[5][6][7] The social and religious patterns of Bengal had historically been distinctively different from those in the orthodox Hindu heartland of North India and this impacted on how the caste system developed there.

Bengal, being located east of the traditional Aryavarta (Aryan) region between the Ganges and Yamuna rivers, remained insulated from the full impact of Brahminical orthodoxy for many centuries.

Surnames like Datta, Dama, Palita, Pala, Kunda (Kundu), Dasa, Naga and Nandin are now confined to Kayasthas of Bengal but not to brahmanas.

So there is every probability that a number of brahmana families were mixed up with members of other varnas in forming the present Kayastha and Vaidya communities of Bengal.Sharma also mentions that D. R. Bhandarkar "has pointed out that identical surnames are used by the Nagara-brahmanas".

[9] Referring to Naishadha Charita and Usanas-samhita smriti, Rabindra Nath Chakraborty mentions that according to these two medieval texts, "the Kayasthas were descended from Nagara Brahmin who had a large settlement in Bengal in the eighth century AD".

The Pala, Sena, Chandra, and Varman dynasties and their descendants, who claimed the status of Kshatriya, "almost imperceptibly merged" with the Kayastha caste, "which also ranked as shudras".

[3] Eaton mentions that the Kayasthas continued as the "dominant landholding caste" even after the Muslim conquests on the Indian subcontinent, and absorbed the descendants of the region's old Hindu rulers.

A report by Herbert Hope Risley and Edward Albert Gait cited their failure to observe scriptural dogma and rejection of the sacred thread as the reason for the loss of their upper-caste status.

One of the earliest such verdicts in Rajcoomar Lal v. Bissessur Dayal (1884), adjudged the Shudra designation but was influenced by a 'semantic-historicist' argument that Bengali Kayasthas had been degraded from an earlier Kshatriya status.

[25][24]: 343  Nabaparna Ghosh states that these verdicts relied on the premise that Bengali Kayasthas were different from those of the United Provinces and Bihar, as they did not initiate themselves to sacred threads nor performed rituals at the time of adoption.

Judges in these verdicts cited the lack of these rituals in Bengal as an example of its distinctiveness from other provinces, territorializing the Bengali Kayastha caste identity.

[24]: 343–344 According to Ghosh, the 'territorialization' of caste by Calcutta High court validated the Bengali Kayasthas as a distinct homogenous identity in equal status to the Shudras.

According to Bellenoit, "although Tagore had Bengal specifically in mind, he argued that the Dutts, Ghoshs and Guhas were of Kshatriya origin, again citing their 'respectability and prominence in administration and overall rates of literacy'".

Abdul Sharar, who was well acquainted with them also supported their claims of twice-born (Kshatriya and Vaishya origin) citing their high literacy rate which a Shudra caste could not have achieved.

At different times and in different places, those labelled Kayastha were accorded the same status as Brahmins, Kshatriyas or Sudras, and there was even a claim that they formed a fifth varna within the Hindu caste structure".

[38] According to Swarupa Gupta this legend was ... fitted into a quasi-historical, sociological narrative of Bengal and deployed to explain the realities of caste and sub-caste origins and connections during the late nineteenth and early twentieth century.

[31] A modern genetic study evaluating this myth found that "individuals belonging to some of the Kayastha lineages, whether termed Kulin or Moulik in later times, show genetic relatedness with present-day populations in Uttar Pradesh (Bose, Pal), while others show a significant genomic contribution from South India, or do not yield any informative signal on the basis of available Indian populations for comparisons (Nandi).