The nature and source of evolutionary trends in complexity is difficult to
assess from the fossil record, and the driven vs. passive nature of such trends
has been debated for decades. There are also questions about how effectively
artificial life software can evolve increasing levels of complexity. We extend
our previous work demonstrating an evolutionary increase in an information
theoretic measure of neural complexity in an artificial life system
(Polyworld), and introduce a new technique for distinguishing driven from
passive trends in complexity.