Most important change was the evolution of caste system. Various sub castes evolved in addition to the traditional four-castes. The Brahmanas and Kshatriyas emerged as the two leading castes out of the general mass of population, known as vaisyas. The vaisyas were superior to the sudras but their position was steadily deteriorating. The Aitaraya Brahmana clearly indicates the absolute dependence of vaisyas on the two higher classes. The Sudras were held in great contempt.
The Brahmanas of the later Vedic age were the intellectual and priestly class. The Brahmanas retained a high standard of excellence and knew the details of the rituals. The kshatriyas were the fighting class in the society. War, conquest, administration of the kingdom was the principal duties of this class. By their superior learning some kshatriyas raised themselves to the status of a Brahmana. They composed hymns and performed sacrifices and also challenged the supremacy of Brahmanas.
Two Kshatriya kings Janak and Viswamitra attained the status of Rishi. For a long time the kshatriyas resisted the supremacy of the Brahmanas and claimed that the priest was only a follower of the king. Vaisyas were engaged in trade, industry and agriculture, and animal husbandry. They are debarred from the privileges which were enjoyed by the Brahmanas and kshatriyas. However the richer people among the vaisyas known as Sresthin were highly honored in the royal court.
The condition of the Sudras was very miserable. They had to serve the other three castes. They were untouchables. They had no right to approach the sacred fire, i.e., perform sacrifice, or to read the sacred texts. They were further denied the rite of burning the dead body. The structure of the caste system became hereditary.
The women lost their high position which they had in the Rig Vedic Age. They were deprived of their right to the Upanayana ceremony and all their sacraments, excluding marriage, were performed without recitation of Vedic mantras. Polygamy prevailed in the society. Many of the religious ceremonies, formerly practiced by the wife, were now performed by the priests. She was not allowed to attend the political assemblies. Birth of a daughter became undesirable—for she was regarded as a source of misery. The custom of child marriage and dowry crept in. The women lost their honored position in the society.