Peopling of India

Early hominins of Acheulean period

The presence of intelligent hominins in the subcontinent may stretch as far back as 1,500,000 ybp to the Acheulean period.

Ancestral South Indians and Ancestral North Indians

Reich et al. (2009) discerned two major ancestral components in India, namely the Ancestral North Indians (ANI) which is "genetically close to Middle Easterners, Central Asians, and Europeans," and the Ancestral South Indians (ASI) which is clearly distinct from ANI and "not closely related to groups outside the subcontinent." According to Basu et al. (2016), the ASI are earliest settlers in India, possibly arriving on the southern exit wave out of Africa. These two groups mixed in India between 4,200 and 1,900 years ago (2200 BCE-100 CE), whereafter a shift to endogamy took place, possibly by the enforcement of "social values and norms" by the "Hindu Gupta rulers."

Moorjani et al. (2013) describe three scenarios regarding the bringing together of the two groups:

According to Moorjani et al. (2013), the ANI and the ASI were plausibly present "unmixed" in India before 2,200 BC.

According to Basu et al. (2016), mainland India harbors two additional distinct ancestral components which have contributed to the gene pools of the Indian subcontinent, namely Ancestral Austro-Asiatic (AAA) and Ancestral Tibeto-Burman (ATB). According to Basu et al. (2016), the populations of the Andaman Islands archipelago form a distinct, fifth ancestry, which is "coancestral to Oceanic populations." According to Reich et al. (2009), "the indigenous Andaman Islanders are unique in being ASI-related groups without ANI ancestry."

Pre- or post-Toba

The dating of the earliest successful migration modern humans out of Africa is a matter of dispute. It may have happened either pre- or post-Toba, a catastrophic volcanic eruption that took place between 69,000 and 77,000 years ago at the site of present-day Lake Toba. Stone tools discovered below the layers of ash disposed in India at Jwalapuram, Andhra Pradesh, may point to a pre-Toba dispersal, but the exact source of these tools is disputed. An indication for post-Toba is haplo-group L3, that originated before the dispersal of humans out of Africa, and can be dated to 60,000–70,000 years ago, "suggesting that humanity left Africa a few thousand years after Toba."

It has been hypothesized that the Toba supereruption about 74,000 years ago destroyed much of India's central forests, covering it with a layer of volcanic ash, and may have brought humans worldwide to a state of near-extinction by suddenly plunging the planet into an ice-age that could have lasted for up to 1,800 years. If true, this may "explain the apparent bottleneck in human populations that geneticists believe occurred between 50,000 and 100,000 years ago" and the relative "lack of genetic diversity among humans alive today."

Since the Toba event is believed to have had such a harsh impact and "specifically blanketed the Indian subcontinent in a deep layer of ash," it was "difficult to see how India's first colonists could have survived this greatest of all disasters." Therefore, it was believed that all humans previously present in India went extinct during, or shortly after, this event and these first Indians left "no trace of their DNA in present-day humans" - a theory seemingly backed by genetic studies.

Pre-Toba tools

Research published in 2009 by a team led by Michael Petraglia of the University of Oxford suggested that some humans may have survived the hypothesized catastrophe on the Indian mainland. Undertaking "Pompeii-like excavations" under the layer of Toba ash, the team discovered tools and human habitations from both before and after the eruption. However, human fossils have not been found from this period, and nothing is known of the ethnicity of these early humans in India. Recent research also by Macauly et al. (2005) and Posth et al. (2016), also argue for a post-Toba dispersal.

Post-Toba Southern Coastal dispersal

By some 70,000 years ago, during the last glacial period (Würm glaciation) and at the onset of the socalled Paleolithic revolution, a part of the bearers of mitochondrial haplogroup L3 migrated from East Africa into the Near East.

It has been estimated that from a population of 2,000 to 5,000 individuals in Africa, only a small group, possibly as few as 150 to 1,000 people, crossed the Red Sea. The group that crossed the Red Sea travelled along the coastal route around the coast of Arabia and Persia until reaching India, which appears to be the first major settling point. Geneticist Spencer Wells says that the early travellers followed the southern coastline of Asia, crossed about 250 kilometres (155 mi) of sea, and colonized Australia by around 50,000 years ago. The Aborigines of Australia, Wells says, are the descendants of the first wave of migrations.

"Negritos"

"Negritos" is a term used to characterize some tribal populations in southern India, including the Andamaneses of today, who share physical similarities with Africans. Because of these similarities, the "negritos" were thought to be direct descendents from the first African settlers.

