Adaptive Landscapes

Fisher’s geometrical model and Wright’s rugged landscape are described. Pleiotropy is not universal as Fisher had supposed. Long-term evolution experiments were unable to resolve landscape topologies. Evaluating the fitnesses in combinatorially complete sets of mutations shows landscapes are moderately rough. Criticism is leveled at other poorly executed experiments. The linear additive model is described and the impact of the scale of measurement on epistasis is discussed. Landscapes are classified according to the nature of the epistasis present. The likely route an adaptive walk takes through a landscape is described. Because no mechanisms connect the genotypes to their fitnesses in these landscapes, so no global predictions can be made. For example, one cannot be certain that an experimentally identified adaptive peak would remain a peak in the presence of additional mutations. Finally, attributing causality to descriptive terms like pleiotropy and epistasis is shown to be a fool’s errand.