Pratiloma is a Sanskrit term used in the Manusmriti, that is the Laws of Manu (Shraddhadeva Manu), to describe a hypogamous union between a high born woman and a man of a lower standing (by birth) relative to the respective woman.
[1] Manu explains that the evolution of different castes among mankind occurred due to the union of two persons who did not belong to the same rung in the caste or class ladder (by birth and not wealth or status in society) relative to each other.
[2] According to Manu, marriage within the same caste, that is, between two persons who belong to the same rung in the ladder, is excellent.
[1] Manu bitterly criticises and condemns Pratiloma unions which were considered as "going against the hair or grain" and holds them responsible for the degeneration of the parties involved, subsequent to the union.
[3] Manu pronounces that the Pratiloma unions cause a confusion of the castes and lists six combinations that happen at the initial stage (ordered hierarchically from high to low),[4] Similarly, there are six castes listed for the reverse union or Anuloma where a high born male unites with a woman of a lower standing (relative to the man).