profession. Many theories have been propounded to explain this system. According to the Vedic theories, the Brahmins are direct descendants of seven sages who are believed to be the sons of Brahma, born out of his mind through yogic prowess. They are (1) Atri, (2) Bharadvaja, (3) Gautama Maharishi, (4) Jamadagni, (5) Kashyapa, (6) Vasishta and (7) Vishvamitra. To this list, Agastya is also sometimes added. These eight sages are called gotrakarins, from whom all 108 gotras (especially of the Brahmins) have evolved. For instance, from Atri sprang the Atreya and Gavisthiras gotras. According to Robert Vane Russell, many gotras of Hindu religion are of totemic origin which is named after plants, animals, and natural objects. These are universal among tribes but occur also in Hindu castes. The commonest totem names are those of animals, including several which are held sacred by Hindus, as bagh or Nahar, the tiger; bachhas, the calf; murkuria, the peacock; kachhua, the tortoise; nagas, the cobra; hathi, the elephant; bhains, the buffalo; richaria, the bear; Kuliha, the Jackal, Kukura, the dog; kursaal, the deer; Hiran, the black-buck and so on. The utmost variety of names is found, and numerous trees, as well as rice and other crops, salt, sandalwood, cucumber, pepper, and some household implements such as pestle, rolling slab, serve as the names of clans. Thus the name of the rishi Bharadvaja means a lark bird, and Kaushika means descended from Kusha grass, Agastya from Agassi flower, Kashyapa from kachhap a tortoise, Taittiri from titer, partridge bird. Similarly, the origin of other rishis is attributed to animals, Rishyasringa to an antelope, Mandavya to a frog, Kanada to an owl. The usual characteristic of totemism is that the members of a clan regard themselves as related to or descended from, the animals or trees from which the clan takes its name, and abstain from killing or eating them. A gotra must be distinguished from a kula. A kula is equal to a particular family, or equal to modern-day "clans". A kula relates to a lineage or a caste. Marriages and gotras Marriages within the gotra ('sagotra' marriages) are not permitted under the rule of exogamy in the traditional matrimonial system. The compound word 'sagotra' is a union of the words 'sa' and 'gotra', where 'sa' means same or similar. It is common practice in preparation for Hindu marriage to inquire about the kula-gotra (clan lineage)