abstract = "In an attempt to address the scaling up of genetic
programming to handle complex problems, we have
proposed a hierarchical approach in which programs are
formed from independently evolved code fragments, each
of which is responsible for handling a subset of the
test input cases. Although this approach offers
substantial performance advantages in comparison to
more conventional systems, the programs it evolves
exhibit some undesirable properties for certain problem
domains. We therefore propose the introduction of a
self adaptive mechanism that allows the system
dynamically to focus evolutionary effort on the program
components most in need. Experimentation reveals that
not only does this technique lead to better-behaved
programs, it also gives rise to further significant
performance improvements.",