This paper examines measures of diversity in genetic programming. The goal is to understand the importance of such measures and their relationship with fitness. Diversity methods and measures from the literature are surveyed and a selected set of measures are applied to common standard problem instances in an experimental study. Results show the varying definitions and behaviours of diversity and the varying correlation between diversity and fitness during different stages of the evolutionary

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... ocess. Populations in the genetic programming algorithm are shown to become structurally similar while maintaining a high amount of behavioural differences. Conclusions describe what measures are likely to be important for understanding and improving the search process and why diversity might have different meaning for different problem domains.