No it’s not a purely blank slate. But it is not purely a biological or “natural” thing, either, that simply does what it needs to do out of necessity. If that were true, cultures would never die from sociological causes, but they do. See my reply to jsroberts for more. And let’s try to avoid lumping people into groups. That’s not arguing, that’s a kind of name calling.
Each branch is limited to the reality of its time of existence, the question is what do we do when situations change - when the ability to change can occur, but would of course have SOME cost or consequence, but the benefit would be arguably greater. Then change becomes purely a matter of decision and will, not natural constraints.
EDIT: also, just because something was decided to be a certain way doesn’t mean it was the best or most beneficial (for the culture) decision even at the time.
