Gothra

Gothra especially among Hindus is a subject matter of research on social and spiritual front as well as scholarly treatment by Indian and foreign scholars over the ages.. One theory which seems most plausible regarding gothras is that people of a geographic area, or votaries to certain ways of thinking just assembled under some leader.. or a person of the group with leadership qualities ..and such groups started to be called gothras under the name of the leader,, Maybe the common guru also could have been named as the presiding entity ..

So there are gothras in Hinduism among all the three varnas..

The reason why there was no intermarriage among the persons of the same gothras, might be among other things that the persons gathered together in one gothram felt a sort of feeling of being siblings, and this feeling would have galled the conscience of the groups..as marriages or reproductive contacts in such cases would amount to incest. Even if this may not be the only reason, it must have been a compelling reason..The Indian social structure was predominantly male-oriented and the females brought in assumed the identity of their male marital partner..

It is not clear whether the gothras came into existence before the castes like brahmins, Kshatriya etc were demarcated or earlier..

Genetic similarities can occur in respect of even cousins of the paternal or maternal hierarchy.. And any race must have started with some sort of limited population, and even in Vedas and old lore, some incestual procreation are indicated.. ( I do not use the word incest here as an abhorrent social custom, but nature definitely wants to preserve any species, and if only a brother and sister, or father and daughter are the sole living elements, in all probability they would have mated..) So genetic similarites must be on racial basis rather than gothra considerations in the beginning.. But the strict rules prohibiting Varnasankara (we can see this in smrithis and even in gita), would have created exclusiveness later on the basis or Varna and Gothra..

However, this is an issue where anyone can put forth any theory.. and any theory will be plausible in a certain way..