on the subject of clans….the clann system was largely built around the three-generation family unit. It was a system of mutual dependency, which grew through marriage, alliances, and the adoption and/or absorption of other peoples into the larger clan structure (which is why people of different names show up in clan territories).
The origins of the clan system are lost in the mists of time, but I think it’s fairly easy to see how such a system arose. A family unit settles in one particular place, which then becomes its “territory”. The elder branch of the family becomes the line of the lairds or clan chiefs (whose relatives would often be the “tacksmen” who apportioned living space and agricultural lands and received the rents). Over time, the “family” grows, until it isn’t really a family anymore, but rather a tribe occupying a certain area and all owing allegiance to the chief.