abstract = "We have investigated structural distance metrics for
linear genetic programs. Causal connections between
changes of the genotype and changes of the phenotype
form a necessary condition for analyzing structural
differences between genetic programs and for the two
objectives of this paper: (i) The distance information
between individuals is used to control structural
diversity of population individuals actively by a
two-level tournament selection. (ii) Variation distance
of effective code is controlled for different genetic
operators - including a mutation operator that works
closely with the applied distance measure. Numerous
experiments have been performed for three benchmark
problems.",