An example of design optimization for high evolvability: string rewriting grammar

As an example of the optimization of an evolutionary system design, a string rewriting system is studied. A set of rewriting rules that defines the growth of a string is experimentarily optimized in terms of maximizing the ʹreplicative capacityʹ, that is the occurrence ratio of self-replicating strings. It is shown that the most optimized rule set allows many strings to self-replicate by using a special character able to copy an original string sequentially. Then, using various different rewriting rule sets, the connectivity between self-replicating strings is studied. A set of ʹhyperblobsʹ covering the self-replicating strings is extracted and their connectivity is studied. The experimental results show that a large replicative capacity assures strong connectivity between self-replicating genotypes, making the system highly evolvable.