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Effect of Crossover on Fitness

As expected in the initial generations crossover is highly disruptive (cf. Figure 9) with only 19.5% of crossovers producing a child with the same score as its first parent (i.e. the parent from which it inherits the root of its tree). However after generation 4 this proportion grows steady, by generation 18 more than half have the same fitness. At the end of the run this has risen to 69.8%.

The range of change of fitness is highly asymmetric; many more children are produced which are worse than their parent than those that are better. By the end of the run, no children are produced with a fitness greater than their parent. Similar behaviour has been reported on other problems [12] [21, page 183,] [15, Chapter 7,].

Figure 9:   Fitness relative to First Parent, Normal runs, Means of 50 runs.

William B Langdon
Tue Jun 10 12:12:55 BST 1997