The Role of Mate Choice in Biocomputation: Sexual Selection as a Process of Search, Optimization and Diversification

The most successful, complex, and numerous species on earth are composed of sexually-reproducing animals and flowering plants. Both groups typically undergo a form of sexual selection through mate choice: animals are selected by conspecifics and flowering plants are selected by heterospecific pollinators. This suggests that the evolution of phenotypic complexity and diversity may be driven not simply by natural-selective adaptation to econiches, but by subtle interactions between natural selection and sexual selection. This paper reviews several theoretical arguments and simulation results in support of this view. Biological interest in sexual selection has exploded in the last 15 years (see Andersson, 1994; Cronin, 1991), but has not yet been integrated with the biocomputational perspective on evolution as a process of search and optimization (Holland, 1975; Goldberg, 1989). In the terminology of sexual selection theory, mate preferences for ‘viability indicators’ (e.g. Hamilton & Zuk, 1982) may enhance evolutionary optimization, and mate preferences for ‘aesthetic displays’ (e.g. Fisher, 1930) may enhance evolutionary search and diversification. Specifically, as a short-term optimization process, sexual selection can: (1) speed evolution by increasing the accuracy of the mapping from phenotype to fitness and thereby decreasing the ‘noise’ or ‘sampling error’ characteristic of many forms of natural selection, and (2) speed evolution by increasing the effective reproductive variance in a population even when survival-relevant differences are minimal, thereby imposing an automatic, emergent form of ‘fitness scaling’, as used in genetic algorithm optimization methods (see Goldberg, 1989). As a longer-term search process, sexual selection can: (3) help populations escape from local ecological optima, essentially by replacing genetic drift in Wright's (1932) “shifting balance” model with a much more powerful and directional stochastic process, and (4) facilitate the emergence of complex innovations, some of which may eventually show some ecological utility. Finally, as a process of diversification, sexual selection can (5) promote spontaneous sympatric speciation through assortative mating, increasing biodiversity and thereby increasing the number of reproductively isolated lineages performing parallel evolutionary searches (Todd & Miller, 1991) through an adaptive landscape. The net result of these last three effects is that sexual selection may be to macroevolution what genetic mutation is to microevolution: the prime source of potentially adaptive heritable variation, at both the individual and species levels. Thus, if evolution is understood as a biocomputational process of search, optimization, and diversification, sexual selection can play an important role complementary to that of natural selection. In that role, sexual selection may help explain precisely those phenomena that natural selection finds troubling, such as the success of sexually-reproducing lineages, the speed and robustness of evolutionary adaptation, and the origin of otherwise puzzling evolutionary innovations, such as the human brain (Miller, 1993). Implications of this view will be discussed for biology, psychology, and evolutionary approaches to artificial intelligence and robotics.