Brahmins whose duty was priesthood, took to other vocations over a period of time.
Some took to other professions fully while some continued both priestly duties and other professions.
Yet some remained only with priestly duties, like the Vaidika Brahmins.
Brahmins, contrary to what is being projected as outsiders, were a part of Sanatana Dharma and were present throughout Bharatavarsha.
Yet there were migrations of the community from one part of Bharatavarsha to another.
As Sanatana Dharma extended throughout the world there is no question of anyone coming from outside into India.
For instance the migration of Niyogi Brahmins from Multan, now in Pakistan into India is not real migration into India as Brahmins were living in Bharatavarsha earlier to this period as part of Pancha Dravidas.
One of the Brahmin groups is the Aaruvelu Brahmins.
They speak Telugu but are spread throughout India.
Aaruvelu means six thousand.
Six thousand Brahmins are grouped to form Aaruvelu Brahmins.
Essentially there is no difference among Brahmins.
Different names have been assigned based on the geographical locations where they settled, the additional duties they undertook, and number of families that constitute a group.
Thus we have Vadamas of Tamil Nadu who settled on the Northern banks of River Cauvery,
Vaathima a, who took primarily to priestly duties like Vaidika Brahmins and Astasahasram which consists of Eight Thousand families of Brahmins like the Aaruvelu Brahmins….
‘The Smarta Brahmins in Andhra Pradesh can be grouped into two major divisions formed about a thousand to 700 years ago (most probably during Kakatiya rule), Niyogi and Vaidiki, besides the smaller group of Bhatt. This classification is based on their inherent ability and Masterity in Administration, Spiritual Practices and cooking respectively.
Traditionally believed to have descended from Lord Parasurama, Niyogi Brahmins are those Brahmins who are into various secular vocations including military activities and gave up religious vocation, especially the priesthood just like Bhumihar Brahmins in north India who largely gave up priesthood. There is a lot of brotherhood between Niyogi Brahmins and Bhumihar Brahmins. The Bhumihar Brahmins, of whom many, though not all, belong to the Saryupareen Brahmin division of Kanyakubja Brahmins. The Bhumihar Brahmins were established when Parashurama destroyed the Kshatriya race, and he set up in their place the descendants of Brahmins, who, after a time, having mostly abandoned their priestly functions (although some still perform), took to land-owning.’
There are some references.
One states that Sage Viswamitra had his fifty sons ostracised to Dravida Desa for questioning his authority and these people intermarried with the Dravidas.
One of their descendants, Apasthamba compiled the Vedas in yet another form in the form of Sutras, called the Apasthamba Sutras.
This sutra incorporates some practices of the Dravidians like the wearing of Mangal Sutra in a Marriage.
Reference and Citation.