How Did India's Linguistically Austroasiatic Khasi People End Up With Tibeto-Burman Genetics?

The Khasic languages are most closely related to the Austroasiatic Palaungic language of Myanmar, and the Khumic language of Northern Laos.

The Khasi people of Northeast India speak an Austroasiatic language, but one that is in a different subfamily than India's Munda speakers and the Mon-Khemer people of Southeast Asia. Yet, genetically they are more similar to Tibeto-Burman language family speakers. 

This is because their linguistic ancestors admixed with a first wave of Tibeto-Burman people resulting in their adoption of the Khasi language. But, they lack genetic traces of a second wave of Tibeto-Burman language speakers whose language replaced that of the Austroasiatic languages in the peoples they encountered.

Northeast India, with its unique geographic location in the midst of the Himalayas and Bay of Bengal, has served as a passage for the movement of modern humans across the Indian subcontinent and East/Southeast Asia. 

In this study we look into the population genetics of a unique population called the Khasi, speaking a language (also known as the Khasi language) belonging to the Austroasiatic language family and residing amidst the Tibeto-Burman speakers as an isolated population. The Khasi language belongs to one of the three major broad classifications or phyla of the Austroasiatic language and the speakers of the three sub-groups are separated from each other by large geographical distances. The Khasi speakers are separated from their nearest Austroasiatic language-speaking sub-groups: the “Mundari” sub-family from East and peninsular India and the “Mon-Khmers” in Mainland Southeast Asia. 

We found the Khasi population to be genetically distinct from other Austroasiatic speakers, i.e. Mundaris and Mon-Khmers, but relatively similar to the geographically proximal Tibeto Burmans. The possible reasons for this genetic-linguistic discordance lie in the admixture history of different migration events that originated from East Asia and proceeded possibly towards Southeast Asia. 

We found at least two distinct migration events from East Asia. While the ancestors of today’s Tibeto-Burman speakers were affected by both, the ancestors of Khasis were insulated from the second migration event. Correlating the linguistic similarity of Tibeto-Burman and Sino-Tibetan languages of today’s East Asians, we infer that the second wave of migration resulted in a linguistic transition while the Khasis could preserve their linguistic identity.

Debashree Tagore, et al., "Multiple migrations from East Asia led to linguistic transformation in NorthEast India and mainland Southeast Asia" Front. Genet. (October 11, 2022). The body text of the introduction provides more background about the Khasi people and the current understanding of their potential origins prior to this paper:

The Khasis are one of the few populations in the world that follow a matrilineal system of inheritance. Besides the linguistic similarity, anthropologists and archaeologists have established that the Khasis have cultural similarities with Mundaris and Mon-Khmer populations. It has been shown that they share similar stone tools and have similar death rituals of erecting memorial stones for the deceased (Gurdon 1914). Linguistically, the Khasi language is more similar to languages of the Mon-Khmer branch than those of the Mundari branch and linguists have often assigned Khasi and Mon-Khmer languages to the same group (Pinnow et al., 1942; Chazée 1999). Khasi language also bears lexical and morphological similarities to some Tibeto Burman languages (Longmailai 2015). Peiros suggested a significant number of words were similar between Proto Austroasiatics and Proto-Sino-Tibetans (Peiros 2011).

Nevertheless, the presence of ancient Austroasiatics (AA) speakers across NEI still remains a possibility. Our previous study (Tagore et al., 2021) on autosomal data of the Mundari and Mon-Khmer Austroasiatics indicated that in pre-Neolithic times, the ancestors of today’s Austroasiatic speakers had a widespread distribution possibly extending from Central India to Southeast Asia (SEA), further supported by Lipson et al. (2018). They were later in time fragmented and isolated to small pockets resulting in their present-day disjoint geographic distribution. What is intriguing is that given the widespread distribution of Austroasiatic speakers from Central India to SEA across NEI and the central location of the Khasis, it is possible that the Khasis will serve as a genetic link between the two Austroasiatic groups on either side of NEI.

There have been very few studies on the genetics of Khasi, so as to reach any plausible conclusions. One previous study on uniparental markers has proposed a genetic continuity between the Mundari Austroasiatics of Central India, Khasi-Khmuic, and Mon-Khmer (Reddy et al., 2007). Using multidimensional scaling of the pairwise FST distances calculated on Y-haplogroups of Austroasiatics and neighboring populations, they found the three Austroasiatic groups (Mundari, Khasi-Khmuic, and Mon-Khmer) to cluster together. They also found the Y haplogroup O-M95, restricted within the Austroasiatics and postulated to have originated in the Mundaris, is present in the Khasis at a frequency intermediate to that of Mundaris and Mon-Khmers. They suggested an initial presence of Austroasiatics in Central India with rapid migration to Southeast Asia via the Northeast corridor carrying the O-M95 haplogroup.

Wikipedia has this to say about the Khasi people in its introduction:

The Khasi people are an ethnic group of Meghalaya in north-eastern India with a significant population in the bordering state of Assam, and in certain parts of Bangladesh. Khasi people form the majority of the population of the eastern part of Meghalaya, that is Khasi Hills, constituting 78.3% of the region's population, and is the state's largest community, with around 48% of the population of Meghalaya. They are among the few Austroasiatic-speaking peoples in South Asia. The Khasi tribe holds the distinction of being one of the few remaining matriarchal tribes of the world. Under the Constitution of India, the Khasis have been granted the status of Scheduled Tribe.

India	1,427,711
Meghalaya	1,382,278
Assam	34,558
Bangladesh	85,120

About 1 million of the roughly 1.5 million Khasi people speak the Khasi language.

About 98.5% of the Khasi are either Christian (83.1%), mostly Catholic and Presbyterian, or adhere to their own indigenous Niam Khasi religion (15.4%) which has some similarities to deism. About 0.7% are Hindus, about 0.5% are atheists, and the remaining 0.3% include similar numbers of Buddhists and Muslims.