Just because it's based on something else, it doesn't mean it can't be much more complex.
All Shakespeare writings are based on 26 English letters and a few punctuation signs.
Evolved systems are rarely obvious. On the surface they are simple, but once you dig deep, there are systems that are interconnected, systems that depend on side effects of other systems and their own side effects.
Go look up metabolic pathways diagrams. These are the diagrams for some relatively simple processes:
