Special Forms of Evolution

Abstract

13.1 Aims of this Chapter In this chapter we discuss special forms of evolution that in some sense de-viate from the standard evolutionary algorithms. In particular, we present coevolution and interactive evolution that both work under "external influ-ence". In coevolution the influence comes from another population, whose members affect the fitness of the main population. In turn, the main popu-lation also influences the fitness of the other one; hence the two populations evolve together. In interactive evolution this influence comes from a user who defines the fitness values by subjective preferences. In both of these cases, the fitness that is awarded to a solution may vary. In the first case because the fitness is dependent on the evolutionary state of the second population, and in the second because users often display inconsistencies. We finish this chapter by describing evolutionary approaches to problems where changing evalua-tion criteria form the very feature defining them: nonstationary optimisation problems. 13.2 Coevolution Previously in this book we made extensive use of Sewall-Wright 's analogy of the adaptive landscape where an evolving population is conceptualised as moving on a surface whose points represent the set of possible solutions. This metaphor ascribes a vertical dimension to the search space that denotes the fitness of a particular solution, and the combined effects of selection and vari-ation operators move the set of points into high-fitness regions. l Whilst this is an attractive metaphor, it can also be profoundly misleading when we consider the adaptation of a biological species. This is because it tends to lead to the implicit notion that solutions have a fitness value per 1 Although it can be shown that the reverse can sometimes happen [321].