2 Controlling Diversity

Is there an ideal level of a particular type of diversity? The two recognised phases of the evolutionary process, exploration followed by exploitation [Eiben and Schippers, 1998], make this question difficult to answer. Without knowing a priori the existence of a type and ideal levels of diversity, blindly controlling diversity in a population seems problematic. Instead, two different diversity strategies may be required: a diversification and an intensification strategy, similar to those explicitly defined in tabu search [Glover and Laguna, 1997]. A related method was recently defined in genetic programming based on edit distance and adaptive control based on fitness improvement [Ekárt and Németh, 2000]. However, the exploration and exploitation aspects of search are not the only issues to consider when attempting to control or modify population diversity. A fuller discussion of methods used to control diversity is presented in Chapter 4.