Vedas are apaurusheya, which means they are not compilations of human knowledge. Vedic knowledge comes from the spiritual world, from Lord Krishna, the Supreme Personality of Godhead. In the beginning of the universe the first living creature is Lord Brahma.  He received the Vedic knowledge from Krishna. ( Brahma - Samhita )

Vedas are compared to a desire tree because they contain all things knowable by man. They deal with mundane necessities as well as spiritual realization. Above and beyond all departments of knowledge there are specific directions for spiritual realization. Regulated knowledge involves a gradual raising of the living entity to the spiritual platform, through varna (brahmana - intellectual, kshatriya - ruler, vaishya - merchant, shudra - worker) and asrama (brahmacharya - student, grihastha - family, vanaprastha - retired, sannyasa - renounced). The highest spiritual realization is knowledge that the Personality of Godhead is the reservoir of all pleasures, and spiritual tastes.

Formerly there was only one Veda of the name Yajur. The sacrifices mentioned in the Vedas were means by which the people's occupations according to their orders of life (namely brahmacharya, grihastha, vanaprastha and sannyasa) could be purified.

To simplify the process of understanding and performing vedic rituals, Vyasadeva (the empowered incarnation of Krishna) divided the one Veda into four, Rg (prayers), Yajur (hymns for oblations), Sama (same prayers and hymns in meters for singing), Atharva (body/world maintenance and destruction) in order to explain them to civilized society.

Thus the original source of knowledge is the Vedas. There are no branches of knowledge either mundane or transcendental, which do not belong to the original texts of the Vedas. They have simply been developed into different branches. They were originally rendered by great seers ( Rshis , Sages ). In other words, the Vedic knowledge broken into different branches by different disciplic successions (known as shakhas) has been distributed all over the world. No one, therefore, can claim independent knowledge beyond the Vedas.

Yajur Veda     Rg Veda     Sama Veda     Atharva Veda