Evidence for both, acceleration and deceleration of evolution through learning can be found in the literature. We suggest a selection gradient model that allows to predict whether acceleration or deceleration is predominant. The main idea is that learning alters the genotype-to-fitness landscape, which determines selection pressure. Assuming that fittness can be split up into an innate and a learned component, conditions for the occurrence of the Baldwin and the Hiding effect are derived. We introduce learning curves to analyse what we term lifetime fitness. The infuence of the shape of the learning curve on the interaction between evolution and learning is analysed.