Some of the initial work with EEXIST was based on trying to evolve a system that would respond to an influx of chemicals in one part of the system by infusing chemicals into nearby regions. This system actually evolved fairly quickly, and inspired the effort to further develop the system.
The next attempted evolution was a system for performing simple Boolean operations. Unfortunately, this never worked very well: the system just didn't seem naturally suite to binary behaviors.
At this point, a change in strategy developed, with the idea of observing what the system does, instead of trying to force it into particular behaviors (“seeking the artist vs. the engineer”). Beginning with random initial seedings of the system, the goal was to see if the system would develop cyclic or repeating behaviors. Basically, this was an attempt to evolve order from chaos.
This produced some interesting results, but a friend (Saulius) suggested the opposite approach: begin with a minimally-stimulated system, and see if it develops into repeating patterns. This worked very well: from initial configurations with just a few small regions of initial chemicals, complex/acyclic behaviors were sometimes observed. The nature of this transition from order to chaos is still being investigated.
Visual observation of the distribution of chemicals within the system is sometimes reminiscent of looking at frequency-domain plots. Code was added to the simulator to treat the chemical balance as a frequency spectrum, perform an inverse FFT into the time domain, and construct a WAV file corresponding to the sound pattern. You can find some of these WAV files here.