The contents of the massive banks behind these successive revetments makes it quite clear that the material was derived from the incorporation of earlier occupation levels.
But in fact, when you try to model that on a computer you find that because of the very structure of matter and of the chemical bonds that are the basis of every organism, evolution is not random at all. It will tend to follow certain paths.
No written law has ever been more binding than unwritten custom supported by popular opinion.