The appropriateness of using the label 'Negrito' to bundle together peoples of different ethnicity based on similarities in stature and complexion has been challenged. The Negrito peoples are more likely descended from the Australoid-Melanesian settlers of Southeast Asia. Vishwanathan et al. (2004) conclude that "the tribal groups of southern India share a common ancestry, regardless of phenotypic characteristics, and are more closely related to other Indian groups than to African groups." According to Vishwanathan et al. (2004), the typical "negrito" features could also have been developed by convergent evolution. According to Gyaneshwer Chaubey and Endicott (2013), "At the current level of genetic resolution, however, there is no evidence of a single ancestral population for the different groups traditionally defined as 'negritos."

Andamese people

The Andaman islanders are grouped among the "negritos." According to Reich et al. (2009), ASI, 'Proto-East-Asia' and Andaman islanders split around 1,700 generations ago. Yet, according to Chaubey and Endicott (2013), the Andaman Islands were settled less than 26,000 years ago, by people who were not direct descendants of the first migrants out of Africa. According to Wang et al. (2011),

...the Andaman archipelago was likely settled by modern humans from northeast India via the land-bridge which connected the Andaman archipelago and Myanmar around the Last Glacial Maximum (LGM), a scenario in well agreement with the evidence from linguistic and palaeoclimate studies.

60% of all Indians share the mtDNA haplogroup M, which is universal among Andamanese islander Adivasis, and might be a genetic legacy of the postulated first Indians.

L-M20

According to Spencer Wells, the "earliest significant settlement of India," after the earliest settlement of India, happened circa 30,000 years ago, by a clan which carried haplogroup M20, which is found at its highest frequency in south India. According to Spencer Wells, this was male migration, with typically migrating males mating with local woman, thereby spreading ancient maternal chromosomes combined with the newer male chromosomes.

Holocene

After the last Glacial maximum, human populations started to grow and migrate. With the invention of agriculture, the socalled Neolithic revolution, larger amounts of people could be sustained. The use of metals (copper, bronze, iron) further changed human ways of life, giving an initial advance to early users, and aiding further migrations, and admixture.

Dravidians

According to David McAlpin, the Dravidian languages were brought to India by immigration into India from Elam. According to Renfrew and Cavalli-Sforza, proto-Dravidian was brought to India by farmers from the Iranian part of the Fertile Crescent. According to Mikhail Andronov, Dravidian languages were brought to India at the beginning of the third millennium BCE.

Kivisild et al. (1999) note that "a small fraction of the West Eurasian mtDNA lineages found in Indian populations can be ascribed to a relatively recent admixture." at ca. 9,300 ± 3,000 years before present, which coincides with "the arrival to India of cereals domesticated in the Fertile Crescent" and "lends credence to the suggested linguistic connection between the Elamite and Dravidic populations."

According to Gallego Romero et al. (2011), their research on lactose tolerance in India suggests that "the west Eurasian genetic contribution identified by Reich et al. (2009) principally reflects gene flow from Iran and the Middle East." Gallego Romero notes that Indians who are lactose-tolerant show a genetic pattern regarding this tolerance which is "characteristic of the common European mutation." According to Romero, this suggests that "the most common lactose tolerance mutation made a two-way migration out of the Middle East less than 10,000 years ago. While the mutation spread across Europe, another explorer must have brought the mutation eastward to India – likely traveling along the coast of the Persian Gulf where other pockets of the same mutation have been found."

According to Palanichamy et al. (2015), "The presence of mtDNA haplogroups (HV14 and U1a) and Y-chromosome haplogroup (L1) in Dravidian populations indicates the spread of the Dravidian language into India from west Asia."

Asko Parpola, who regards the Harappans to have been Dravidian, notes that Mehrgarh (7000 BCE to c. 2500 BCE), to the west of the Indus River valley, is a precursor of the Indus Valley Civilisation, whose inhabitants migrated into the Indus Valley and became the Indus Valley Civilisation. It is one of the earliest sites with evidence of farming and herding in South Asia. According to Lukacs and Hemphill, while there is a strong continuity between the neolithic and chalcolithic (Copper Age) cultures of Mehrgarh, dental evidence shows that the chalcolithic population did not descend from the neolithic population of Mehrgarh, which "suggests moderate levels of gene flow." They further noted that "the direct lineal descendents of the Neolithic inhabitants of Mehrgarh are to be found to the south and the east of Mehrgarh, in northwestern India and the western edge of the Deccan plateau," with neolithic Mehrgarh showing greater affinity with chalocolithic Inamgaon, south of Mehrgarh, than with chalcolithic Mehrgarh.

Austroasiatic

According to Ness, there are three broad theories on the origins of the Austroasiatic speakers, namely northeastern India, central or southern China, or southeast Asia. Multiple researches indicate that the Austroasiatic populations in India are derived from (male) migrations from southeast Asia during the Holocene. According to Van Driem (2007),

...the mitochondrial picture indicates that the Munda maternal lineage derives from the earliest human settlers on the Subcontinent, whilst the predominant Y chromosome haplogroup argues for a Southeast Asian paternal homeland for Austroasiatic language communities in India.

