where the upper asymptote, c , is the distance from the initial trait mean measured in standard deviations of the initial phenotype distribution (at initialisation, VT = 1). We set this to two across all simulations. The rate at which the environmental suitability moves each generation is defined by a ’flattening constant’,m . An individual’s realised phenotypic value (zi ) is referenced against this optimum value,vt, at each timestep to calculate the individual’s fitness as a function of time.