New Delhi: Vice-President Venkaiah Naidu on Friday suggested that communities enjoying reservation be divided into sub-categories, enjoying sub-quotas based on population shares, for a more equitable distribution of reservation benefits.

Such a measure would benefit the most backward communities among the Scheduled Castes and Scheduled Tribes, often left out of the reservation pie now because of the dominance of the relatively advanced communities within the group.

"There should be a national debate on sub-categorisation of social groups to reach the un-reached," Naidu said after releasing a book, Social Exclusion and Justice in India, by P.S. Krishnan.

Ten states including Bengal have already sub-categorised their Other Backward Class quotas. The Narendra Modi government decided in September to sub-categorise the central OBC quota too and set up a commission in October to suggest how it should be done.

But no sub-categorisation now exists in the Scheduled Caste and Scheduled Tribe quotas, with the Supreme Court striking down such initiatives by some states, such as Punjab and Andhra Pradesh in the 1990s, as unconstitutional.

To sub-categorise the Dalit and tribal reservation pie, the government will have to either seek a review of the apex court's years-old judgment or, more plausibly, amend the Constitution.

"Caste is a blot on humanistic philosophy.... Within reservation, castes and sub-castes should get their share. We must evolve a consensus," Naidu said.

He said there was a demand for sub-categorisation among the most deprived sections, and tried to allay any possible anxiety among the dominant Dalit and tribal sub-groups.

"There is no question of doing harm. It is about taking care of your brothers. When reservation was introduced, people said Hindus were being divided. But it was not (true)," Naidu said.

Dalit communities like Valmikis, Pasis, Dhobis and Koris in Uttar Pradesh are said to resent their Jatav or Chamar brethren's dominance over the reservation benefits. Among the Scheduled Tribes, there is rancour against the Meena caste in Rajasthan.

Krishnan, the author of the book launched, was secretary in the then welfare ministry in 1990 when the V.P. Singh government implemented the Mandal Commission report, providing for OBC reservation.

In the book, he has stressed efforts towards economic and educational improvement of Dalit and tribal populations, and demanded statutory status for the provision for earmarked public expenditure on these communities' development.

Although the government is supposed to set aside 15 and 7.5 per cent of the budget, respectively, for the Scheduled Caste Sub-Plan and the Scheduled Tribe Sub-Plan, focused on residential schooling, health, nutrition and other development avenues, the spending remains much less.

Krishnan has advocated distribution of unused land among landless Dalit and tribal families. Naidu supported the suggestions.

The book also explores the nuances of the Gandhi-Ambedkar debate on the status and liberation of Dalits. It provides insights into the legal, economic and cultural structures that lie behind the caste system and untouchability.