Neutral networks in an evolutionary robotics search space

Recent work has argued for the importance of non-adaptive neutral evolution in optimisation over difficult search landscapes. In this paper we show that the search process underlying a difficult evolutionary robotics problem does indeed show phases of neutral evolution. The noise in evaluated fitness of a single genotype is shown to be able to account for the variance in fitness across a long period of the evolutionary run. We further show that the population moves significantly in genotype space during this neutral phase, possibly increasing in divergence. Finally, we investigate the probabilities of mutating to a higher fitness, above the neutral plateau, and find no evidence for a significant upward trend in these probabilities before the crucial mutations actually occurred.