. As time passed, the caste system might have fortified itself in society by dividing populations into several endogamous pockets, and has undoubtedly played an essential role in shaping present day Indian genetic architecture. Furthermore, India has witnessed several waves of immigrations. The immigrants were absorbed into different hierarchal levels of the caste system .
Schematic showing the emergence of the caste system in India and its amalgamation with the waves of migrations.
In addition to the large number of indigenous populations, India has experienced immigration of several populations in the past, further adding to the complexities of Indian population structure. Among the recent migrants, we have extensively studied Siddi, Muslim and Jewish populations inhabiting India.
The Siddis are mainly found in three Indian states – Gujarat, Karnataka and Andhra Pradesh -and have typical African features such as dark skin, curly hair, broad nose, and so on. Historically, it is known that they were brought to India by Portuguese traders between the 17th and 19th centuries and sold to the Nawabs and the Sultans of India to serve as soldiers and slaves. Earlier, we showed the presence of a Y-chromosome Alu insertion; an African-specific marker, in 40% of Siddis. The mitochondrial DNA hypervariable sequence also confirmed the Siddis’ affinity with Africans. However, there was no high resolution study pertaining to the origin, affinity and genetic structure of the Indian Siddis. In an attempt to reveal these issues together, we screened the Siddi populations from the Junagarh district of Gujarat and UttaraKannad district of Karnataka using mtDNA and Y-chromosomal and high density autosomal markers. Along with Siddis, six populations with geographical proximity to Siddis have also been studied to capture a scenario of gene flow. Our analysis revealed that the Siddi population has a combined ancestry (that is, 70% African and 30% Indian and European). We further estimated that the Siddis have admixed with the neighbouring Indian populations for about 200 years ago (eight generations). Our genetic finding coincides with the historical record of the arrival of Siddi people in India.
Y-chromosome results revealed the presence of African-specific haplogroups. Further, extensive investigation on Y-STRs revealed that the Siddis are the direct descendants of the Bantu-speakers of sub-Saharan Africa. We observed an Indian-specific gene pool in Siddis but the Siddi-specific gene pool was not observed in neighbouring Indian populations. This firmly suggests the unidirectional gene flow from the Indian population to the Siddis, confirming the rigidity of the Indian social structure.We also predicted that the approximate number of males Siddis who reached India between the 17th and 19th centuries was about 1,500.
Another well-documented recent migration is that of the Muslim population. The Arab Muslims established their first kingdom in India by conquering Sindh in 711 AD. During the 13th century, a Turkic kingdom was established in Delhi and in the 16th century the famous Mughal Empire appeared in India. The Muslim immigrations were especially male-mediated in the form of invaders from Iran and Arabia. The majority of the present day Indian Muslims are believed to be the descendants of converts from local Hindu (caste and tribal) populations. Thus, we undertook an extensive study among Indian Muslims from diverse geographical regions to trace their genetic structure, origin and affinity using Y-chromosome and mtDNA markers. Even though we observed their genetic affinity with indigenous Indian non-Muslim populations, a small frequency of the Middle Eastern ancestry was also noticed. Therefore, the genetic analysis of Indian Muslims shows the spread of Muslims in India was mainly mediated by cultural adaptation linked with minor gene flow from the Middle East.
Based on the extensive genetic studies carried out on different Indian populations, we can infer that each of them is a genetically distinct ethnic population in part due to high levels of endogamy. High-resolution genetic studies revealed the in situ origin of several deep-rooting mtDNA lineages in India, suggesting that Indian populations are genetically unique and harbour the second highest genetic diversity after Africans. The genomic complexity brought on by endogamous practice for thousands of years, language shifts and sex-specific admixture are highly challenging to study and need further, extensive genetic characterization. The complex genomic architecture of Indian populations adds difficulty in understanding diseases and implementing preventive measures. The accumulation of various mutations due to endogamy leads to recessive diseases in the Indian population, which further increases the total disease burden of the country. Several questions pertaining to the origin of the caste system, the arrival and spread of the major language families and finding disease-associated genetic variants require effective approaches combining various disciplines such as archaeology, historical linguistics, genetics, bioinformatics and pharmacology. Even though studies with high density markers have added much to the knowledge about the Indian populations, whole genome approaches are expected to answer many of the existing questions.
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