It is this crucial distinction which allows us to define systems. The system exists as long its organisation remains. These two domains are distinct and don't interact, e.g. you cannot deduce a book from its pages. When two systems interact they trigger structural changes which may or may not trigger organisational changes. The system and its medium change together congruently.
Structural coupling is the manner of encountering between two systems.
Ontogenic drift arises in this process from adaptation, but no particular changes in a living system occur because of necessity. Behaviour is not something the system does. It is something that happens in the relationship between the living system and its medium. Both the system and the medium are constantly changing. It is not primarily a genetic phenomenon.