There also is only an arbitrary artificial border between a branch and a leaf or the tree and the ground it grows from. You're right that in ultimo, all these

There also is only an arbitrary artificial border between a branch and a leaf or the tree and the ground it grows from. You're right that in ultimo, all these distinctions are artificial and determined by humans - but they have use in our interactions and survival. Culture is significant in those interactions, if you met a random person somewhere in the wilderness and your survival is dependent on not offending this single person, culture suddenly becomes a very real thing to you (despite that person probably being pretty friendly and hospitable in reality). For most of us, in highly specialized and commoditized societies with lots of intercultural communication, these boundaries have blurred somewhat but it doesn't mean the concept is entirely inapplicable.