The caste system is far from a rigid system in which the position of each component caste is fixed for all time. Movement has always been possible, and especially so in the middle regions of the hierarchy. A low caste was able, in a generation or two, to rise to a higher position in the hierarchy by adopting vegetarianism and teetotalism, and by Sanskritizing its ritual and pantheon. In short, it took over, as far as possible, the customs, rites, and beliefs of the Brahmins, and the adoption of the Brahminic way of life by a low caste seems to have been frequent, though theoretically forbidden. This process has been called -'Sanskritization'.
The development of Hinduism can be interpreted as a constant interaction between the religion of the upper social groups, represented by the Brahmans, and the religion of other groups. From the time of the Vedas (c. 1500 BCE) the indigenous inhabitants of the subcontinent tended to adapt their religious and social life to Brahmanic norms. This development resulted from the desire of lower- class groups to rise on the social ladder by adopting the ways and beliefs of the higher castes. The process, sometimes called "Sanskritization," began in Vedic times, when non-Vedic chieftains accepted the ministrations of Brahmans and thus achieved social status for themselves and their subjects. It was probably the principal method by which Hinduism spread through the subcontinent and into Southeast Asia. Sanskritization still continues in the form of the conversion of tribal groups, and it is reflected by the persistent tendency of low-caste Hindus to try to raise their status by adopting high-caste customs, such as wearing the sacred cord and becoming vegetarians, even though the castes have been officially abolished.
If Sanskritization has been the main means of spreading Hinduism throughout the subcontinent, the converse process, which has no convenient label, has been one of the means whereby Hinduism has changed and developed over the centuries. The Vedic people lived side by side with the indigenous inhabitants of the subcontinent. The phallic emblem of the god Shiva arose from a combination of the phallic aspects of the Vedic god Indra and a non-Vedic icon of early popular fertility cults. Many features of Hindu mythology and several of the lesser gods-such as Ganesha, an elephant-headed god, and Hanuman, the monkey god-were incorporated into Hinduism and assimilated into the appropriate Vedic gods by this means. Similarly, the worship of many goddesses who are now regarded as the consorts of the great male Hindu gods, as well as the worship of individual unmarried goddesses, may have originally incorporated the worship of non-Vedic local goddesses. Unorthodox circles on the fringes of Brahmanic culture (probably in southern India) were one of the important sources of the system of ecstatic devotional religion known as bhakti. Thus, the history of Hinduism can be interpreted as the imposition of orthoprax custom upon wider and wider ranges of people and, complementarily, as the survival of features of non-Vedic religions that gained strength steadily until they were adapted by the Brahmans.