Analysing the Regularity of Genomes Using Compression and Expression Simplification

We propose expression simplification and tree compression as aids in understanding the evolution of regular structure in Genetic Programming individuals. We apply the analysis to two previously-published algorithms, which aimed to promote regular and repeated structure. One relies on subtree duplication operators, the other uses repeated evaluation during a developmental process. Both successfully generated solutions to difficult problems, their success being ascribed to promotion of regular structure. Our analysis modifies this ascription: the evolution of regular structure is more complex than anticipated, and the success of the techniques may have arisen from a combination of promotion of regularity, and other, so far unidentified, effects.