According to Chaubey et al. (2011), "AA speakers in India today are derived from dispersal from Southeast Asia, followed by extensive sex-specific admixture with local Indian populations." According to Zhang et al. (2015), Austroasiatic (male) migrations from southeast Asia into India took place after the lates Glacial maximum, circa 10,000 years ago. According to Arunkumar et al. (2015), Y-chromosomal haplogroup O2a1-M95, which is typical for Austrosiatic speaking peoples, clearly decreases from Laos to east India, with "a serial decrease in expansion time from east to west," namely "5.7 ± 0.3 Kya in Laos, 5.2 ± 0.6 in Northeast India, and 4.3 ± 0.2 in East India." This suggests "a late Neolithic east to west spread of the lineage O2a1-M95 from Laos."

According to Riccio et al. (2011), the Munda people are likely descended from Austroasiatic migrants from southeast Asia. According to Ness, the Khasi probably migrated into India in the first millennium BCE.

Indo-Aryans

The Indo-Aryan migration theory explains the introduction of the Indo-Aryan languages in the Indian subcontinent by proposing migrations from the Sintashta culture through Bactria-Margiana Culture and into the northern Indian subcontinent (modern day India, Pakistan and Nepal). It is based on linguistic similarities between northern Indian and western European languages, and supported by archeological and anthropological research. They form part of a complex genetical puzzle on the origin and spread of the various components of the Indian population.

The Indo-Aryan migrations started in approximately 1,800 BCE, after the invention of the war chariot, and also brought Indo-Aryan languages into the Levant and possibly Inner Asia. It was part of the diffusion of Indo-European languages from the proto-Indo-European homeland at the Pontic steppe, a large area of grasslands in far Eastern Europe, which started in the 5th to 4th millennia BCE, and the Indo-European migrations out of the Eurasian steppes, which started approximately in 2,000 BCE.

The theory posits that these Indo-Aryan speaking people may have been a genetically diverse group of people who were united by shared cultural norms and language, referred to as aryā, "noble." Diffusion of this culture and language took place by patron-client systems, which allowed for the absorption and acculturalisation of other groups into this culture, and explains the strong influence on other cultures with which it interacted.

The idea of an Indo-Aryan immigration was developed shortly after the discovery of the Indo-European language family in the late 18th century, when similarities between western and Indian languages had been noted. Given these similarities, a single source or origin was proposed, which was diffused by migrations from some original homeland. This linguistic argument is complemented with archaeological, literary, and cultural evidence, and research and discussions on it continue.

The Proto-Indo-Iranians, from which the Indo-Aryans developed, are identified with the Sintashta culture (2100–1800 BCE), and the Andronovo culture, which flourished ca. 1800–1400 BCE in the steppes around the Aral sea, present-day Kazakhstan, Uzbekistan and Turkmenistan. The proto-Indo-Iranians were influenced by the Bactria-Margiana Culture, south of the Andronovo culture, from which they borrowed their distinctive religious beliefs and practices. The Indo-Aryans split off around 1800-1600 BCE from the Iranians, whereafter the Indo-Aryans migrated into the Levant and north-western India.

Tibeto-Burmese

According to Cordaux et al. (2004), the Tibeto-Burmans possibly came from the Himalayan and north-eastern borders of the subcontinent within the past 4,200 years.

A wide variety of Tibeto-Burman languages are spoken on the southern slopes of the Himalayas. Sizable groups that have been identified are the West Himalayish languages of Himachal Pradesh and western Nepal, the Tamangic languages of western Nepal, including Tamang with one million speakers, and the Kiranti languages of eastern Nepal. The remaining groups are small, with several isolates.

The Newar language (Nepal Bhasa) of central Nepal has a million speakers and a literature dating from the 12th century, and nearly a million people speak Magaric languages, but the rest have small speech communities. Other isolates and small groups in Nepal are Dura, Raji–Raute, Chepangic and Dhimalish. Lepcha is spoken in an area from eastern Nepal to western Bhutan. Most of the languages of Bhutan are Bodish, but it also has three small isolates, 'Ole ("Black Mountain Monpa"), Lhokpu and Gongduk and a larger community of speakers of Tshangla.

Crossovers in languages and ethnicity

One complication in studying various population groups is that ethnic origins and linguistic affiliations in India match only inexactly: while the Oraon adivasis are classified as an Australoid group, their language, called Kurukh, is Dravidian. The Nicobarese are considered to be a Mongoloid group, and the Munda and Santals Adivasi are Australoid groups, but all four speak Austro-Asiatic languages. The Bhils and Gonds Adivasi are frequently classified as Australoid groups, yet Bhil languages are Indo-European and the Gondi language is Dravidian.

Debate

The peopling of India is a contentious area of research and discourse, due to the debate on topics such as the Indo-Aryan migration theory.