Complex organisms, such as multi-cellular ones, have neither emerged spontaneously, nor evolved directly, from a disorganised mass of quarks. Stable intermediary sub-systems, like atoms and uni-cellular organisms, had to occur first and serve as reusable blocks for more complex systems to build upon. The occurrence of structured systems, featuring internal diversity, from uniform self-adaptive sub-systems is a key phenomenon to study in this context. We believe this phenomenon relies on the interactions among self-adaptive sub-systems, both at the micro-level (directly between sub-systems) but most importantly via macro-levels (indirectly via aggregate information and control from/to all sub-systems). To study this, we have developed a hierarchical control simulator based on self-adaptive cellular automata (CA). This paper presents our Holonic Cellular Automata (HCA) simulator, and the preliminary results showing the occurrence of structure / diversity from micro-macro feedback loops among self-adaptive CAs starting in the same states. This provides a promising basis for further investigations into the range of possibilities concerning structure creation, as a key enabler for the emergence of complex systems.