It's the same with Scottish clans and allied clans. The oldest clans date back over a thousand years and sprouted off-shoots that would be 20 or 30 generations

It's the same with Scottish clans and allied clans. The oldest clans date back over a thousand years and sprouted off-shoots that would be 20 or 30 generations removed when counted back solely from the paternal (named) line (though sometimes the name passes through the maternal line, but this remove still holds). And while less endogamous than Indian castes, historically marriages between antagonist clans would likely be less frequent than between allied clans. Sometimes clans have expanded themselves by basically recruiting distant relatives who have a different surname. Offering them food or money to change their surname to the clan name.