The Purusha Sukta, Rig Veda 10.90, describes the gods sacrificing a cosmic being, Purusha, whose dismembered body becomes the created world, with the hymn's final verses stating that his mouth became the Brahmin, his arms the Kshatriya, his thighs the Vaishya, and his feet the Shudra. Read as an origin account, the passage has long been treated as scripture's own explanation for the varna system, the fourfold social division later elaborated into caste.
B. R. Ambedkar, the Dalit jurist who chaired the drafting of India's constitution, made the hymn central to his case against caste's religious legitimacy. In Annihilation of Caste, the 1936 speech he could not deliver because its host organization withdrew its invitation over the text's contents and then published at his own expense, he argued that caste rests on scriptural authority precisely of this kind, so that reforming caste without confronting the texts that sanctify it, the Vedas and shastras among them, could not succeed. He read the Purusha Sukta as religion supplying a body for social hierarchy to wear, not describing a natural or moral order.
Later Dalit theology has pressed the same passage further, treating the sacrificed Purusha's feet, the origin named for Shudras and by extension those later cast outside the four varnas altogether, as a starting point for reading Purusha's suffering body itself as standing with the oppressed rather than ranking them beneath the rest. Other modern and reformist readings take the opposite route, arguing the hymn describes function rather than birth status and that hereditary caste is a later corruption of a division the verse never intended as fixed by descent.