[Lurking Libertarian]

I would say "tribes" are pretty natural. What "positive law" creates them?

Tribes have rules about who's in and who's out. They make those rules; they don't find them written in the clouds.

[DiogenesLamp]

Tribes have rules about who's in and who's out. They make those rules; they don't find them written in the clouds.

You're kidding, right? Their rules are "if you are born of our people, then you are a member of our tribe."

"If you are a woman taken from another tribe, now you are a member of ours."

Pretty much the United States, circa 1787.

It doesn't get simpler than that.