The kind of part makes no difference, it could be an atom, molecule, neuron, morpheme, or even a computer bit. Complexity Theory deals with the potential evolutionary behavior of macroscopic collections of these parts. Their interactions lead to emergent properties, coherent collective phenomena that can only be described at levels higher than those of the individual units. For Complexity to emerge in a system two components are necessary. The first is Time , an irreversible medium where things can happen.
Time flows from a closed and ordered past to an open and chaotic future.
In such a system we can regard the border between the past and future, i.e. Now , as the Edge of Chaos, that point in a system where Complex Adaptive behavior can most easily occur. It should be noted that at the quantum level time can flow in either direction. The second element is nonlinearity . Nonlinear systems do not obey the simple rules of addition. Small effects on one level of organization produce large effects at the same or different levels.